Study On Formation Damage Mechanism Of Sandstone Reservoir Based On Micro-computed Tomography

Formation damage caused by well drilling,completion,oil testing seriously affects oil and gas production,the evaluation of which plays an important role in the process of oilfield development.And it is related to the ultimate oil and gas recovery and national economic benefits.So it is of great significance to study the mechanism of formation damage.In this study,traditional displacement experiment,CT scanning technology and finite element numerical simulation method were combined to establish a systematic formation damage evaluation method,which has a guiding significance for oilfield development.And four sets of displacement experiments were conducted using four sandstone samples.Each set was divided into three processes: first formation water injection,reverse chemical reagents injection and second formation water injection.According to the results of displacement experiments,the permeability changes of four sandstone samples were analyzed and the formation damage rates of different experimental processes were calculated respectively.In addition,we analyzed the formation damage of the four samples from the macroscopic aspect according to the changes of inlet pressure curves.We compared the pore structure changes of sandstone samples at different experiment processes by computed tomography(CT)images.the pore network models were extracted to quantitatively characterize the change of pore structure parameters(pore radius,throat radius,coordination number and tortuosity).Finally,a 2D microscopic seepage channel model was designed according to the real core structure.The flow rule of solid particles in fluid was simulated by finite element method.And six sets of numerical simulation studies were carried out by changing the wetting angle,and the displacement effect,pressure distribution and maximum velocity distribution under the same wetting angle were analyzed.According to the results,it was found that the injection of chemical reagents increased the inlet pressure and led to the decrease of core permeabilities.The particle migration phenomenon was found through the quantitative analysis of CT images.The "sensitive regions" of four sandstone cores were found by the pore network models.And it was found that after the injection of chemical reagents,the average pore radius,the average throat radius and the average coordination number of the cores decreased,but the average tortuosity increased through the microscopic pore-throat data.In addition,it was found that there was a positive correlation between the pressure and the export rate of solid particles during the numerical simulation of particle migration.However there was a negative correlation between the export rate of particle migration and matrix deformation degree.Finally,it was found that the effect of hydrophilic reservoir was the best in the process of water flooding during the numerical simulation of wettability alteration.When the wettability of the reservoir was neutral,the maximum velocity of the fluid in the cores was the highest,the pressure distribution was uniform,and the pressure was the lowest compared to the oil-wetting and water-wetting conditions.