STUDY ONTHE VARIATION RULE OF ROCK ELECTRICAL PARAMETERS FORTIGHT SANDSTONE RESERVOIRS IN CHANG 7 MEMBER OF YANCHANG FORMATION IN LONGDONG AREA OF ORDOS BASIN, CHINA

摘要

The effective stress of tight sandstone reservoirs increases due to the attenuation from the formation energy. The physical properties of reservoirs change correspondingly, which then adjusts the electrical parameters. It is difficult to comprehensively evaluate reservoirs because the electrical parameters obtained from petro-electricity experiments at normal temperatures and pressures cannot accurately reflect the reservoir properties. A total of 45 tight sand-stonc samples were measured under the effective covering pressure of 23 MPa, pore pressure of 15.6 MPa. and temperature of 60 °C. The following results arc shown.(1)Under reservoir conditions, the lithologic coefficient (a) increases, the formation cementation index (m) decreases, and the cementation index (m) is 1.05?1.21 times higher under an effective reservoir stress (30 MPa) than under normal pressures (5 MPa). 丁he cementation index (m) at 80 °C is 0.94-0.98 times higher than that at 30 °C. (2) Under reservoir conditions, the reservoir porosity has a certain stress sensitivity, and lower porosities cause more obvious stress sensitivities. The formation factor (F) increases to some extent and the saturation index decreases significantly. (3) The petroelectrical parameters are closely related to the pore structure and pore size of the rocks as well as the anti-compaction ability of rock particles.