Research On Characteristics Of Reservoir Physical Properties Changes In Tight Sandstone Reservoir After CO₂ Flooding

CO₂ flooding technology is an effective method to improve the recovery of low-permeability oil and gas fields.In view of the changes in reservoir properties after CO₂ action,most of the research has focused on changes in ion concentration and changes in porosity and permeability.There are few studies on the changes of structure,capillary force curve,and reservoir micro-heterogeneity.In this paper,the tight sandstone of the third member of the Shaliu Formation in the Xiliu 10 fault block of the HB Oilfield is taken as the research object.The micro-pore structure,macro-pore structure and capillary force of the tight sandstone reservoir in the Xiliu10 fault block are investigated using low-temperature nitrogen adsorption experiments and high-pressure mercury intrusion experiments.The curve changes and micro-heterogeneity were analyzed before and after the CO₂ effect,and the influencing factors were analyzed.The main achievements and understanding are as follows:?1?Correspondence between the typical low-temperature N2 adsorption curve hysteresis loop shape and pore morphology of tight sandstone.It is found that most of the samples in this experiment are of type C,and a few are close to type B,indicating that the pore mesopores in the reservoir of Xiliu 10 fault block?2⁵0nm?The pores are mainly cylindrical with a high degree of opening,and there are crack-shaped pores.The specific surface area,average pore diameter and total pore volume of the reservoir pores after CO₂ action are slightly larger,but the most probable radius remains basically unchanged.?2?A high-pressure mercury intrusion test was carried out on the sample.The experimental results showed that the number of small pores in the range of 0.001 to0.1?m increased after CO₂,and the number of pores in the range of 0.1?m to 1?m decreased slightly.The quantity is basically unchanged,but the permeability contribution is still dominated by micron-sized pores.?3?After CO₂ action,the pore sand throat characteristic parameters and permeability of tight sandstone have changed.The overall realization is that the pore throat radius and connectivity are significantly improved and the capillary force curve moves to the lower left.?4?The concept of"heterogeneous index Q"is proposed to quantitatively characterize the microscopic heterogeneity of the reservoir.In this paper,the method of image processing analysis to study the heterogeneity of tight reservoirs is established.The self-edited Image J plug-in is used to accurately identify the faces of cast thin slices.Proposed a new parameter for quantitatively characterizing the microscopic pore heterogeneity of tight sandstones,namely the heterogeneity index Q,and the fractal dimension calculated by the liquid nitrogen adsorption experiment was used as the new parameter test,and the heterogeneity index Q was discussed.Geological significance.The results show that the heterogeneity index Q has a good positive correlation with the fractal dimension,and it can be considered that it has a good characterization effect on reservoir heterogeneity,pore throat distribution and pore surface roughness;The quality index Q has a good correlation with the physical property parameters,specific surface,average pore diameter and total pore volume of the sample,indicating that the heterogeneity index Q can well characterize the reservoir,quantitatively evaluate the reservoir,and The evaluation of reservoirs and the classification of reservoirs provide a new basis,which provides a new direction for the delineation of advantageous horizons in the later stage and guides the development and exploitation.The Q value of the microscopic heterogeneity index of the rock after CO₂ action becomes larger,indicating that the microscopic heterogeneity of the reservoir becomes stronger after CO₂ action.