盐津-珙县地区五峰组-龙马溪组页岩气富集成藏条件

Accumulation condition for Wufeng-Longmaxi Formation shale gas of Yanjin-Gongxian area

利用野外观察及实验数据资料,对盐津-珙县地区五峰组-龙马溪组页岩气形成条件进行分析,并探讨其富集成藏的主控因素.研究结果表明盐津-珙县地区五峰组-龙马溪组下部黑色页岩是深水陆棚沉积产物,该区页岩气'甜点段'五峰组—段—四段和龙马溪组一段—五段发育完整,有机碳质量分数在2.7%~6.0%之间,主要为中高-高有机碳含量,富有机质黑色页岩厚度分布在30~50 m.在高含气层位,纳米级有机质孔和黄铁矿晶间孔大量发育,平均孔隙度为2.28%~3.48%,为吸附气和游离气提供良好的储集空间.研究区内构造强度较弱,通天断层少,具有良好的顶底板条件,压力系数平均大于1.0,因而保存条件良好.分析表明,高有机碳含量、纳米级孔隙发育、高脆性矿物含量、高压力系数是盐津-珙县地区页岩气富集成藏的主控因素.

The formation conditions of shale gas in Wufeng-Longmaxi Formation of Yanjin-Gongxian area were analyzed on the basis of field observation and experimental data,and then the main factors for shale gas accumulation were discussed. Results show that black shale at the bottom of Wufeng-Longmaxi Formation is a deep-water shelf deposit product. The dessert shale gas from the first stage of Wufeng to the fourth stage of Longmaxi was complete. The organic carbon content is between 2. 7%- 6. 0%. Mainly for the high organic carbon content,the thickness of black shale rich in organic matter is 30-50 m. In the high gas horizon,nanometer organic pores and pyrite intracrystalline pores are abundant,and the average rate of porosity is 2. 28%- 3. 48%,providing a good reservoir space for the adsorbed gas and free gas. Structural strength in the research area is weak and large faults are less. There are good conditions of roof and floor. The pressure coefficient is more than 1,which reflects the suitable preservation condition. The main factors for shale gas accumulation are as follows: deep shelf sedimentary environment,high organic carbon content,abundant nanometer pores,high level porosity,and high pressure coefficient.