Skip to main content
NCBI home page
ACS Omega logoLink to ACS Omega
. 2021 Nov 16;6(47):31578–31594. doi: 10.1021/acsomega.1c04061

Geochemistry and Organic Petrology of Middle Permian Source Rocks in Taibei Sag, Turpan-Hami Basin, China: Implication for Organic Matter Enrichment

Huan Miao †,*, Yanbin Wang †, Shihu Zhao †, Jianying Guo ‡,*, Xiaoming Ni §, Xun Gong †, Yujian Zhang †, Jianhong Li †
PMCID: PMC8637588  PMID: 34869983

Abstract

graphic file with name ao1c04061_0022.jpg

The Taodonggou group of Middle Permian is an important source rock in Taibei sag of Turpan-Hami basin. Due to its deep burial, drilling has only been revealed in recent years. Based on organic petrology and organic geochemistry experiments, this paper studies the organic petrology, organic geochemistry, sedimentary environment, and hydrocarbon generation potential of source rocks in Taibei sag, Turpan-Hami basin, and reveals the influence of the sedimentary environment on the organic matter abundance of source rocks. The results are as follows: (1) The organic matter of the Middle Permian source rocks in Taibei sag of Turpan-Hami basin is mainly sapropelite and exinite. The vitrinite is mainly vitrodetrinite, and the exinite is mainly lamalginiite. (2) The total organic carbon content value is 0.55–6.08 wt %, and the average value is 2.58 wt %. The PG value ranges from 0.78 mg HC/g to 30.86 mg HC/g, and the average value is 4.88 mg HC/g. Chloroform asphalt “A” is 0.046–0.8767 wt %, and the average value is 0.285 wt %. The types of organic matter are mainly III and II–III, and the Ro value is 0.628–1.49 wt % (average = 0.988 wt %). The Tmax distribution is 329–465 °C. The average temperature is 434.7 °C, which is in the mature stage (oil window stage). The Middle Permian source rocks are mainly very good to excellent source rocks with a good hydrocarbon generation potential. (3) The source rocks are deposited in a semihumid and semiarid climate. Organic matter is input as a mixed source. The early and late stages is dominated by terrestrial higher plants. The middle stage is dominated by lower aquatic organisms, and the sedimentary environment consists of weak reduction and weak oxidation environments. (4) In the study area, the abundance of organic matter has a weak negative correlation with CPI and a positive correlation with Pr/Ph and ∑C21–/∑C22+. Under the coaction of paleoclimate, organic matter input, and redox environment, the enrichment model of organic matter with high productivity and weak oxidation environment characteristics can also form excellent source rocks. This study is of great significance and provides theoretical guidance for the exploration of deep oil and gas resources.

1. Introduction

Source rock is the material basis of the petroliferous basin. The quality of a source rock is often determined by the exploration and development of petroliferous basin. With the progress of exploration technology and the growing demand for energy,1 it is difficult to meet the actual needs of social development with shallow oil and gas resources, so it is necessary to shift the focus of oil and gas exploration to deep, ultra deep, and unconventional oil and gas fields.2−6

The Middle Permian in Turpan-Hami basin has always been one of the important exploration strata in the Turpan-Hami oilfield. The discovered Lukeqin, Shanshan, and other oil- and gas-bearing structures show the good exploration potential of this set of strata.7 The Middle Permian strata are widely distributed in Taibei sag, which has been rated as the key area for pre-Jurassic exploration in the Turpan-Hami oilfield by many resource evaluations.

Although the mudstone of the Middle Permian Taodonggou group in Taibei sag has been proved to be an effective source rock,8 due to its deep burial, less drilling exposure, and poor quality of seismic data,9 the exploration degree is low. In addition, the previous understanding of the organic geochemical characteristics and hydrocarbon generation potential of this set of strata came from outcrops, which led to the lack of understanding of its geochemical characteristics.

Based on the latest drilling core and cuttings samples, this paper systematically revealed the organic petrology, geochemical characteristics, sedimentary environment, and hydrocarbon generation potential of Middle Permian Taodonggou source rocks in Taibei sag, Turpan-Hami basin, using organic petrology and organic geochemistry experiments, and analyzed the influence of the sedimentary environment on the enrichment of organic matter in source rocks.

2. Geological Setting

Turpan-Hami basin is one of the important petroliferous basins in Northwest China (Figure 1a). It is a sedimentary basin developed on the folded basement of the Early Paleozoic. It has experienced the filling stage of fault depression in Permian Triassic and the evolution stage of the foreland basin since Jurassic.10−12 From east to west, it can be divided into Hami depression, liaodun uplift, and Turpan depression7 (Figure 1b).

Figure 1.

Figure 1

Open in a new tab

Geological overview of the Turpan-Hami Basin and of the study area: (a) location of the Turpan-Hami Basin; (b) tectonic units of the Turpan-Hami Basin and location of the study area;7 and (c) stratigraphic column of the Permian Taodonggou group in YT1.

Taibei sag is a secondary sag of Turpan Sag (Figure 1b), with an area of 9600 m2. The latest seismic and drilling data show that there are carboniferous quaternary strata in the study area, with a maximum thickness of 9000 m. Among them, the Middle Permian Taodonggou group argillaceous source rocks are stably distributed in the study area (Figure 1c), with an average thickness of about 100 m and a burial depth ranging from 4000 to 6500 m.

3. Samples and Experiments

Thirty-two mudstone samples of Taodonggou group were collected from the TELG profile, YT1 well, and L30 well, including 28 drilling samples (17 samples from the YT1 well and 11 samples from the L30 well) and 4 samples from the TELG profile. The whole-rock microcomponent, kerogen, vitrinite reflectance, rock-eval, Soxhlet extraction, and gas chromatography-mass spectrometry (GC-MC) were carried out.

According to the Chinese National Standard GB/T 16773-2008, the whole-rock macerals were measured and quantified by polarizing the microscopic system and hot stage (model: Axioskop 40, No.: 0700380Y). Based on the Chinese Industry Standard SYT 5124-2012, the vitrinite reflectance of Taodonggou group mudstone was obtained by an MSP UV–vis 2000 spectrometer. Based on the Chinese National Standard GB/T 18602-2012, the geochemical parameters of mudstone samples were obtained by a YQ-VII pyrometer. According to the Chinese National Standard GB/T 19145-2003, the total organic carbon content (TOC) of mudstone samples was determined by an ACS744 carbon sulfur analyzer. Chloroform asphalt “A” is determined by Soxhlet extraction. According to the China Petroleum Industry Standard SYT 5118-2005, mudstone samples are crushed to less than 120 mesh and extracted for 72 h. The gas chromatography-mass spectrometry (GC-MC) experiment is completed by the Key Laboratory of Natural Gas Accumulation and Development of CNPC. The system consists of a high-temperature pyrolyzer produced by SGE company in Australia, a HP 5890A gas chromatograph produced by HP Company in the United States, and a microcomputer data system.

4. Results

4.1. Organic Petrology

The vitrinite of source rocks in Taibei sag is turned from gray-white to gray-black under the reflected light of oil immersion, mainly composed of vitrodetrinite, and some of them contain telocollinite and telinite 2. The exinite is beige and orange-yellow in blue fluorescence, and it is mainly lamalginiite. The inertinite is grayish-white and mainly composed of inerodetrinites (Figure 2).

Figure 2.

Figure 2

Open in a new tab

Maceral photos of source rocks of the Middle Permian Taodonggou group in Taibei sag: (a) Vitrodetrinite; (b) telinite 2; (c) telinite 2; (d) vitrodetrinite; (e) vitrodetrinite; (f) inerodetrinites; (g) exinite; (h) exinite; and (i) lamalginiite.

Table 1 shows the contents of whole-rock macerals and kerogen components of Taodonggou group source rocks.

Table 1. Whole-Rock Macerals and Kerogen Macerals of Taodonggou Group Source Rocks in Taibei Sag.

    whole-rock macerals
 macerals of kerogen
well and profile depth (m) vitrinite (%) inertinite (%) exinite (%) vitrinite (%) inertinite (%) exinite + sapropelic (%)
L-30 5062.35       2 10 88
L-30 5013 74 2 24      
L-30 5030 62 15 23 11 46 43
L-30 5038 88 7 5      
L-30 5041 80 12 8      
L-30 5060 72 18 20 6 52 42
L-30 5064 60 25 15 7 41 52
L-30 5070 85 5 10 14 41 45
L-30 5076 90 4 6      
YT-1 6092 40 37 23      
YT-1 6140       8 23 69
YT-1 6142–6144 85 5 10 6 26 68
YT-1 6147 80 10 10 5 30 65
YT-1 6151 78 7 15 85 5 10
YT-1 6154       80 10 10
YT-1 6160–6162       78 7 15
YT-1 6144.7       15 23 62
YT-1 6145.3       58 4 38
YT-1 6145.8       12 53 35
TELG         42 20 38
TELG         33 28 39
TELG         40 18 42
TELG         30 12 58
Open in a new tab

The results of whole-rock maceral quantitative experiments show that the organic matter of Taodonggou group source rocks is mainly vitrinite, and the vitrinite content can reach 40–90%, with an average of 74.5%. The content of exinite ranges from 5 to 24%, with an average of 13.25%. The content of inertinite ranges from 2 to 37% (average = 12.25%). The content of vitrinite in the L-30 well is 60–90%, with an average of 76.4%. The content of exinite ranges from 5 to 24%, with an average of 12.6%. The content of inertinite ranges from 2 to 25% (average = 11%). The content of exinite in the YT-1 well ranges from 40 to 85%, with an average of 70.75%. The content of exinite ranges from 10 to 23%, with an average of 14.5%. The content of inertinite ranges from 5 to 37% (average = 11%) (Figure 3a,c).

Figure 3.

Figure 3

Open in a new tab

Whole-rock macerals and kerogen macerals: (a) trigonometry of whole-rock macerals; (b) trigonometry of kerogen macerals; (c) histogram of the whole-rock maceral content; and (d) histogram of the kerogen maceral content.

A whole-rock analysis can only analyze morphological organic matter but cannot study and quantitatively analyze “amorphous” components,13 so the whole-rock analysis cannot accurately quantify organic macerals of source rocks. If we want to find out the organic petrological characteristics of the source rocks of the Middle Permian Taodonggou group, we must purify the organic matter in the source rocks.

After purification of organic matter from mudstone samples, it is found (Figure 3b,d) that the main macerals of source rocks in Taodonggou group are exinite and sapropelite, with the content of 35–88% and an average value of 57.28%, followed by inertinite formations, with the content of 4–53% and an average value of 27.17%. The content of vitrinite ranges from 1 to 58%, with an average of 15.55%. In the L-30 well, the contents of exinite and sapropelite range from 42 to 88%, with an average value of 54%; the contents of inertinite range from 10 to 52%, with an average value of 38%; and the contents of vitrinite range from 2 to 14% (average = 8%). In the YT-1 well, the contents of exinite and sapropelite range from 35 to 88%, with an average value of 64.89%; the contents of inertinite range from 4 to 53% (average = 22.23%); and the contents of vitrinite range from 1 to 53%, with an average value of 12.79%. The contents of exinite and sapropelite in the TELG profile range from 38 to 58%, with an average value of 44.25%, the contents of inertinite range from 12 to 28% (average = 19.5%), and the contents of vitrinite range from 30 to 42%, with an average value of 36.25%.

Therefore, the organic matter of the Middle Permian source rocks in Taibei sag of Turpan-Hami basin is mainly sapropelite and exinite, the vitrinite is mainly vitrodetrinite, and the exinite is mainly lamalginiite.

4.2. Organic Geochemistry

Table 2 shows the geochemical characteristics of Taodonggou group source rocks, including total organic carbon (TOC), hydrocarbon generation potential (PG), chloroform asphalt A, maximum pyrolysis peak temperature (Tmax), hydrogen index (HI), and vitrinite reflectance (Ro).

Table 2. Geochemical Characteristics of Source Rocks of Taodonggou Group, Taipei Sag.

well and profile depth (m) TOC (%) S1 (mg HC/g) S2 (mg HC/g) PG (mg HC/g) chloroform asphalt A (%) Tmax (°C) Ro (%)
L-30 5062.35 4.32 0.2008 4.1837 4.3918 0.0949 447 1.18
L-30 5012–5014 2.01 7.1678 7.1432 14.3842 0.3351 329 1.124
L-30 5019 0.8 0.6679 1.519 2.2098 0.1899 343 1.141
L-30 5030 4.17 0.307 3.1118 3.436 0.3442 445 0.99
L-30 5038 3.44 0.2838 1.9624 2.3143   446 0.978
L-30 5048–5054 3.63 0.3631 2.1673 2.5474   444 0.926
L-30 5060 4.39 0.2563 2.2899 2.564 0.1875 443 0.824
L-30 5064 4.51 0.3595 3.5677 3.9384 0.2103 445 1.173
L-30 5070 3.45 0.3584 2.6268 2.9963   443 1.025
L-30 5074–5078 3.53 0.2253 2.6557 2.8871 0.059 444 1.134
L-30 5080 3.33 0.2191 2.4389 2.664 0.1282 444 1.004
YT-1 6077 0.66 0.2547 0.5702 0.8429 0.0791 432 0.937
YT-1 6084 0.55 0.2399 1.0558 1.3   432 0.922
YT-1 6092 0.73 0.2512 1.0861 1.3411   429 1.137
YT-1 6102 0.86 0.2351 1.1887 1.4285   403 1.201
YT-1 6110–6116 0.66 0.2224 1.1053 1.3312 0.0791 448 1.29
YT-1 6122 0.71 0.3232 1.6788 2.0088   422 0.94
YT-1 6126–6132 1.07 0.4221 2.2339 2.6581 0.1377 444 1
YT-1 6136 0.95 0.4221 2.3554 2.7796   440 1.15
YT-1 6140 5.37 0.7973 3.9698 4.7785   465 1.32
YT-1 6142–6144 4.03 0.7681 3.5093 4.2846 0.3428 452 1.34
YT-1 6147 4.2 1.2098 5.0547 6.2746   450 1.201
YT-1 6151 0.92 0.3466 2.12 2.4722 0.1608 438 0.94
YT-1 6154 0.83 0.2831 1.6397 1.929 0.1303 393 1.07
YT-1 6160–6162 0.58 0.3739 1.6608 2.0364 0.1042 389 1.05
YT-1 6144.7 1.21 0.1342 0.643 0.7783 0.8767 468 1.26
YT-1 6145.3 3.18 1.6712 6.192 7.8632 0.7095 464 1.49
YT-1 6145.8 2.94 0.4151 2.0075 2.4351   464 1.04
TELG   0.66 0.1903 2.0005 2.1948 0.046 446 0.53
TELG   3.29 1.125 13.9591 15.0897 0.1463 445 0.65
TELG   2.43 0.4942 13.4866 13.9873 0.1904 448 0.55
TELG   5.13 0.7543 30.0974 30.8658 0.2439 455 0.62
Open in a new tab

Rock-evals and Soxhlet extraction experiments show that the TOC value of the Middle Permian Taodonggou group source rocks in Taibei sag ranges from 0.55 to 6.08%, with an average value of 2.58 wt %. The hydrocarbon generation potential (PG) ranges from 0.78 mg HC/g to 30.86 mg HC/g, with an average value of 4.88 mg HC/g. Chloroform asphalt A ranges from 0.046 to 0.8767% (average = 0.2358%). The TOC value of the L30 well ranges from 0.8 to 4.51 wt %, with an average value of 3.416 wt %; the distribution of hydrocarbon generation potential ranges from 2.201 to 14.382 mg HC/g, with an average value of 4.286 mg/g; and chloroform asphalt A ranges from 0.059 to 0.3442 wt % (average = 0.1936%) (Figure 4a–c). The TOC value of the YT1 well ranges from 0.53 to 6.081 wt %, with an average value of 1.902 wt %; the distribution of hydrocarbon generation potential ranges from 0.77 to 8.306 mg HC/g, with an average value of 2.76 mg HC/g; and chloroform asphalt A ranges from 0. 0791 to 0.8767 wt % (average = 0.3176 wt %) (Figure 4d–f). The TOC value of the TELG profile ranges from 0.66 to 5.13 wt %, with an average value of 2.88 wt %; the hydrocarbon generation potential distribution ranges from 2.19 to 30.86 mg HC/g, with an average value of 15.53 mg HC/g; and chloroform asphalt A ranges from 0.046 to 0.2439 wt % (average = 0.1567 wt %) (Figure 4g–i). According to the TOC value, the abundance of organic matter in the L30 well is higher than that in the TELG profile and YT1 well. According to the hydrocarbon generation potential (PG), organic matter abundance in the TELG profile is higher than that in L30 and YT1 wells. According to chloroform asphalt A, organic matter abundance in the YT1 well is higher than that in the TELG profile and L30 well. Compared with the organic matter abundance of TELG outcrop and drilling samples, the results show that weathering has little or no impact on TELG profile samples.

Figure 4.

Figure 4

Open in a new tab

Frequency distribution histogram of organic matter abundance in source rocks of Taodonggou group in Taibei sag: (a–c) the frequency distribution histogram of TOC, PG, and chloroform asphalt A in the L-30 well, respectively; (d–f) the frequency distribution histogram of TOC, PG, and chloroform asphalt A in the YT-1 well respectively; and (g–i) the frequency distribution histogram of TOC, PG, and chloroform asphalt A in the TELG profile, respectively.

The maximum pyrolysis temperature (Tmax) of source rocks in Taibei sag ranges from 329 to 468 °C (average = 434.375 °C); the maximum pyrolysis temperature (Tmax) of the L-30 well ranges from 329 to 447 °C, with an average value of 422.6 °C; the maximum pyrolysis temperature (Tmax) of the YT1 well ranges from 389 to 468 °C, with an average value of 437.235 °C; and the maximum pyrolysis temperature (Tmax) of the TELG profile ranges from 445 to 455 °C, with an average value of 448.5 °C (Figure 5a–c).

Figure 5.

Figure 5

Open in a new tab

Frequency distribution histogram of Tmax in source rocks of Taodonggou group in Taibei sag: (a) L-30 well, (b) YT-1 well, and (c) TELG profile.

The vitrinite reflectance (Ro) of source rocks in Taibei sag ranges from 0.53 to 1.49%, with an average value of 1.048%. Among them, the vitrinite reflectance (Ro) of the L-30 well ranges from 0.824 to 1.173%, with an average value of 1.04%. The vitrinite reflectance (Ro) of the YT1 well ranges from 0.94 to 1.49%, with an average value of 1.168%. The vitrinite reflectance (Ro) of the TELG profile ranges from 0.53 to 0.65%, with an average value of 0.588% (Figure 6a–c).

Figure 6.

Figure 6

Open in a new tab

Frequency distribution histogram of Ro in source rocks of Taodonggou group in Taibei sag: (a) L-30 well, (b) YT-1 well, and (c) TELG profile.

4.3. Biomarker Compounds

Table 3 shows the biomarker characteristics of 15 mudstone samples from Taodonggou group in the study area, including n-alkanes, isoprene alkanes, steranes, and terpanes.

Table 3. Biomarkers of Source Rocks in Taodonggou Group, Taibei Sag.

        n-alkanes
 isoprene like alkanes
 sterane
 terpane
well and profile depth (m) C no. range main peak C no. CPI 0EP ∑C21–/∑C22+ Pr/Ph Pr/nC17 Ph/nC18 C27 (%) C28 (%) C29 (%) C29 20S/(20R + 20S) C29 ββ/(αα + ββ) C19/C23 C20/C23 C24/C23 Ts/Tm C29/C30 GI
YT1 6110–6116 14–38 29 1.42 1.42 0.30 1.16 1.08 0.46 21.67 21.28 57.05 0.31 0.52 0.90 1.56 0.52 0.30 0.51 0.36
YT1 6126–6132 13–38 18 1.41 0.78 0.75 1.14 0.36 0.25 21.41 14.37 64.22 0.31 0.53 1.01 1.63 0.48 0.50 0.50 0.22
YT1 6142–6144 14–37 18 1.30 0.86 0.59 1.16 0.35 0.26 28.25 13.52 58.23 0.33 0.48 1.00 1.51 0.55 0.54 0.48 0.20
YT1 6144.70 15–37 18 1.14 0.98 1.01 0.81 0.17 0.17 41.20 22.31 36.49 0.49 0.48 0.15 0.44 0.60 0.47 0.63 0.22
YT1 6145.30 13–37 17 1.12 0.99 2.26 2.93 0.19 0.07 40.20 21.31 38.49 0.42 0.49 1.01 0.84 0.76 0.55 0.43 0.76
YT1 6145.80 13–37 17 1.05 0.99 1.88 1.70 0.17 0.10 44.43 18.15 37.42 0.35 0.53 0.45 0.59 0.69 0.58 0.77 0.32
YT1 6154.00 14–41 29 1.32 1.33 0.39 0.94 0.47 0.43 27.09 12.17 60.74 0.32 0.52 1.04 1.25 0.51 0.51 0.49 0.22
YT1 6160–6162 14–40 29 1.35 1.34 0.41 0.94 0.65 0.53 28.86 11.04 60.10 0.34 0.60 0.78 1.31 0.53 0.51 0.48 0.24
L30 5048–5054 14–35 19 1.21 1.02 0.78 1.44 0.79 0.48 27.11 15.66 57.23 0.37 0.58 0.41 0.55 0.55 0.55 0.74 0.23
L30 5062.35 14–33 18 1.32 0.96 0.82 1.97 0.72 0.31 29.24 15.32 55.44 0.28 0.64 0.60 1.72 0.45 0.76 0.74 0.16
L30 5074–5078 14–35 23 1.34 1.22 0.58 1.68 0.92 0.41 30.47 14.43 55.10 0.32 0.55 0.86 1.87 0.48 0.56 0.83 0.20
TELG   13–29 21 1.57 1.36 1.17 1.54 0.50 0.33 35.08 20.25 44.67 0.36 0.31 0.46 0.54 0.60 2.02 0.34 0.16
TELG   13–30 23 1.30 1.30 1.13 1.82 0.99 0.65 21.89 20.94 57.17 0.36 0.53 0.56 0.63 0.69 1.78 0.35 0.18
TELG   13–30 21 1.26 1.33 1.18 1.89 0.73 0.42 45.83 17.02 37.15 0.44 0.45 0.38 0.56 0.49 1.60 0.32 0.16
TELG   13–30 19 1.29 1.30 1.88 2.06 0.51 0.30 30.41 22.50 47.09 0.41 0.42 0.31 0.54 0.46 2.12 0.36 0.13
Open in a new tab

4.3.1. Straight Chain Alkanes

The carbon number of n-alkanes in Taodonggou group source rocks in Taibei sag ranges from nC13 to nC40, with the main peaks of nC17, nC18, nC19, nC21, nC23, and nC29. The short chains and ratio (∑C21–/∑C22+) range from 0.3 to 2.26, with an average value of 1.009. The carbon preference index (CPI) ranged from 1.05 to 1.57, with an average value of 1.294. The odd–even predominance index (OEP) ranged from 0.78 to 1.42, with an average value of 1.145 (Figure 7).

Figure 7.

Figure 7

Open in a new tab

Mass spectrometric analysis of n-alkanes (m/z 85) in saturated hydrocarbon components of Taodonggou group source rocks: (a) L-30 well, (b) YT-1 well, and (c) TELG profile.

4.3.2. Isoprenoids

Pristane (Pr) and phytane (Ph) can indicate the input and depositional environment of organic matter and are widely used parameters in isopren-like alkanes.14,15 The distribution of Pr/Ph of Taodonggou group source rocks in the study area ranges from 0.94 to 2.93, with an average value of 1.546, that of Pr/nC17 ranges from 0.17 to 1.08, with an average value of 0.574, and that of Ph/nC18 ranges from 0.25 to 0.46, with an average value of 0.345.

4.3.3. Terpanes

On the m/z = 191 mass chromatogram (Figure 8), terpenoids were mainly composed of gammacerane, moretane, homohopanes (C31–C35), 17α(H)-trisnorhopane (Tm), 18α(H)-trisnorhopane (Ts), tricyclic terpanes, tetracyclic terpane, and pentacyclic terpanes. The relative content of homohopanes is a positive sequence, that is, C31 > C32 > C33 > C34 > C35 homohopane, especially, C34 homohopane and C35 homohopane are very low.

Figure 8.

Figure 8

Open in a new tab

Mass spectrometric analysis of terpanes (m/z 191) in saturated hydrocarbon components of Taodonggou group source rocks: (a) L-30 well, (b) YT-1 well, and (c) TELG profile.

The abundance of C30 hopane is higher than that of C29 hopane in all samples, and the C29/C30 hopane ratio ranges from 0.32–0.83 (Table 3), with an average value of 0.53. The ratio of C19/C23 tricyclic terpane, C20/C23 tricyclic terpane, and C24/C23 tricyclic terpane ranges from 0.31 to 1.04 (average = 0.66), 0.44 to 1.87 (average = 1.04), and 0.46 to 0.76 (average = 1.04), respectively. The ratio of Ts/Tm ranges from 0.3 to 2.12 (average = 0.89) and that of YT1 and L30 wells show low values (0.3–0.76, with an average value of 0.53, less than 1), indicating that the organic matter of YT1 and L30 wells is in the mature stage; however, the ratio of the Ts/Tm value of the TELG profile ranges from 1.6 to 2.12 (average = 1.88), which indicates that the organic matter of the TELG profile is in the immature–mature stage16 (Table 3).

Gammacerane is present in all Taodonggou samples (Figure 8 and Table 3), and the gammacerane index (GI) ranges between 0.13 and 0.76, with an average value of 0.25. This suggests syn-depositional water column salinity stratification.17

4.3.4. Steroids

All samples of Taodonggou group in Taibei sag share similar sterane distribution patterns. Cholestane series compounds outsize pregnane series compounds. The distributions of regular steranes C27–C28–C29 show asymmetrical V-shaped and reverse L-shaped features in all samples (Figure 9). The relative proportion of αααC29sterane (R) is the highest (37.15–64.22% with an average value of 51.11%), followed by C27 (21.41–45.83% with an average value of 31.54%) and C28 steranes (13.52–22.5% with an average value of 17.35%).

Figure 9.

Figure 9

Open in a new tab

Mass spectrometric analysis of f sterane (m/z 217) in saturated hydrocarbon components of Taodonggou group source rocks: (a) L-30 well, (b) YT-1 well, and (c) TELG profile.

The ratio of C29ααα20S/(20S + 20R) sterane isomerization ranges from 0.28 to 0.49, while that of C29ββ/(ββ + αα) sterane isomerization varies from 0.31 to 0.64 (Table 3), which indicate a high thermal maturity.18

5. Discussion

The characteristics of organic petrology and organic geochemistry are of great importance to the evaluation of hydrocarbon generation potential of source rocks.19 Therefore, it is necessary to analyze and further reveal the abundance, type, maturity, parent material sedimentary environment of source rocks, and the influence of the parent material sedimentary environment on the occurrence of organic matter.

5.1. Organic Matter Evaluation

5.1.1. Abundance

Organic matter abundance is the material basis of hydrocarbon formation in source rocks, and it is also the most basic parameter to evaluate the quality of source rocks.20 The parameters commonly used to evaluate the organic matter abundance of source rocks are total organic carbon content (TOC), total hydrocarbon content (HC), hydrocarbon generation potential (PG), and chloroform asphalt A.21−23

According to the total organic carbon (TOC) and hydrocarbon generation potential (PG), Taodonggou group source rocks are mainly distributed in poor to excellent source rocks, in which poor source rocks account for 2.56%, good source rocks account for 28.21%, very good source rocks account for 5.15%, and excellent source rocks account for 61.54% (Figure 10a,c). According to the total organic carbon (TOC) and chloroform asphalt A, the source rocks of Taodonggou group in the study area are mainly distributed in good to excellent source rocks, with good source rocks accounting for 9.52%, very good source rocks accounting for 23.82%, and excellent source rocks accounting for 66.67% (Figure 10b,d). In conclusion, the source rocks of Taodonggou group in the study area are mainly excellent source rocks. This indicates that the source rocks of Taodonggou group in Taibei Sag have a good hydrocarbon generation potential.

Figure 10.

Figure 10

Open in a new tab

Evaluation of source rocks in Taodonggou group of Middle Permian: (a) cross plot of TOC and PG (modified after 22); (b) cross plot of TOC and chloroform asphalt A (modified after 20); (c) according to the cross plot of TOC and PG, the fan chart of hydrocarbon source rock grade is shown; and (d) according to the cross plot of TOC and chloroform asphalt A, the fan chart of hydrocarbon source rock grade is shown.

5.1.2. Type

The difference of organic matter types will affect the hydrocarbon generation potential and products of source rocks.21,24 There are many evaluation indexes of organic matter types, such as kerogen element composition, kerogen maceral composition and its type index, relative composition of steranes, and rock pyrolysis hydrogen index (HI)–oxygen index (OI).24−28

The cross plot of Tmax and HI (Figure 11a) shows that the organic matter types of Taodonggou group source rocks are mainly type III and types II–III, and some of them are type II and type I. In addition, kerogen macerals also show that the organic matter types of Taodonggou group source rocks are mainly type III and type II (Figure 11b), which are consistent with the results of Tmax and HI cross plot. It can be concluded that the organic matter types of Taodonggou group source rocks are mainly type III and types II–III. This indicates that the source rocks of Taodonggou group in Taibei sag have good gas and oil generation capacity.

Figure 11.

Figure 11

Open in a new tab

Types of organic matter in source rocks of Taodonggou group in Taibei sag: (a) cross plot of HI and Tmax (modified after 24) and (b) microcomponent triangulation (modified after 27).

5.1.3. Maturity

The maturity of organic matter is the key to generate a large amount of oil or natural gas. Ro and Tmax are important indicators of organic matter maturity.28−31 Previous studies have found that for continental mudstone, vitrinite reflectance (Ro) is the best index, followed by Tmax.29 However, Tmax can be used as a very good maturity index when organic matter types are III and II.29−31 Generally speaking, Ro < 0.5% or Tmax < 435 °C is the immature stage; 0.5% < Ro < 1.3% or 435 °C < Tmax < 455 °C is the oil window stage; 1.3% < Ro < 2% or 455 °C < Tmax < 475 °C is the condensate (wet gas) stage; and Ro > 2.0% or Tmax > 475 °C is the postmature (dry gas) stage.24,25,29

In an advanced analysis based on the intersection diagrams of Ro and TOC (Figure 12a), Tmax and TOC (Figure 12b) of Taodonggou group source rocks in the study area are drawn, respectively. The results suggest that the Middle Permian source rocks in Taibei sag are in the mature stage, most of them are distributed in the oil window stage, and a small amount are distributed in the condensate (wet gas) stage. This shows that the source rocks of Taodonggou group are mainly oil generating at present.

Figure 12.

Figure 12

Open in a new tab

Maturity of organic matter in source rocks of Taodonggou group in Taibei sag: (a) cross plot of TOC and Ro and (b) cross plot of TOC and Tmax.

5.2. Sedimentary Environment

5.2.1. Paleoclimate

Paleoclimate has an important influence on source rocks.32 Previous studies have found that the carbon preference index (CPI) of source rocks can indicate the degree of dryness and wetness of paleoclimate. Taking CPI = 1 as the boundary, the smaller the CPI value, the higher the degree of wetness.33−35 The CPI value of source rocks ranges from 1.05 to 1.57, with an average value of 1.294, which is similar to the CPI value of source rocks of Meishan formation in Yinggehai basin,34 and it is in a semihumid and semiarid climate, which is basically consistent with the previous results based on the annual ring of lignified stone.36 Therefore, Taodonggou source rock was formed in semihumid and semiarid environment.

5.2.2. Organic Matter Input

The main peak carbon of n-alkanes can indicate the input of organic matter.37−40 When the main peak carbon is low carbon number (<20), it indicates the source of algae and other lower aquatic organisms. When the carbon number is high (>C23), the distribution characteristics of the peak type indicate the input of terrestrial higher plants.38,39 The main carbon peaks of Taodonggou group source rocks in the study area are nC17, nC18, nC19, nC21, nC23, and nC29, indicating that the organic matter input of the source rocks is mixed source input, and the ratio ∑C21–/∑C22+ of source rocks can characterize the relative input of lower aquatic organisms and terrestrial higher plants.39 The ratio ∑C21–/∑C22+ of the source rocks ranges from 0.3 to 2.26 in the study area, with an average value of 1.009. It shows that the input amount of aquatic organisms is equal to that of terrestrial higher plants. According to the relationship between the ratio ∑C21–/∑C22+ and depth (Figure 13), it is found that the terrigenous higher plant input is dominant in the early stage of Taodonggou group, the lower aquatic organism input is dominant in the middle stage, and the terrigenous higher plant input is dominant in the late stage.

Figure 13.

Figure 13

Open in a new tab

Organic matter input from source rocks of Taodonggou group in Taibei sag.

The relative composition of C27, C28, and C29 regular steranes can reflect the source of organic matter input. Previous studies have found that C27 sterane indicates the source of aquatic organisms, C28 sterane is related to diatoms, and C29 sterane indicates the source of higher organisms.40−44 According to the regular sterane triangle of C27–C28–C29 (Figure 14), the source rocks of Taodonggou group are mainly distributed in estuarine bay and terrestrial, and a few are distributed in open marines. The corresponding biological sources are plankton and terrestrial higher plants.44 The results also show that the organic matter input of source rocks of Taodonggou group has the characteristics of a mixed source.

Figure 14.

Figure 14

Open in a new tab

Triangles of n-steranes (C27–C28–C29) in source rocks of Taodonggou group, Middle Permian (modified after 44).

In addition, tricyclic terpanes and tetracyclic terpanes are also important biomarkers of terrestrial organic matter input.42,43 It is generally believed that the higher the ratio of C19/C23 tricyclic terpane and C20/C23 tricyclic terpane, the higher the terrestrial organic matter input. The ratio of C19/C23 tricyclic terpane did not change significantly in the study area (vary from 0.15 to 1.04, with an average value of 0.66), which cannot prove that the source of organic matter is the mixed source. However, the ratio of C20/C23 tricyclic terpane changed obviously and has the characteristics of segmentation, which is basically consistent with the result expressed by the main peak carbon of n-alkanes.

In conclusion, the organic matter of source rocks of Taodonggou group is input as a mixed source. The early and late stage is dominated by terrestrial higher plants. The middle stage is dominated by lower aquatic organisms.

5.2.3. Redox Environment

Oxidation–reduction condition is one of the important factors affecting the preservation of organic matter, and the strength of reducibility determines the degree of destruction of organic matter by biochemical action.41,42 Previous studies have found that the ratio of pristane (Pr) to phytane (Ph) can indicate the oxidation–reduction environment: Pr/Ph < 0.8 indicates a strong reduction environment, 0.8 ≤ Pr/Ph < 3 indicates weak reduction and weak oxidation environments, and Pr/Ph ≥ 3 indicates the oxidation environment.41−44 The Pr/Ph source rocks of Taodonggou group in the study area mainly range from 0.94 to 2.93, with an average value of 1.546, which indicates that the source rocks in the study area are deposited in a weak reduction and weak oxidation environment.

In addition, Pr/nC17 and Ph/nC18 can be used to restore the properties of paleowater and indicate the type of kerogen.45 The intersection diagram of Pr/nC17 and Ph/nC18 (Figure 15) shows that the source rocks of Taodonggou group are deposited in a weak redox environment, which is a transitional environment. The results are basically consistent with Pr/Ph.

Figure 15.

Figure 15

Open in a new tab

Cross plot of Pr/nC17 and Ph/nC18 of Taodonggou group, Middle Permian (modified after 45).

5.3. Influence of Sedimentary Environment on Organic Matter Enrichment

The enrichment degree of organic matter depends on the content of original organic matter and preservation conditions.45−51 The content of original organic matter is mainly affected by the flourishing degree of Paleontology and the filling of terrigenous detritus, and these factors are closely related to the sedimentary environment. To explore the influence of the sedimentary environment on the enrichment of organic matter in Taibei sag, this study analyzed the paleoclimate, organic matter input, and oxidation–reduction conditions.

5.3.1. Influence of Paleoclimate on Organic Matter Enrichment

To explore the influence of paleoclimate on the abundance of organic matter, the relationship between CPI and TOC and PG and chloroform asphalt A is drawn (Figure 16). The results show that CPI has a weak negative correlation with TOC, PG, and chloroform asphalt A in the study area, which indicates that the warm and humid climate is conducive to the accumulation and preservation of organic matter, and the arid climate has an inhibitory effect on the occurrence of organic matter.

Figure 16.

Figure 16

Open in a new tab

Relationship between CPI and (a) TOC, (b) PG, and (c) chloroform asphalt A.

Previous studies52−55 have found that the warm and humid paleoclimate environment is conducive to the survival and reproduction of aquatic organisms and terrestrial higher organisms, and it will also cause the water body to deepen and form a reducing environment, which is conducive to the preservation of organic matter. On the contrary, the arid paleoclimate is not conducive to the survival and reproduction of aquatic organisms, which leads to the decline of organic matter abundance. In addition, the paleoclimate has a certain control effect on the input of terrigenous detritus.56 When the climate is humid, frequent precipitation makes a large number of provenance detritus fill, diluting the organic matter, which results in a less obvious relationship between the paleoclimate and organic matter abundance.

5.3.2. Influence of Organic Matter Input on Organic Matter Enrichment

The ∑C21–/∑C22 + and TOC, PG and chloroform asphalt A are plotted (Figure 17). The results showed that the contents of TOC, PG, and chloroform asphalt A were weakly positively correlated with ∑C21–/∑C22 +, which indicated that aquatic organisms were conducive to the enrichment and preservation of organic matter, and the contribution of aquatic organisms to the occurrence of organic matter was greater than that of terrestrial higher plants.

Figure 17.

Figure 17

Open in a new tab

Relationship between ∑C21–/∑C22 + and (a) TOC, (b) PG, and (c) chloroform asphalt A.

The abundance of organic matter depends not only on the development of organisms but also on the input of organic matter. The input of organic matter mainly comes from various aquatic organisms and terrestrial higher plants. The former is the main contributor to organic matter abundance, while the latter provides nutrition for the former.55,56

5.3.3. Influence of Redox Environment on Organic Matter Enrichment

The relationship between Pr/Ph and TOC, PG, and chloroform asphalt A was drawn (Figure 18). The results showed that the values of TOC, PG, and chloroform asphalt A increased with the increase of the Pr/Ph value in the study area. The results are different from the previous understanding of “reducing environment for the conservation of organic matter”. This shows that the oxidation–reduction environment has a certain control effect on the organic matter enrichment of Taodonggou group, but it is not the main control factor.

Figure 18.

Figure 18

Open in a new tab

Relationship between Pr/Ph and (a) TOC, (b) PG,and (c) chloroform asphalt A.

When the redox environment fluctuates, the abundance of organic matter changes greatly, and both redox environment and productivity will affect the preservation of organic matter.32 Although the climate of Middle Permian in Taibei sag is semiarid and semihumid, the climate is mainly warm and humid.36,57,58 Aquatic organisms and terrestrial higher organisms multiply in large numbers, forming high biological productivity. In addition, biological respiration can also increase oxygen consumption,59,60 and high deposition rate can reduce the time of organic matter oxidation and decomposition,60,61 which leads to the phenomenon of high concentration of organic matter in oxidation environment.

5.3.4. Enrichment Model of Organic Matter

Previous studies have found that the enrichment model of organic matter can be divided into three models: preservation model, productivity model, and productivity and anoxic interaction model.62−65 Compared with the productivity model, the abundance of organic matter in Taodonggou group source rocks is higher in partial oxidation environment and lower in partial reduction environment. To further discuss the organic matter enrichment mechanism of Taodonggou group source rocks in Taibei sag, the Taodonggou group source rocks are divided into early, middle, and late stages (Figure 19).

Figure 19.

Figure 19

Open in a new tab

Vertical variation trend of TOC, PG, chloroform asphalt A, CPI, Pr/Ph, and ∑C21–/∑C22 + in source rocks of Taodonggou group in the YT-1 well.

In the early stage, the paleoclimate was dry with less precipitation, which resulted in less input of terrigenous detritus and nutrients, a slow reproduction rate of aquatic organisms, and low productivity. The input of organic matter was mainly terrigenous higher plants. Although the water body was a partial reducing environment, the low productivity made the organic matter abundance of the source rocks low (Figure 20a). In the middle stage, the paleoclimate gradually became warm and humid, which was conducive to the reproduction of terrestrial higher plants. In addition, precipitation accelerated the weathering of parent rocks, intensified the input of terrigenous detritus and nutrients, promoted the reproduction of aquatic organisms, and gave high biological productivity. Precipitation made the sedimentary water deeper, and the whole was in a partial oxidation environment, However, the high productivity makes the organic matter abundance of source rocks in this stage (Figure 20b). In the late stage, the paleoclimate became dry again and the productivity decreased, which resulted in the low abundance of organic matter in this stage. The above is the enrichment model of organic matter in Taodonggou group of Middle Permian in Taibei sag.

Figure 20.

Figure 20

Open in a new tab

Enrichment model of organic matter in source rocks of Taodonggou group in Taibei sag: (a) early and late stage of Taodonggou group and (b) middle stage of Taodonggou group (modified after 62–65).

6. Conclusions

Based on the analysis of the organic petrology, organic geochemistry, sedimentary environment of the Middle Permian Taodonggou group source rocks, the influence factors on the enrichment of organic matter were revealed, and the enrichment model was established in the study area. The following conclusions can be obtained:

  • (1)

    The organic macerals of Taodonggou group source rocks in Taibei sag are mainly the exinite and sapropelite formation, followed by inertinite, and vitrinite is the least. The vitrinite mainly is vitrodetrinite, and the exinite is mainly lamalginiite.

  • (2)

    The source rocks of Taodonggou group in Taibei sag are mainly excellent source rocks. The types of organic matter are mainly type III and types II–III, which are in the mature stage, mainly in the oil window stage, and have a good hydrocarbon generation potential.

  • (3)

    The source rocks of Taodonggou group in Taibei sag were formed in a semihumid and semiarid climate with weak reduction and weak oxidation environments. The organic matter was transported into the mixed source. The terrestrial higher plants dominated in the early and late stage, and the aquatic organisms dominated in the middle stage. Under the coaction of paleoclimate, organic matter input, and redox environment, the enrichment model of organic matter with high productivity and weak oxidation environment characteristics can also form excellent source rocks.

Acknowledgments

This study was supported by the Major National Science and Technology Project of China (grant nos. 2016ZX05066001-002, 2017ZX05064-003-001, and 2016zx05007) and the Science and Technology Projects of PetroChina (grant nos. 2019b-0601, 2019b-0602). The authors thank Key Laboratory of Natural Gas Accumulation, China, National Petroleum Corporation and Development and Turpan-Hami Oil Co. of CNPC for providing testing samples, and our colleagues for the beneficial suggestion.

The authors declare no competing financial interest.

References

  1. Zhu X. M.; Zhong D. K.; Yuan X. J.; Zhang H. L.; Zhu S. F.; Sun H. T.; Gao Z. Y.; Xian B. Z. Development of sedimentary geology of petroliferous basins in China. Pet. Explor. Dev. 2016, 43, 890–901. 10.1016/S1876-3804(16)30107-0. [DOI] [Google Scholar]
  2. Xu C. C.; Zou W. H.; Yang Y. M.; Duan Y.; Shen Y.; Luo B.; Ni C.; Fu X. D.; Zhang J. Y. Status and prospects of deep oil and gas resources exploration and development onshore China. J. Nat. Gas Geosci. 2018, 3, 11–24. 10.1016/j.jnggs.2018.03.004. [DOI] [Google Scholar]
  3. Li J. Z.; Tao X. W.; Bai B.; Huang S. P.; Jiang Q. C.; Zhao Z. Y.; Chen Y. Y.; Ma D. B.; Zhang L. P.; Li N. X.; Song W. Geological conditions, reservoir evolution and favorable exploration directions of marine ultra-deep oil and gas in China. Pet. Explor. Dev. 2021, 48, 60–79. 10.1016/S1876-3804(21)60005-8. [DOI] [Google Scholar]
  4. Guo X. S.; Hu D. F.; Li Y. P.; Duan J. B.; Zhang X. F.; Fan X. J.; Duan H.; Li W. C. Theoretical Progress and Key Technologies of Onshore Ultra-Deep Oil/Gas Exploration.. Engineering 2019, 5, 458–470. 10.1016/j.eng.2019.01.012. [DOI] [Google Scholar]
  5. Fan D. L.; Li F. B.; Wang Z. L.; Miao Q.; Bai Y.; Liu Q. Y. Development status and prospects of China’s energy minerals under the target of carbon peak and carbon neutral. Chin. Min. Mag. 2021, 30, 1–8. [Google Scholar]
  6. Zou C. N.; Zhu R. K.; Chen Z. Q.; Ogg J. G.; Wu S. T.; Dong D. Z.; Qiu Z.; Wang Y. M.; Wang L.; Lin S. H.; Cui J. W.; Su L.; Yang Z. Organic-matter-rich shales of China. Earth-Sci. Rev. 2019, 189, 51–78. 10.1016/j.earscirev.2018.12.002. [DOI] [Google Scholar]
  7. Liang S. J. Achievements and potential of petroleum exploration in tuha oil and gas province. Xinjiang Pet. Geol. 2020, 41, 631–641. 10.7657/XJPG20200601. [DOI] [Google Scholar]
  8. Gang G.; Hao L.; Li H. M.; Jiao L. X.; Wang Z. Y.; Hou Q. Z. Organic geochemistry of Carboniferous and Lower Permian source rocks, Turpan-Hami Basin, NW China. Pet. Explor. Dev. 2009, 36, 583–592. 10.1016/S1876-3804(09)60147-6. [DOI] [Google Scholar]
  9. Sun M.; Gu W. P.; Liu Y.; Wang D. R.; Yang B. In Deep Seismic Acquisition Technology and Application Effect of pre Jurassic in Turpan Hami Basin, SPG/SEG Nanjing 2020 International Geophysical Conference 2020, Nanjing, China, 2020.
  10. Jiang S. H.; Li S. Z.; Somerville I. D.; Lei J. P.; Yang H. Y. Carboniferous–Permian tectonic evolution and sedimentation of the Turpan-Hami Basin, NW China: Implications for the closure of the Paleo-Asian Ocean. J. Asian Earth Sci. 2015, 113, 644–655. 10.1016/j.jseaes.2015.05.012. [DOI] [Google Scholar]
  11. Wali G.; Wang B.; Cluzel D.; Zhong L. L. Carboniferous – Early Permian magmatic evolution of the Bogda Range (Xinjiang, NW China): Implications for the Late Paleozoic accretionary tectonics of the SW Central Asian Orogenic Belt. J. Asian Earth Sci. 2018, 153, 238–251. 10.1016/j.jseaes.2017.07.045. [DOI] [Google Scholar]
  12. Shi Y. Q.; Ji H. C.; Yu J. W.; Xiang P. F.; Yang Z. B.; Liu D. D. Provenance and sedimentary evolution from the Middle Permian to Early Triassic around the Bogda Mountain, NW China: A tectonic inversion responding to the consolidation of Pangea. Mar. Pet. Geol. 2020, 114, 104169 10.1016/j.marpetgeo.2019.104169. [DOI] [Google Scholar]
  13. Li X. Q.; Zhong N. N.; Xiong B.; Wang T. G. Application of whole rock analysis in source rock research and comparison with kerogen analysis. Pet. Explor. Dev. 1995, 22, 30–40. [Google Scholar]
  14. Powell T. G.; Mckirdy D. M. Relationship between ratio of pristane to phytane, crude oil composition and geological environment in Australia. Nat. Phys. Sci. 1973, 243, 37–39. 10.1038/physci243037a0. [DOI] [Google Scholar]
  15. Peters K. E.; Molodowan J. M.. The Biomarker Guide: Interpreting Molecular Fossils in Petroleum and Ancient Sediments; Prentice Hall: New Jersey, 1993. [Google Scholar]
  16. Moldowan J. M.; Sundararaman P.; Schoell M. Sensitivity of biomarker properties to depositional environment and/or source input in the Lower Toarcian of SW-Germany. Org. Geochem. 1986, 10, 915–926. 10.1016/S0146-6380(86)80029-8. [DOI] [Google Scholar]
  17. Damsté J. S. S.; Kenig F.; Koopmans M. P.; Köster J.; Schouten S.; Hayes J. M.; Leeuw J. W. Evidence for gammacerane as an indicator of water column stratification. Geochim. Cosmochim. Acta 1995, 59, 1895–1900. 10.1016/0016-7037(95)00073-9. [DOI] [PubMed] [Google Scholar]
  18. Peters K. E.; Moldowan J. M.; Sundararaman P. Effects of hydrous pyrolysis on biomarker thermal maturity parameters: Monterey Phosphatic and Siliceous members. Org. Geochem. 1990, 15, 249–265. 10.1016/0146-6380(90)90003-I. [DOI] [Google Scholar]
  19. Xu X. F.; Xu S. H.; Liu J.; Chen L.; Liang H. R.; Mei L. F.; Liu Z. Q.; Shi W. Z. Thermal maturation, hydrocarbon generation and expulsion modeling of the source rocks in the Baiyun Sag, Pearl River Mouth Basin, South China Sea. J. Pet. Sci. Eng. 2021, 205, 108781 10.1016/j.petrol.2021.108781. [DOI] [Google Scholar]
  20. Chen J. P.; Zhao C. Y.; He Z. H. Discussion on evaluation criteria for hydrocarbon generation potential of organic matter in coal measures. Pet. Explor. Dev. 1997, 24, 1–5. [Google Scholar]
  21. Tissot B. P.; Welte D. H.. Petroleum Formation and Occurrence: A New Approach to Oil and Gas Exploration; Springer-Verlag, 1978. [Google Scholar]
  22. Makeen Y. M.; Abdullah W. H.; Hakimi M. H.; Mustapha K. A. Source rock characteristics of the Lower Cretaceous Abu Gabra Formation in the Muglad Basin, Sudan, and its relevance to oil generation studies. Mar. Pet. Geol. 2015, 59, 505–516. 10.1016/j.marpetgeo.2014.09.018. [DOI] [Google Scholar]
  23. Ahmed N.; Siddiqui N. A.; Rahman A. H. B. A.; Jamil M.; Usman M.; Sajid Z.; Zaidi F. K. Evaluation of hydrocarbon source rock potential: Deep marine shales of Belaga Formation of Late Cretaceous-Late Eocene, Sarawak, Malaysia. J. King Saud Univ., Sci. 2021, 33, 101268 10.1016/j.jksus.2020.101268. [DOI] [Google Scholar]
  24. Mani D.; Patil D. J.; Dayal A. M.; Prasad B. N. Thermal maturity, source rock potential and kinetics of hydrocarbon generation in Permian shales from the Damodar Valley basin, Eastern India. Mar. Pet. Geol. 2015, 66, 1056–1072. 10.1016/j.marpetgeo.2015.08.019. [DOI] [Google Scholar]
  25. Goodarzi F.; Haeri-Ardakani O.; Gentzis T.; Pedersen P. K. Organic petrology and geochemistry of Tournaisian-age Albert Formation oil shales, New Brunswick, Canada. Int. J. Coal Geol. 2019, 205, 43–57. 10.1016/j.coal.2019.01.015. [DOI] [Google Scholar]
  26. Khan I.; Zhong N. N.; Luo Q. Y.; Ai J. Y.; Yao L. P.; Luo P. Maceral composition and origin of organic matter input in Neoproterozoic–Lower Cambrian organic-rich shales of Salt Range Formation, upper Indus Basin, Pakistan. Int. J. Coal Geol. 2020, 217, 103319 10.1016/j.coal.2019.103319. [DOI] [Google Scholar]
  27. Cao Q. Y. Identification of microcomponents and types of kerogen under transmitted light. Pet. Explor. Dev. 1985, 12, 14–23. [Google Scholar]
  28. Gao J. L.; Ni Y. Y.; Li W.; Yuan Y. L. Pyrolysis of coal measure source rocks at highly to over mature stage and its geological implications. Pet. Explor. Dev. 2020, 47, 773–780. 10.1016/S1876-3804(20)60092-1. [DOI] [Google Scholar]
  29. Kumar S.; Das S.; Bastia R.; Ojha K. Mineralogical and morphological characterization of Older Cambay Shale from North Cambay Basin, India: Implication for shale oil/gas development. Mar. Pet. Geol. 2018, 97, 339–354. 10.1016/j.marpetgeo.2018.07.020. [DOI] [Google Scholar]
  30. Radke M.; Welte D. H.; Willsch H. Maturity parameters based on aromatic hydrocarbons: Influence of the organic matter type. Org. Geochem. 1986, 10, 51–63. 10.1016/0146-6380(86)90008-2. [DOI] [Google Scholar]
  31. Liu B.; Liang D.; Jie F.; Jia R.; Fu J. Organic Matter Maturity and Oil/Gas Prospects in Middle-Upper Proterozoic and Lower Paleozoic Carbonate Rocks in Northern China. Chin. J. Geochem. 1986, 5, 55–70. 10.1007/BF02872062. [DOI] [Google Scholar]
  32. Wu W.; Liu W. Q.; Mou C. L.; Liu H.; Qiao Y.; Pan J. N.; Ning S. Y.; Zhang X. X.; Yao J. X.; Liu J. D. Organic-rich siliceous rocks in the upper Permian Dalong Formation (NW middle Yangtze): Provenance, paleoclimate and paleoenvironment. Mar. Pet. Geol. 2021, 123, 104728 10.1016/j.marpetgeo.2020.104728. [DOI] [Google Scholar]
  33. Li C. L.; Ma S. P.; Xia Y. Q.; He X. B.; Gao W. Q.; Zhang G. Q. Assessment of the relationship between ACL/CPI values of long chain n-alkanes and climate for the application of paleoclimate over the Tibetan Plateau. Quat. Int. 2020, 544, 76–87. 10.1016/j.quaint.2020.02.028. [DOI] [Google Scholar]
  34. Xu J. Y.; Niu Y. B.; Xu S. K.; Zhao X. W. Main controlling factors and development model of the Miocene marine source rocks in Yinggehai basin. Bull. Geol. Sci. Technol. 2021, 40, 54–63. 10.19509/j.cnki.dzkq.2021.0206. [DOI] [Google Scholar]
  35. Luo P.; Peng P. G.; Lü H.; Zheng Z.; Wang X. Latitudinal variations of CPI values of long-chain n-alkanes in surface soils: Evidence for CPI as a proxy of aridity. Sci. China: Earth Sci. 2012, 55, 1134–1146. 10.1007/s11430-012-4401-8. [DOI] [Google Scholar]
  36. Wei X. X.; Zhang X. H.; Huang X.; Luan T. F. Palaeoclimate reconstruction of Middle Permian in Tuha basin: evidence from the fossil wood growth rings. Earth Sci. 2016, 41, 1771–1780. [Google Scholar]
  37. Bohacs K. M.; Grabowski G. J. Jr.; Carroll A. R.; Mankiewicz P. J.. Production, Destruction, and Dilution—The Many Paths to Source-Rock Development 2005, 82, 61–101..
  38. Huang B. C.; Zhou Y. X.; Zhu R. X. Discussions on Phanerozoic evolution and formation of continental China, based on paleomagnetic studies. Earth Sci. Front. 2008, 15, 348–359. 10.1016/S1872-5791(08)60068-8. [DOI] [Google Scholar]
  39. Requejo A. G.; Hieshima G. B.; Hsu C. S.; McDonald T. J.; Sassen R. Short-chain (C21 and C22) diasteranes in petroleum and source rocks as indicators of maturity and depositional environment. Geochim. Cosmochim. Acta. 1997, 61, 2653–2667. 10.1016/S0016-7037(97)00106-3. [DOI] [Google Scholar]
  40. Tan Z. Z.; Lu S. F.; Li W. H.; Zhang Y. Y.; He T. H.; Jia W. L.; Peng P. A. Climate-driven variations in the depositional environment and organic matter accumulation of lacustrine mudstones: Evidence from organic and inorganic geochemistry in the Biyang Depression, Nanxiang Basin. China. Energy Fuels 2019, 33, 6946–6960. 10.1021/acs.energyfuels.9b00595. [DOI] [Google Scholar]
  41. Sachsenhofer R. F.; Popov S. V.; Akhmetiev M. A.; Bechtel A.; Gratzer R.; Gross D.; Horsfield B.; Rachetti A.; Rupprent B.; Schaffar W. B. H.; et al. The type section of the Maikop Group (Oligocene-Lower Miocene) at the Belaya River (North Caucasus): depositional environment and hydrocarbon potential. AAPG Bull. 2017, 101, 289–319. 10.1306/08051616027. [DOI] [Google Scholar]
  42. Seifert W. K.; Moldowan J. M. Use of biological makers in petroleum exploration. Methods Geochem. Geophys. 1986, 24, 261–290. [Google Scholar]
  43. Gelpi E.; Schneider H.; Mann J.; Oró Hydrocarbons of geochemical significance in microscopic algae. Phytochemistry 1970, 9, 603–612. 10.1016/S0031-9422(00)85700-3. [DOI] [Google Scholar]
  44. Huang W. Y.; Meinschein W. G. Sterols as ecological indicators. Geochim. Cosmochim. Acta 1979, 43, 739–745. 10.1016/0016-7037(79)90257-6. [DOI] [Google Scholar]
  45. Connan J.; Cassou A. M. Properties of gases and petroleum liquids derived from terrestrial kerogen at various maturation levels. Geochim. Cosmochim. Acta 1980, 44, 1–23. 10.1016/0016-7037(80)90173-8. [DOI] [Google Scholar]
  46. Bohacs K. M.; Grawbowski G. J.; Carroll A. R.; Mankeiwitz P. J.; Miskell-Gerhardt K. J.; Schwalbach J. R.; Wegner M. B.; Simo J. A. Production, destruction, and dilution-the many paths to source-rock development. SEPM Spec. Publ. 2005, 82, 61–101. [Google Scholar]
  47. Adams D.; Hurtgen M.; Sageman B. Volcanic triggering of a biogeochemical cascade during Oceanic Anoxic Event 2. Nat. Geosci. 2010, 3, 201–204. 10.1038/ngeo743. [DOI] [Google Scholar]
  48. Ji W. M.; Hao F.; Song Y.; Tian J. Q.; Meng M. M.; Huang H. X. Organic geochemical and mineralogical characterization of the lower Silurian Longmaxi shale in the southeastern Chongqing area of China:Implications for organic matter accumulation. Int J. Coal Geol. 2020, 220, 103412 10.1016/j.coal.2020.103412. [DOI] [Google Scholar]
  49. Xu H.; Xie Q. L.; Wang S. M.; Yu S. Organic geochemical characteristics and gas prospectivity of Permian source rocks in western margin of Songliao Basin, northeastern China. J. Pet. Sci. Eng. 2021, 205, 108863 10.1016/j.petrol.2021.108863. [DOI] [Google Scholar]
  50. Passey Q. R.; Bohacs K.; Esch W. L.; Klimentidis R.; Sinha S. In From Oil-Prone Source Rock to Gas-Producing Shale Reservoir - Geologic and Petrophysical Characterization of Unconventional Shale Gas Reservoirs, SPE-131350, CPS/SPE International Oil & Gas Conference and Exhibition in China, Beijing, China., 2010.
  51. Hu T.; Pang X. Q.; Jiang S.; Wang Q. F.; Xu T. W.; Lu K.; Huang C.; Chen Y. Y.; Zheng X. W. Impact of Paleosalinity, Dilution, Redox, and Paleoproductivity on Organic Matter Enrichment in a Saline Lacustrine Rift Basin: A Case Study of Paleogene Organic-Rich Shale in Dongpu Depression, Bohai Bay Basin, Eastern China. Energy Fuels 2018, 32, 5045–5061. 10.1021/acs.energyfuels.8b00643. [DOI] [Google Scholar]
  52. Liang H. R.; Xu G. S.; Xu F. H.; Yu Q.; Liang J. J.; Wang D. Y. Paleoenvironmental evolution and organic matter accumulation in an oxygen-enriched lacustrine basin: A case study from the Laizhou Bay Sag, southern Bohai Sea (China). Int. J. Coal Geol. 2019, 217, 103318 10.1016/j.coal.2019.103318. [DOI] [Google Scholar]
  53. Fang Z.; Pu X. G.; Chen S. R.; Yan J. H.; Han W. Z.; Shi Z. N.; Zhang W.; Chen X. R.; Dong Q. M. Investigation of enrichment characteristic of organic matter in shale of the 2nd member of Kongdian formation in Cangdong sag. J. Chin. Univ. Min. Technol. 2021, 50, 304–317. [Google Scholar]
  54. Ma Y. Q.; Fan M. S.; Lu Y. C.; Liu H. M.; Hao Y. Q.; Xie Z. H.; Liu Z. H.; Peng L.; Du X. B.; Hu H. Y. Climate-driven paleolimnological change controls lacustrine mudstone depositional process and organic matter accumulation: Constraints from lithofacies and geochemical studies in the Zhanhua Depression, eastern China. Int. J. Coal Geol. 2016, 167, 103–118. 10.1016/j.coal.2016.09.014. [DOI] [Google Scholar]
  55. Yang W. Q.; Wang X. J.; Jiang Y. L.; Zhang S.; Wang Y.; Zhu D. Y.; Zhu D. S. Quantitative reconstruction of paleoclimate and its effects on fine-grained lacustrine sediments:A case study of the upper Es4 and lower Es3 in Dongying Sag. Pet. Geol. Recovery Effic. 2018, 25, 29–36. [Google Scholar]
  56. Cichon-Pupienis A.; Littke R.; Lazauskienė J.; Baniasad A.; Pupienis D.; Radzevičius S.; Šiliauskas L. Geochemical and sedimentary facies study – Implication for driving mechanisms of organic matter enrichment in the lower Silurian fine-grained mudstones in the Baltic Basin (W Lithuania). Int. J. Coal Geol. 2021, 244, 103815 10.1016/j.coal.2021.103815. [DOI] [Google Scholar]
  57. Liu L. J.; Yao Z. Q. Early Late Permian Flora from Turpan Hami Basin. Acta Palaeontol. Sin. 1996, 35, 644–677. [Google Scholar]
  58. Wu S. Z. Paleoclimate of lower Permian in Xinjiang. Xinjiang Geol. 1996, 14, 270–277. [Google Scholar]
  59. Soares A.; Berggren M. Indirect link between riverine dissolved organic matter and bacterioplankton respiration in a boreal estuary. Mar. Environ. Res. 2019, 148, 39–45. 10.1016/j.marenvres.2019.04.009. [DOI] [PubMed] [Google Scholar]
  60. Ding J. H.; Zhang J. C.; Shi G.; Shen B. J.; Tang X.; Yang Z. Z.; Li X. Q.; Li C. X. Sedimentary environment and organic matter enrichment mechanisms of the Upper Permian Dalong Formation shale,southern Anhui Province, China. Oil Gas Geol. 2021, 42, 158–172. [Google Scholar]
  61. Xue J.; Liu L. F.; Sun H. F.; Huang S. B.; Geng M.; Chen Y.; Li S. P.; Shen N. Differential distributin of high-qualiity lacustrine source rocks controlled by climate and tectonics: a case study from Bozhong sag. Acta Pet. Sin. 2019, 40, 165–175. 10.7623/syxb201902004. [DOI] [Google Scholar]
  62. Calvert S. E.; Fontugne M. R. On the Late Pleistocene - Holocene Sapropel Record of Climatic and Oceanographic Variability in the Eastern Mediter - ranean. Paleoceanography 2001, 16, 78–94. 10.1029/1999PA000488. [DOI] [Google Scholar]
  63. Sageman B. B.; Murphy A. E.; Werne J. P.; Straten C. A. V.; Hollander D. J.; Lyons T. W. A Tale of Shales: The Relative Roles of Production, Decomposition, and Dilution in the Accumulation of Organic-Rich Strata, Middle– Upper Devonian, Appa-lachian Basin. Chem. Geol. 2003, 195, 229–273. 10.1016/S0009-2541(02)00397-2. [DOI] [Google Scholar]
  64. Mort H.; Jacquat O.; Adatte T.; Steinmann P.; F?Llmi K.; Matera V.; Berner Z.; Stüben D. The Cenomanian/Turonian Anoxic Event at the Bonarelli Level in Italy and Spain: Enhanced Productivity and/or Better Preservation?. Cretaceous Res. 2007, 28, 597–612. 10.1016/j.cretres.2006.09.003. [DOI] [Google Scholar]
  65. Li W. H.; Lu S. F.; Tan Z. Z.; Taohua He T. H. Lacustrine Source Rock Deposition in Response to Coevolution of the Paleoenvironment and Formation Mechanism of Organic-Rich Shales in the Biyang Depression, Nanxiang Basin. Energy Fuels 2017, 31, 13519–13527. 10.1021/acs.energyfuels.7b02880. [DOI] [Google Scholar]

Articles from ACS Omega are provided here courtesy of American Chemical Society

RESOURCES