Abstract:

There is always abnormal high-pressure in shale reservoirs. It has not only an effect on organic matter maturation and hydrocarbon generation, but also determines the preservation and enrichment of shale gas. In order to study formation mechanisms of abnormal highpressure and its effect on gas content in the fifth member of Xujiahe Formation of Xinchang area in western Sichuan Basin, shale cores from three wells are selected to be analyzed by various methods such as field desorption, X-ray diffraction mineral analysis and isothermal adsorption experiment. Based on the experimental data, we performed a qualitative analysis on the formation mechanism of abnormal high-pressure combining with previous research results. Through data analysis, the relationship between abnormal high-pressure development in shale and gas content is figured out. The study shows that the formation mechanism of the fifth member of Xujiahe Formation in the study area is summarized as follows: undercompaction, hydrocarbon generation, clay mineral dewatering and structural compression. The high-pressure development in shales also shows a positive correlation with total gas content, the better the highpressure development is, the greater the gas content is, and therefore the higher the gas production is. The pressure coefficient can be regarded as a comprehensive discrimination criterion for preservation condition, and the results show that the pressure coefficient is relatively high and the preservation condition is relatively good in the fifth member of Xujiahe Formation in Xinchang area, western Sichuan Basin.

Key words: western Sichuan Basin, the fifth member of Xujiahe Formation, abnormal high-pressure, formation mechanism, gas content