The
Chinese government is seeking CO2 gas emission reduction
measures. CO2 capture and geological sequestration is one
of the main measures. Injecting CO2 into oil reservoirs
can not only achieve the environmental protection purpose of CO2 geological sequestration but also improve oil recovery and
realize economic benefits, which helps to offset the cost of CO2 sequestration. Therefore, the oil reservoir is one of the
best sites for CO2 sequestration. As for the reservoir
of CO2 flooding after water flooding, there are two methods
for evaluating the potential of CO2 enhanced oil recovery
(EOR) and sequestration capacity, which are the mass balance method
and analogy method. Through a combination of these two methods, this
paper presents a new method, which can be reasonably used to evaluate
these potentials. Besides, the screening criteria of CO2 sequestration and EOR in the Junggar Basin are also proposed. On
the basis of the guidelines of CO2 source matching, reservoir
characteristics, and fluid characteristic, four typical low permeability
reservoirs (Caiman oil reservoir, Karamay oil reservoir, Beisantai
oil reservoir, and Luliang oil reservoir) of the Junggar Basin are
selected to study their potential of CO2 EOR and sequestration.
And then the potential of CO2 EOR and sequestration capacity
for the Junggar Basin oil reservoirs of CO2 flooding after
water flooding is studied by applying the method mentioned above.
For 275 development blocks of 24 oil fields in the Junggar Basin,
139 development blocks are suitable for CO2 miscible flooding
EOR and sequestration, whereas 136 development blocks are suitable
for CO2 immiscible flooding EOR and sequestration. The
total EOR potential could be 18 407.76 × 104 t and the CO2 sequestration potential could amount to
47 486.0 × 104 t. The evaluation results show
that the Junggar Basin’s oil reservoirs are suitable sites
for CO2 EOR and sequestration and have great potentials.
It can provide the decision basis for the future implementation of
CO2 emission reduction projects in Western China.
The technology of Stimulated reservoir volume (SRV) has been the key technology for unconventional reservoir development, it can create fracture network in formation and increase the contact area between fracture surface and matrix, thus realizing the three-dimensional stimulation and enhancing single well productivity and ultimate recovery. In China, the Ordos Basin contains large areas of tight oil reservoir with the porosity of 2~12 % and permeability of 0.01~1 mD. The most used development mode is conventional fracturing and water flooding, which is different from the natural depletion mode in oversea, but the development effect is still unfavorable. The idea of SRV is proposed in nearly two years in Changqing Oilfield. SRV measures are implemented in some old wells in tight oil formation. It is a significant problem that should be solved urgently about how to evaluate the volume fracturing effect.Based on the real cases of old wells with SRV measures, the microseismic monitoring is used to analyze the scale of formation stimulation and the complexity of fracture network after volume fracturing; the numerical well test and production data analysis (PDA) are selected to explain the well test data, to analyze the dynamic data, and to compare the changes of formation parameters, fluid parameters and plane streamlines before and after volume fracturing; then the interpretation results of well test with the dynamic of oil and water wells are combined to evaluate the stimulation results of old wells after SRV. This paper has presented a set of screening criteria and an evaluation method of fracturing effect for old well with SRV in tight oil reservoir. It will be helpful to the selection of candidate well and volume fracturing operation in Ordos Basin tight oil reservoir.It should be noted that the evaluation method mentioned in the paper can be expanded to volume stimulation effect evaluation in other unconventional reservoirs, such as tight gas, shale gas and so on.
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