四川盆地南部地区寒武系油气勘探前景

Oil and Gas Exploration Prospects of Cambrian in Southern Sichuan Basin

为明确四川盆地南部地区寒武系常规油气和页岩气的勘探前景,应用岩相学和地球化学分析手段相结合,对研究区中上寒武统娄山组和下寒武统清虚洞组的厚度、孔隙度、渗透率、孔隙类型和下寒武统筇竹寺组的厚度、总有机碳质量分数w(TOC)、镜质体反射率Ro、矿物组分等进行了深入剖析。结果表明:①川南地区烃源岩厚度大(80～100m),w(TOC)高(3%～5%),为一套中-好的过成熟后期阶段烃源岩(Ro为3.0%～4.8%),矿物组分与美国重要页岩气产层Barnett页岩相似,其中石英、长石和黄铁矿的体积分数为31%～50%,黏土矿物体积分数为29%～53%;②威远地区下寒武统九老洞组黑色页岩含气量达0.43～0.86m3/t;微孔隙发育,主要为粒间孔,孔隙直径达5～10μm,裂缝密度一般为30～50条/m;③中上寒武统娄山组和下寒武统清虚洞组总体上是寒武系最重要的常规储层,储层内部沥青质量分数一般为3%～6%,储集空间主要为粒间溶孔-晶间孔等,平均孔隙度为1.85%,平均渗透率为2.25×10-3μm2;④在川东南地区靠近盆地边缘的斜坡带,寒武系具有较好的常规油气藏勘探前景,而川东南缘和川西南地区筇竹寺组下部具有较大的页岩气勘探潜力。

In order to identify the exploration prospect of Cambrian conventional oil and gas and shale gas in southern Sichuan Basin,this paper,combining the petrographic and geochemical methods,makes a thorugh analysis of the thickness,porosity,permeability,porosity type of Middle-Upper Cambrian Loushanguan Formation and Lower Cambrian Qingxudong Formation,as well as the thickness,TOC,Ro,mineral composition of Lower Cambrian Qiongzhusi Formation.The results show that：（1） The hydrocarbon source rocks in southern Sichuan Basin are thick（80-100 m）and of high organic matter content（3%-5%）.It is a set of general-good late-mature stage of hydrocarbon source rocks（Ro is about 3.0%—4.8%）,and its rock components are similar to Barnett Shale which is the important layer of gas production in the United States.The content of quartz,feldspar and pyrite is 31%-50% and clay mineral content is 29% to 53%;（2） The capacity of black shale gas of Lower Cambrian Jiulaodong Formation in Weiyuan is about 0.43 m3/t-0.86 m3/t and the micro-porosity is highly developed and its mainly type is intergranular pore with pore diameter of 5-10 μm and fracture frequency from 30 to 50 per meter;（3） Middle-Upper Cambrian Loushanguan Formation and Lower Cambrian Qingxudong Formation are the most important conventional reservoirs.Within the reservoir,bitumen content is generally 3%-6% and the storage space is mainly the intergranular dissolution hole and intercrystalline pores.Average porosity is 1.85% and average permeability is 2.25×10-3 μm2.There is a good exploration prospect for Cambrian conventional oil and gas in southeastern Sichuan Basin,while the lower part of Qiongzhusi Formation has considerable potential for shale gas exploration in the southeastern edge and the southwest of Sichuan Basin.