Study On Relationship Between Pore Structure Parameters And Electrical Properties Of Tight Sandstone

Rock physics is the basis of geophysical exploration of oil and gas reservoirs, is an important bridge between the oil and gas reservoir geological knowledge and development.Logging based in rock physics is an important means of oil and gas reservoir evaluation and production. Experimental research on rock electrical parameters of tight rock, is an important content of rock physics, is also the basis of well logging.Therefore, to carry out the research on the relationship between the electrical parameters of rocks and pore structure parameters, in-depth study of factors affecting reservoir rock electrical parameters and rules of logging response would benefit for complex reservoir interpretation and evaluation and tumbling exploration and development of oil&gas and improving the production capacity.Based on comprehensive reservoir geology research results in tight sandstone gas of Sulige field, exploratory testing method of tight sandstone electrical parameters and testing procedures is completed with the simulation in situ conditions. Relationship between the electrical parameters and pore structure and physical property parameter is modified based on electrical experiment, and the Pickett plot is drawn.The pretreatment method of rock desalting is improved; the mechanism of effects of salt on tight sandstone electrical parameters is further deepened. As the small pore throat is full of adsorbed gas, conventional cable’s extraction method is difficult to wash out soluble salt. The vacuum methanol high-pressure saturated method is selected to solve the soluble salt issue.We determined the electrical parameters of6samples, using spontaneous imbibition method and gas displacement method of water saturation, the Paleozoic Permian typical tight sandstone gas reservoir in Erdos Basin are selected as the research object. We found that rock electrical parameters are different by the two experimental methods; the saturation exponent of gas driving method is higher than that of spontaneous imbibition. The saturation exponent n is a dynamic reflection of gas/water distribution, also affected by the pore structure and physical property.Based on different distribution of water saturation and experimental results, for high permeability (K>1×10-3μm2), gas driving method is recommend; while the low permeability (K>1×10-3μm2), spontaneous imbibition is recommend. The I-Sw curve is divided into three stages according to the experimental results, the relationship between the three stages of resistivity increasing coefficient change and pore structure is also revealed. The electrical parameters of the tight sandstone are affected by the distribution of the strata water, and closely related to the fluid dynamic state.Through various effective stress rock electric experiments, we obtained that the rock electrical parameters are different under various effective stress, further deepening the response mechanism of rock electrical parameters on the effective stress based on tight sandstone stress sensitivity. Rock electrical parameters on the effective stress response was under petro physical control, the poorer rock physical properties are, the more intense rock electrical parameters response is. Under different effective stresses, the cementation exponent m, saturation index n, formation factor F have a dividing point while porosity was about5%, lithology coefficient b does not. We conclude that b does not have exact physical meaning, just to adjust the parameter fitting. In addition, electrical property changes in response to rock property changes is closely related to gas content, partially saturated samples and fully saturated sample showed an opposite trend with the effective stress increases. The calculation results show that using electrical parameters under in-situ conditions will cause errors in calculations of water saturation, the error is in the range of±16%.Based on rock electrical experiment, the relationship between pore throat radius, tortuosity and formation factor was built, and verified by mercury intrusion method. At the same time, the mechanism of the effect of pore structure parameters on the electrical parameters were studied,Compared to pore throat size, pore tortuosity has a greater impact on electrical parameters; saturated rock electrical parameters are affected more by pore structure than fully saturated rocks. Reservoir is divided into three kinds on the basis of permeability level. Among F-φ, m-φ, n-φ relationship, Ⅱ type is not so obvious. Finally, on the basis of the electrical experimental data, draw the Pickett plot.