EXPERIMENTAL ANALYSIS ON RESERVOIR SENSITIVITY OF TIGHT SANDSTONE GAS RESERVOIRS IN LINXING-SHENFU BLOCK, CHINA

摘要

The Linxing Shenfu block is located at the eastern edge of the Ordos Basin. The Upper Paleozoic tight sandstone gas reservoirs have been the focus of exploration in recent years, and are the key gas-producing horizons. The reservoir rocks in this section are densely cemented w ith m icrodevelopment of pores and fractures. Perm eability is 0.01-53.07mD w ith average value of 0.9mD and the form ation porosity is 0.2-17.68% w ith average value of 7%, showing that it is a typical low porosity and low perm eability reservoir. Reservoir rock samples have the highest quartz content (65% -90%, average 78.8% ), followed by clay minerals (8% -22%, average 14.6%). Clay minerals have the highest illite content, follow ed by kaolinite, illite / m ontm orillonite interlayer, and chlorite. The reservoir has strong sensitivity. When the reservoir rocks are in contact w ith external fluids (drilling fluids, fracturing fluids, etc.) w hich are incom patible w ith the reservoir fluids, these fluids cause the clay minerals to hydrate and swell. The particles are broken, migrated, or precipitated to block the pore throat. As a result, the reservoir pore structure is damaged, the percolation capacity and the productivity are reduced, which causes the damage to the reservoir. Therefore, reservoir sensitivity is an im portant factor restricting o il and gas development in low-perm eability reservoirs. The sensitivity of Linxing Shenfu tight sandstone gas reservoir was analyzed through experiments. The research shows that the tight gas reservoir in the Linxing Shenfu block has medium weak velocity sensitivity w ith a critical flow rate of 0.50 m L/m in, weak water sensitivity damage and salt sensitivity damage w ith a critical salinity of 25000 ?30000 m g/L. There also exists weak to moderate weak alkali sensitivity damage in the reservoir w ith critical pH of 10-11.5. Weak to medium hydrochloric acid sensitivity damage and medium weak to medium strong mud acid sensitivity damage also exist in the reservoirs.