Digital Core Reconstruction And Seepage Simulation Of Tight Sandstone

At present,the focus of oil and gas exploitation in China is transferring to unconventional oil and gas,but it is difficult to exploit because of the complex reservoir environment.In order to improve the mining efficiency of unconventional energy,it is necessary to test the conventional parameters of the reservoir and study the development plan,and it requires a variety of experiments on the rock samples of the reservoir and a detailed understanding of the internal structure of the reservoir.However,the common methods have great disadvantages and can hardly repeat the experiments.Now,the rise of digital core technology based on CT scan solves this problem very well.By scanning core to establish a model,we can obtain more accurate internal structure of rock to explain the physical differences of rock.In this paper,the current situations of core research at home and abroad are fully understood and summarized.Five cores of tight sandstone reservoir in Changqing Oilfield are studied by using the method of establishing digital core with CT scan.After a series of operations,such as core scanning,image denoising and filtering,selection of cutting range,image segmentation and extraction of pore throat network,and construction of ball model,the parameters of every pore throat are obtained;and the seepage simulation of the 3D digital core is carried out to obtain the absolute permeability,pressure distribution and simulation streamline.The conclusion is as follows:1.In order to retain the edge information of the image,the median filter is better than the Gauss filter for the dense sandstone;in order to make the cutting core more representative,the porosity change rules of different cutting size cores are repeatedly compared,and it is found that the cutting size side length element of 600 × 600 × 600 can represent the properties of five cores best;2.Different image segmentation methods are used to process the threedimensional core,and we can get the conclusion that threshold segmentation has the best application effect for complex and dense sandstone.In this paper,by establishing the corresponding relationship between threshold and average face rate,the average face rate is close to the measured porosity,and the selection of the threshold range of pore throat is the most appropriate;3.We transform the extracted pore throat network structure into a ball and stick model by using the maximum sphere method,and analyze the pore throat parameters.The results are as follows: 1)for tight sandstone,multiple different parameters lead to the phenomenon of "similar porosity,but large difference in permeability";2)within a certain number of pore throats and a certain radius of pore throats,the influence of pore throat radius on permeability is far greater than that of pore throats 3)no matter from coordination number or pore throat radius,there are a lot of isolated pore clusters in tight sandstone,i.e.useless pores,which is the reason for the low permeability of tight sandstone;4.By comparing the pressure distribution diagram with the simulated flow diagram obtained by seepage simulation,according to the distribution of pressure area and the connectivity and velocity of streamline,we can infer the relationship between the permeability of each core,and draw the conclusion that the permeability is determined by the dominant channel of the core.