延长油田为超低渗透油藏，储层渗透率低，纳米级孔喉占比高，孔喉结构复杂，地层水矿化度高、Ca2+质量浓度高，CO2-地层水-岩石和CO2-原油作用对该类储层物性及赋存流体性质的影响更复杂。为此，基于化子坪、乔家洼和白豹三个CO2驱油示范区，针对性开展了上述两种作用的影响规律研究。结果表明，CO2长期注入对超低渗透油藏储层物性及流体性质具有较大影响。水岩反应后，岩心孔隙度、渗透率和接触角均下降，且下降幅度随注入压力升高均呈先增大后降低的规律，HCO3-和Ca2+质量浓度随压力升高均呈先增大后稳定的态势；实际注气压力下，三个示范区岩心总体堵塞率分别为7.71%，8.65%和13.88%，且小孔隙堵塞更为严重，其堵塞率分别达到21.36%，26.66%和32.81%。受CO2-原油作用影响的岩心孔隙度和渗透率呈现与水岩反应条件下相似的变化规律；注入压力升高，采出油中C3~C14和C15~C29含量增加，C30+和沥青质含量降低，原油黏度对应迅速降低，且各组分和原油黏度在达到混相压力后稳定；实际注气压力下，岩心堵塞率分别为15.81%，18.85%和20.69%，并以中小孔隙堵塞为主，由于混相条件CO2-原油作用更强，该类孔隙中白豹示范区岩心堵塞率较化子坪和乔家洼分别高20.84%和11.92%。
The Yanchang oilfield is an ultra-low permeability reservoir with low matrix permeability, high proportion of nanoscaled pore throats, complex pore-throat structures, high salinity of formation water, and high mass concentration of Ca2+. The interactions among CO2-formation water-rock and CO2-crude oil exert more complex impacts on reservoir properties and fluid characteristics in such reservoirs. Targeted studies were conducted at three CO2 flooding areas （Huaziping, Qiaojiawa, and Baibao） to investigate these interaction mechanisms. The results showed that long-term CO2 injection significantly affected the reservoir properties and fluid characteristics in ultra-low permeability reservoirs. Due to the water-rock interaction, the core porosity, permeability, and contact angle were all decreased, with the magnitude of decrease initially increasing then decreasing as injection pressure was raised. Meanwhile, with the increase of pressure, the mass concentrations of HCO3- and Ca2+ increased and then reached a plateau. Under actual injection pressures, the overall core blockage rates in the three tested areas were 7.71%, 8.65%, and 13.88%, respectively, with more severe plugging observed for smaller pores （corresponding blockage rates were 21.36%, 26.66% and 32.81%）. The porosity and permeability under the influence of CO2-crude oil interaction showed similar trends to those under water-rock interaction. Increasing injection pressure enhanced the C3-C14 and C15-C29 components but reduced the C30+ fractions and asphaltene content in produced oil, so the viscosity of crude oil correspondingly decreased rapidly. After the minimum miscible pressure was reached, the composition and the viscosity of crude oil became unchanged. Under actual injection pressures, the core blockage rates were 15.81%, 18.85% and 20.69%, respectively, with blockage predominantly in medium and small pores. Under miscible conditions, the core blockage rate in Baibao area in these pores was 20.84% and 11.92% higher than those in Huaziping and Qiaojiawa, respectively, reflecting stronger CO2-oil interactions during miscible flooding.
