Sensitivity Evaluation and Stimulation Optimization of Ultralow Permeability Sandstone Reservoir

Acidizing operation is normally applied in low permeability reservoirs, but if the acid system is not utilized properly, it will cause sensitive damage to the reservoir. As for the Sanjianfang Formation of the sandstone reservoir in the Shanshan oilfield, the problems existing in acidizing are especially serious. For these problems, the basic characteristics, sensitivity characteristics, and damage mechanisms were obtained by means of X-ray diffraction (XRD) analysis and scanning electron microscopy. Meanwhile, gas porosity and permeability were measured, and reservoir sensitivity characteristics were evaluated. The results showed that the reservoir rocks are mainly feldspar lithic sandstone and the clay minerals are mainly kaolinite and montmorillonite, which belong to the high clay mineral reservoir. It is an unsaturated reservoir with normal formation pressure that has low porosity and ultra-low permeability, heavy crude oil, and low porosity. The reservoir is highly stress sensitive, moderately weak velocity sensitive, alkali sensitive, water sensitive, salt sensitive, and weak acid sensitive. Based on these results, a multinanoscale stimulating liquid system was developed in the laboratory, and field application of this fluid system combined with mud acid was carried out. The combination system of multinanoscale highly efficient stimulation fluid and mud acid can meet the optimal dissolution rate of rock during the acidizing process and can increase the permeability of the targeted reservoir by 2.68 times, with a remarkable field application effect. The research results can provide a scientific basis for acidizing and stimulation of ultralow permeability sandstone reservoir.