外源补给型页岩气的发现及油气地质意义

Discovery of exogenous type shale gas and its geological significance to hydrocarbon exploration

野外调查发现,四川盆地及周缘五峰组内发育一套稳定的滑脱层,不仅厚度稳定(0.3~1.5 m),而且产出层位特殊,可能为五峰组—龙马溪组页岩气主产层底部的一套高渗输导层。根据滑脱层对页岩气富集控制作用的差异,可将页岩气分为外源补给型和原位富集型,华地1井和新地2井页岩气的重大发现,初步证实了该划分方案的可操作性。钻探也证实,华地1井投资回本周期与现今页岩气探井投资回本周期相近,滑脱层产生的'面'连通油气输导能力可能高于现今页岩气水平井人工压裂产生的'线'连通油气输导能力。外源补给型页岩气富集规律不仅能解释现今页岩气勘探开发过程中发现的诸多理论问题,而且对其进行深入研究将有助于中国页岩气富集规律和复杂构造区内油气动态成藏机理研究。配套羽状水平井技术将攻克因页岩气水平井压裂导致成本高、环境污染严重的行业技术瓶颈,实现页岩气免压裂商业开发。

According to field survey,it is found that a set of stable detachment layer is developed in Wufeng Formation of Sichuan Basin and its periphery,characterized by stable thickness(0.3-1.5 m)and special occurrence horizons,and may be a set of high-permeability carrier bed at the bottom of chief shale gas horizons in WuFeng-Longmaxi Formation.Based on the differences in the control of detachment layer on the enrichment of shale gas,shale gas can be divided in exogenous-supply type and in-situ enrichment type.Therefore,the operability of this classification scheme is preliminarily validated by agreat discovery of shale gas in Well HD1 and Well XD2.Meanwhile,it is also confirmed through exploratory drilling that the investment return cycle of Well HD1 is similar to that of the current shale-gas exploratory well,and the hydrocarbon transport ability of"connecting planes"caused by detachment layer is greater than that of"connecting lines"generated by the artificial fracturing of shale-gas horizontal well.The enrichment laws of exogenous-supply shale gas not only well explain various problems in the present shale gas exploration and development processes,but also provide assistance in studying the enrichment laws of shale gas in China and the dynamic hydrocarbon accumulation mechanisms in complicated structural zones.The matched pinnate horizontal well technology is able to break through the industrial technical bottleneck of high cost and severe environmental pollution caused by shale-gas horizontal well fracturing,so as to realize the commercial fracturing-free development of shale gas.