Rock mechanics characteristics of tight sandstone reservoirs in the Yanchang Formation of the southern block in Ordos Basin

Abstract The limited porosity and permeability are the key factors hindering the exploitation of tight sandstone reservoirs. The petrological characteristics, as well as the physical properties of tight sandstone reservoirs were experimentally analyzed. Meanwhile, the mechanical properties were also investigated, and the dynamic and static values were gained. The acoustic velocity and mechanical parameters of rocks obtained from the experiments were fitted to data, and the dynamic-static conversion relationship between two elasticity parameters was developed. The results showed that the sandstone fillings in the Chang 7 reservoir range from approximately 0.22% to 24.13%, mainly composed of cement. The porosity decreases significantly with the filling material content, showing a negative correlation between the two. The reservoir porosity differs from 4% to 13%, with the main values falling between 6% and 8%. The reservoir permeability is between 0.01 and 5.00 mD, with the main values falling between 0.1 and 0.5 mD. The elasticity parameters derived from experiments are compared with those derived from well logging. The dynamic Young’s modulus is 45-75 GPa, and the static value ranges from 15 to 60 GPa. The overall correlation coefficient between the two is 0.831, the distribution range of dynamic Poisson’s ratio is 0.2-0.4, while the static value range is 0.2-0.5. There is a weak correlation between dynamic and static values, largely due to the influence of factors such as stress, rock, and other forms of heterogeneity.