摘要
川东南丁山地区是四川盆地页岩气主要勘探开发区，尽管已有多口井获得高产页岩气试气产量，但由于递减速率快和估算的最终可采储量()低，导致该区尚未获得商业开发。为了明确复杂构造区页岩气成藏富集特征，预测有利目标区，通过岩心观察、笔石带识别与对比以及扫描电镜观察等手段，对川东南丁山地区五峰组-龙马溪组页岩岩石类型、展布特征、储集类型和含气量等进行了分析。研究结果表明：川东南丁山地区五峰组-龙马溪组页岩岩石类型主要包括硅质页岩、含灰-灰质页岩、粘土质页岩和粉砂质页岩4种，其中优质页岩为WF2-LM4笔石带的硅质页岩，厚度介于6~10 m。储集空间主要包括有机质孔、矿物质孔和微裂缝，靠近盆地边缘无沥青充填的溶蚀孔相对发育，反映了较差的页岩气保存条件。与涪陵页岩气田的对比分析表明，丁山地区五峰组-龙马溪组WF2-LM4笔石带硅质页岩厚度较薄，在靠近盆缘断裂带的地区埋藏较浅，页岩气藏压力系数低，为浅层常压页岩气藏；向盆内方向压力系数增加，埋深较大，属于深层超压页岩气藏。建议在川东南地区WF2-LM4笔石带硅质页岩厚度大、埋藏适中和保存条件较好的地区开展页岩气的勘探工作。
Abstract
The Dingshan area in southeastern Sichuan Basin is one of the focal points for shale gas exploration and development in China.Despite some promising test results achieved from several wells drilled in the area, the subsequent rapid production decline rate and low EUR estimations make their development uneconomical.To tackle the problem, efforts were exerted to the characterization of shale gas accumulations and predication of potential exploration targets in such areas.The representative Wufeng-Longmaxi Formation shale in the Dingshan area was chosen to conduct analyses of the shale rock types, distribution characteristics, reservoir types and gas content by means of core observation, identification and correlation of graptolite belts and scanning electron microscope (SEM) observation.The results show that there are four types of shale: siliceous shale, lime-calcareous shale, clayey shale and silty shale.Among them, the siliceous shale in the graptolite belt of the second member of the Wufeng Formation and the fourth member of the Longmaxi Formation (WF2-LM4) is potentially high-quality shale rocks with a thickness of 6 m to 10 m.The reservoir space is mainly organic-matter pores, mineral pores and micro-fractures.The dissolution pores that are well developed near the margin of the basin are found to be no signs of asphalt, indicating a poor preservation condition for shale gas.Compared with the Fuling shale gas field, the siliceous shale rocks in the graptolite belts in the Dingshan area are thinner, with those buried shallow in the faulting zone near the edge of the basin containing shallow normal-pressure gas reservoirs of low formation pressure coefficients, and those distributed basinward having deep, over-pressure gas reservoirs of high pressure coefficient.It is suggested that the exploration of shale gas should be focused on parts with large thickness, moderate burial depth and good preservation conditions in the WF2-LM4 zones of southeastern Sichuan Basin.
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