四川盆地深层-超深层天然气勘探进展与展望

Deep and ultra-deep natural gas exploration in the Sichuan Basin:Progress and prospect

四川盆地深层-超深层天然气勘探近年来虽然取得了重大突破,但天然气整体探明率仍然较低。为了进一步明确四川盆地深层-超深层天然气的勘探前景,对先期在常规天然气领域发现的普光、元坝、安岳、龙岗等大型礁滩气田(藏)与该盆地南部丁山、东溪深层非常规天然气--页岩气勘探突破进行了系统深入地研究与分析。研究结果表明:①对于常规天然气领域的深层-超深层礁滩气藏来讲,大型高能相带是控制规模性礁滩储层发育的基础,储层原始孔隙度高,早成岩期大气淡水溶蚀、白云岩化、不整合岩溶、"孔缝耦合"则主要控制次生孔隙的发育,热液流体对储层的贡献具有双面性,烃类早期充注等保持性成岩作用则使得早期孔隙得以保存至今,大型天然气成藏多具有"近源富集、相态转化、动态调整"的特点,持续保存是关键;②对于非常规天然气领域的深层-超深层页岩气藏来讲,页岩气普遍具有"高地层压力、高孔隙度、高含气量"的"超压富气"特征,"石英抗压保孔"和"储层流体超压"是深层优质页岩高孔隙度发育的关键,晚期构造作用较弱是深层页岩气持续保持"高地层压力、高含气量"的主要原因。结论认为,四川盆地深层-超深层常规与非常规天然气勘探潜力巨大;深层-超深层天然气地质目标识别与"甜点"预测以及高温高压工程工艺等核心技术的进步,是深层-超深层天然气高效勘探的前提和保障。

In recent years,major breakthroughs have been made in natural gas exploration in deep and ultra-deep strata in the Sichuan Basin,but the overall successful rate is low.To further clarify the prospects there,it is necessary to make an in-depth analysis of the previously discovered large-scale reef-shoal gas fields such as Puguang,Yuanba,Anyue and Longgang and deep shale gas discovery in Dingshan and Dongxi,southern Sichuan Basin.On one hand,large high-energy facies are the basis for controlling the development of large-scale reef-shoal reservoirs in conventional reef-shoal areas.The reservoir original porosity is high.The atmospheric freshwater dissolution in the early diagenetic stage,dolomitization,unconformity karst,and"pore-fracture coupling"mainly control the development of secondary pores.The contribution of hydrothermal fluids to reservoir is double-sided,and such early pores can be preserved till present due to those retention processes such as early hydrocarbon charging.Apart from continuous preservation as the key factor,most gas reservoirs are featured by"near-source enrichment,phase transformation,and dynamic adjustment".On the other hand,deep shale gas generally has the characteristics of"high pressure,high porosity,and high gas content",that is,"overpressure and rich gas".The key to the development of high-quality deep shales with high pores are"quartz compression retaining hole"and"reservoir fluid overpressure".The weak tectonic effect in the late stage is the main reason for deep shale gas to maintain the"high pressure and high gas content".In conclusion,technological advances like geological target identification and"sweet spot"prediction,as well as deep,high-temperature and high-pressure engineering processes,are the guarantee for efficient exploration of conventional and unconventional deep and ultra-deep natural gas,which has great potential in the Sichuan Basin.