川西新场地区须五段泥页岩超压成因及其对含气性的影响

Genesis of Overpressure and Its Effect on Gas Content in the Fifth Member of Xujiahe Formation in Xinchang Area,Western Sichuan Basin

页岩气储集层中往往发育异常高的地层压力,其压力的大小不仅直接影响了泥页岩中有机质的热演化生烃作用,而且还决定着页岩气的保存和富集程度。为了研究川西新场地区须五段泥页岩的异常高压成因及其对含气性的影响,选取该地区3口井的页岩岩心样品进行现场解吸、X衍射矿物分析和等温吸附等一系列分析测试来辅助说明超压产生的原因。然后结合前人研究成果和测试数据,对泥页岩的异常高压成因进行了定性分析,初步探讨了泥页岩异常高压发育与含气量之间的关系。分析表明:造成川西新场地区须五段泥页岩异常高压现象的原因主要有欠压实作用、生烃作用、粘土矿物脱水作用和构造挤压作用。页岩含气量与异常高压的发育程度呈正相关关系,页岩异常高压越发育,其含气量越大,产气量也越高。同时压力系数可以作为保存条件的综合判别指标,川西新场地区须五段泥页岩压力系数较高,保存条件较好。

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 or-der 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 adsorp-tion experiment.Based on the experimental data,we performed a qualitative analysis on the formation mecha-nism of abnormal high-pressure combining with previous research results.Through data analysis,the relation-ship 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-pres-sure 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 coef-ficient 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.