Research On Relation Between Fault System And CO₂ Gas Reservoir Formation In Songliao Basin

By using previous seismic data and studying geometry characteristics of faults in Songliao basin, kinematic features of faults were analyzed systematically combining with sand-box analog model and balanced cross section, and fault formation and active stages were determined. Taking Xujiaweizi fault depression, Changling fault depression and southeast uplift as working area, strata-dissecting features of faults were separated and distribution law of fault in different stage was clearly understood. There are 4 types of faults in Songliao basin: lithosphere fault, crustal fault, basement fault and cap rock fault. Lithosphere fault and crustal fault are called deep fault. Deep faults interpreted by gravity and magnetic are mostly magma upwelling channels. This paper summarized 3 kinds of basement faults with different activity laws: basement fault faulting in faulted period (I-BF), basement fault faulting in faulted period and depression period (I-II-BF), and basement fault faulting in faulted period, depression period and inversion period (I-II-III-BF). Faults that controlled CO₂ gas reservoir mostly are basement faults which are relatively large-scale, controlling-depression, being volcanic rock upwelling channel, converging downward to detachment zone and connecting with deep faults (magma channels). Based on these four principles, the distribution of basement faults that possibly controlled CO₂ gas reservoir was determined.According to CO₂ gas content, layer series and plane distribution characteristics, the distribution laws and control factors of CO₂ gas in Songliao basin were summarized.Based on the division of fault system, determination of controlling-reservoir fault types and distribution law of CO₂ gas, the control effect of deep faults and controlling-reservoir faults on the formation and evolution of CO₂ gas reservoir was analyzed comprehensively. The favorable area for the accumulation of CO₂ gas was predicted combining with formation mechanism of CO₂ gas reservoir and distribution of volcanic rock bodies.On the basis of the results above, accumulation model of CO₂ gas reservoir was established: deep fault creeping-shallow ancient volcanic channel infill injection mode, deep fault creeping-shallow fault and ancient volcanic channel congruent infill injection mode and major fault in reverse basement infill injection mode.