四川盆地中部中三叠统雷三~2亚段非常规储层特征及勘探潜力

Characteristics and exploration potential of unconventional Middle Triassic Lei32reservoirs in the central Sichuan Basin

近期,CT1井在四川盆地中部(以下简称川中地区)中三叠统雷口坡组三段二亚段(以下简称雷三^(2)亚段)泥质石灰岩和灰质泥岩段获得高产油气流,可能成为四川盆地重要的油气战略接替层系。为此,基于钻井岩心、岩屑分析化验资料,开展了川中地区雷三^(2)亚段泥质石灰岩和灰质泥岩储层特征和储层主控因素研究,在通过井震结合预测了储层有利区的基础上,结合成藏地质条件分析了该区的油气勘探潜力。研究结果表明:①川中地区雷三^(2)亚段泥质石灰岩和灰质泥岩储集空间以纳米—微米级无机孔、有机孔和微裂缝为主,孔隙度介于2.00%~8.51%,平均值为2.7%,渗透率介于0.00076~1.68000 mD,平均值为0.190 mD,属于低孔、低渗非常规储层;②岩石中黏土矿物和石膏含量是影响储层孔隙度的重要因素,黏土矿物和石膏含量高的地区储层孔隙度较高,裂缝是影响渗透率的关键因素;③川中地区潟湖相储层大面积分布,发育西充—仪陇地区和WD6井—MX3井2个储层有利区,其中西充—仪陇有利区储层厚度介于30~50 m、面积约4700 km^(2);WD6井—MX3井有利区储层厚度介于10~30 m、面积约4000 km^(2)｡结论认为,川中地区雷三^(2)亚段大面积发育的潟湖相泥质石灰岩和灰质泥岩源储一体,顶底板均为膏盐岩封堵,具有原地生烃、储集、封盖等成藏特点,可以构成一种新型非常规天然气成藏系统,油气勘探潜力大,是值得探索的勘探新领域。

Well CT1 in the central Sichuan Basin recently obtained a high yield of oil and gas flows from the argillaceous limestone and limy mudstone of the second sub-member of the third member of Triassic Leikoupo Formation(Lei_(3)^(2)),making it a possible important strategic petroleum successor system in the Sichuan Basin.Based on the analysis data of drilling cores and cuttings,the characteristics of the Lei_(3)^(2) argillaceous limestone and limy mudstone reservoirs are studied,the favorable reservoir areas are predicted according to well–seismic data,and the petroleum exploration potential in the study area is analyzed with consideration to the geological conditions for hydrocarbon accumulation.The results show that the Lei_(3)^(2) argillaceous limestone and limy mudstone reservoirs have a storage space mainly composed of nano-to micron-scale inorganic pores,organic pores and micro-fractures,with a porosity of 2.00%–8.51%(2.7%on average)and a permeability of 0.00076–1.68000 mD(0.190 mD on average),indicating low-porosity and low-permeability unconventional reservoirs.The content of clay minerals and gypsum is a key factor controlling the porosity of reservoirs,and the reservoir porosity is high in areas with a high content of clay minerals and gypsum.Fractures are a key factor controlling the permeability of reservoirs.Reservoirs of lagoon facies are widely distributed in central Sichuan Basin.Two favorable reservoir areas,Xichong–Yilong and WD6–MX3,are recognized.The Xichong–Yilong area contain reservoirs with a thickness of 30–50 m and an area of 4700 km^(2).The WD6–MX3 area contains reservoirs with a thickness of 10–30 m and an area of approximately 4000 km^(2).It is concluded that the widespread argillaceous limestone and limy mudstone of lagoon facies in Lei_(3)^(2) strata serve as both source rocks and reservoir rocks,with the roof and floor sealed and capped by gypsum rocks,where hydrocarbons are generated,stored and sealed in situ,forming a new type of unconventional gas accumulation system.Therefore,the Lei_(3)^(2) reservoirs in the central Sichuan Basin have a great exploration potential and can be considered as a new target of exploration.