川西新场气田沙二段致密砂岩储层岩石力学性质

LITHOMECHANICAL PROPERTY OF TIGHT SAND RESERVOIRS IN THE SECOND MEMBER OF SHAXIMIAO FORMATION IN XINCHANG GAS FIELD,WEST SICHUAN BASIN

对川西新场地区侏罗系沙溪庙组二段致密储层样品所进行的岩石力学实验结果表明,岩石抗张及抗压强度随着岩石密度的增加而增大、岩石孔隙度的增加而减小,且随着岩石粒度的增加,抗张强度减小、抗压强度增大;砂岩的弹性模量明显高于泥岩,且随着岩石密度的增加而增加、孔隙度的增加而减小。与常温常压下相比,模拟地层条件下沙溪庙组泥岩饱和介质为气体时,抗压强度高3.2倍,弹性模量低2.35倍,泊松比高2倍;当砂岩饱和介质为水时,与饱和气体介质的砂岩相比,强度及弹性模量均降低,泊松比增大。这说明水介质对岩石有"软化效应"。进而在实验研究的基础上,应用测井、压裂资料计算了地层的岩石力学参数,通过对三种方法所得结果的对比分析,评价了地层条件下岩石力学参数,由此获得了较为合理、可信的地层岩石力学参数剖面。

Lithomechanical experiments are performed on samples of the tight sand reservoirs in the second member of Jurassic Shaximiao Formation in Xinchang gas field, West Sichuan Basin. The experiment results show that rock tensile strength and compressive resistance increase with increasing rock density, but decrease with increasing rock porosity. The tensile strength decreases but compressive resistance increases along with the increase of grain size. The elastic modulus of sandstone is evidently higher than that of mudstone, and increases along with increasing rock density but decreases along with increasing porosity. Under the simulated formation conditions, the gas-saturated mudstone of Shaximiao Formation has a 3.2 times larger compressive resistance, a 2.35 times lower elastic modulus and a 2 times higher poisson's ratio than those under normal temperature and pressure. In comparison with gas-saturated sandstone, the water-saturated sandstone has lower compressive resistance and elastic modulus but larger poisson's ratio, indicating water has a softening effect on rocks. Based on experimental study, logging and fracturing data are used to calculate the lithomechanical parameters. A comparative analysis is performed on the results obtained with these 3 methods to evaluate lithomechanical parameters under formation conditions. Rational and reliable profiles of lithomechanical parameters are obtained.