| carbonated water injection |
carbonated water injection
is the simplest way of supplying
CO2 to reservoirs and involves the injection of water saturated
with CO2 to the maximum of (3–5 wt %) |
displacement of oil by carbonated
water is accompanied by a
significant lag of the front of the concentration of CO2 in water from the front of oil displacement, which depends on the
distribution coefficient of CO2 between oil and water,
its concentration in water, as well as the pressures and temperatures
of the reservoir conditions; this leads to a significant increase
in the time taken to obtain beneficial effects from the use of technology |
relatively low consumption of CO2 (6–7 times less) during injection into the
reservoir compared to other techniques |
low permeability
or moderately homogeneous reservoirs are the
only suitable candidates for this process |
| continuous CO2 injection in the gaseous
phase |
this method is widely used to displace
residual
oil in a flooded reservoir by continuous injection of carbon dioxide |
it achieves a higher oil displacement ratio than
other CO2 technologies; this is due to the fact that in
front of the advancing front of CO2 an oil swell is formed,
which is characteristic of processes with miscible displacement |
rapid breakthroughs of CO2 to production wells through
highly permeable formations, gravity separation, and significant reduction
in sweep efficiency are possible |
after
primary recovery, this technique is suitable
for reservoirs with light to medium gravity oil and those that are
highly flooded or strongly water-wet |
| displacement
of oil by CO2 alone requires large
expenditures |
| cyclic injection of CO2 into injection wells |
this method makes it possible
to develop low-permeability,
heterogeneous reservoirs by cyclic injection of CO2; this
improves upon continuous CO2 injection which tends to be
less effective, more costly, and impractical |
it is possible
to increase both the coefficient of oil displacement
by CO2 and the coefficient of reservoir sweep, as well
as to minimize the risk of gas breakthrough into the producing wells |
displacement of oil by CO2 alone requires large
expenditures |
suitable for reservoirs exhibiting different
zones of permeability. |
| injection of mixtures
of captured flue gases |
compositions of flue gases vary
but typically include air-polluting
components, some of which including CO2 could be captured |
flue gases are low cost to obtain, and their sequestration
would serve to reduce air pollution of the environment |
gases other than CO2 mix well only with lighter
crude oils |
strong dependence of the displacement of
oil by gaseous CO2 slugs on the conditions of gravity separation
limits the
use of this technology in reservoirs with high vertical permeability. |
| alternating injection of CO2 and water |
by injecting the required volume
of CO2 in small portions, alternately or simultaneously
with water, a higher
efficiency of CO2 EOR can be achieved; in this case, the
duration between cycles depends on the density of the well spacings
and patterns of injectors and producers; that duration can vary from
several hours to a month or more |
effective
way of enhancing oil recovery for low-permeability
oil reservoirs |
low permeability and poor pore space
connectivity in some reservoirs
limit injection rates |
technology can be
applied as part of an existing
reservoir pressure maintenance system and used both at individual
wells and/or across an entire reservoir involving multiple wells |
| in heterogeneous formations with high crude oil
viscosity,
the quantities of water and gas injected should be lower |
| surface equipment toggling between CO2 and
water
injection is required |
| CO2-foam injection technology |
these
methods are based on the use of foams, a
process that controls the movement of CO2 by generating
foam (dispersing CO2 in a liquid phase) |
use
of foam helps to achieve better oil displacement compared
to waterflooding or the above CO2 injection technologies |
CO2-foam injection technology is a lengthy process |
this technology is suitable for highly heterogeneous
reservoirs with some highly permeable/porous layers and some oil-depleted
zones with high water saturations |
| the method
reduces the gravitational separation of fluids and
stabilizes the displacement front |
composition of the
surfactant is likely to be unstable under
harsh reservoir conditions |
| foaming surfactant
solutions more strongly reduce the relative
permeability of the pore space for gas than water; foam surfactant
properties can be improved with NP additives |
possibility
exists for superficial absorption of the foams
by the reservoir rocks; moreover, in some reservoirs, the surfactant
around CO2 bubbles might not be effective as foam flows
through constricted pore throats |
| gas-cyclic injection and production through the
same wellbores (“huff-n-puff” process) |
this involves the injection of CO2 directly
into a production well with its subsequent shutdown for soaking the
bottom hole formation zone and subsequent oil production |
this technology can significantly reduce capital costs for
the implementation of the technology since it does not require the
construction of special injection wells |
asphaltene dropout |
injection of CO2 under supercritical
conditions is suitable for deep low-permeability reservoirs and those
associated with water drives |
| this method makes it possible to implement the
delivery of liquefied CO2 by road, which can be a more
profitable option in some cases |
possible equipment corrosion |
| need to separate and capture recycled CO2 from oil
and associated gas ultimately produced |
| stability
of equipment seals |
