Geological Assessment And Risk Analysis In CO₂ Geological Sequestration

CO2 geological sequestration is one method by injecting the captured CO2 into closed natural underground pore formation and sealing it in the underground closure reservoir,so as to achieve the purpose of reducing CO2 emissions,which is one of the most effective ways for decreasing CO2 emission.The power of CO2 flooding/migration during the process of CO2 geological sequestration is overpressure and buoyancy,but in some cases the CO2 leakage may happen,the leaking-out way is CO2 leaks through the layer which is weaker among upper barrier,lower barrier and the lateral barrier.After performed analysis the data of Logging,drilling and completion,rock-electricity test etc about 293 wells,this study shows detailed descriptions for reservoir layer C6,caprock layer C4+5 by structure,deposition,reservoir structure property,physical property,and pore structure property and etc technology,This study also performs total evaluation for cap layer closure ability and establishes 3D geological model for CO2 geological sequestration.A conceptual 3D-model which established for studying the effects of cap layer to CO2 geological sequestration,the simulated result shows:when the permeabilityof the cap layer is low,the up-moving of the CO2 will be very slow,and the capability of sealing will be good.While when the permeability of cap layer is high,the capability of sealing will be bad.The statistical analysis shows:the geological structure of Yanchang formation is in balanced condition,fracture layer is not growing,and the deposition environment is deltaic plain,which mean the reservoir cap is good.The cap layer is mainly of physical closure and is a good environment for CO2 geological sequestration.Combined with known materials,the CO2 flooding has been stimulated to show what the oil production is after 15 years,and what 200-year CO2 movement is after CO2 flooding completed.It shows that:after 15-years CO2 flooding,it will be largely improved to Crude oil production between injection and production wells for the main layer C61 and C62,and the recovery ratio will be enhanced than water flooding by 10 percent.The saturation of CO2 is higher near the injecting wells within the layer C4+52 after CO2 geological sequestration for 200 years,but the volume of leakage is not very high,at same time high saturation of CO2 area seldom appears within the layer C4+51,the leakage is not obviously,it shows that we can implement the CO2 geological sequestration within the layer of C6 among JT203 well area.Yanchang formation is a monocline structural and its dip angle is about 0.5-1°,and its lateral seal is closed by stratigraphic lithology,and its sealing capability is controlled by sedimentary system,there is a certain risk of leakage through lateral barriers.So CO2 flooding is an effective production measure within C6 layer,but there is a certain risk of leakage during CO2 geological sequestration.