四川盆地震旦系气藏TSR证据及控制因素

Evidence and controlling factors of thermochemical sulfate reduction in the Sinian gas reservoirs,Sichuan Basin

综合分析四川盆地高石梯—磨溪(高—磨)地区震旦系天然气、储层沥青、流体包裹体组分、硫化物分布及硫同位素特征等,认为高—磨地区震旦系曾发生过硫酸盐热化学还原反应(TSR),但TSR强度整体较弱,且主要受走滑断裂相关的热液流体活动控制。主要证据如下:①高—磨地区及四川盆地周缘震旦系储层中多处发育方铅矿、闪锌矿、黄铁矿、重晶石等硫化物及硫酸盐矿物,硫同位素富重硫特征明显,δ^(34)S值普遍大于12‰,反映研究区内硫化物硫源为海水中硫酸盐,且与TSR有关;②高—磨地区震旦系储层固体沥青S/C值范围为0.031~0.059,具有TSR沥青典型特征;③部分流体包裹体中H_(2)S含量较高,含单体硫、沥青、方解石子晶的流体包裹体是发生TSR的直接证据;④震旦系气藏中H_(2)S含量为0.24%~6.8%,平均值为1.22%,为微—高硫化氢气藏,地层中缺乏膏盐岩沉积,且地层水中未见SO_(4)^(2-),与全球发生TSR的高含硫气藏截然不同,说明川中震旦系TSR强度整体较弱;⑤高—磨地区震旦系发现硫化物的井位主要分布在北西、北西西向走滑断裂附近,分布受断裂控制明显,TSR的硫源可能为断层沟通的深部热液流体,TSR主要发育于断层附近,为断控型TSR。四川盆地震旦系储层中烃类发生TSR,产生的H_(2)S促使了铅锌矿等硫化物矿床的形成,即烃类的聚集、裂解与热液流体活动、TSR及MVT型铅锌矿的形成是紧密相连的,是开展深层有机—无机相互作用研究的理想地区。

Comprehensive analysis of reservoir bitumen,fluid inclusion composition,sulfur distribution and sulfur isotope characteristics in Sinian system,Gaoshiti-Moxi area of Sichuan Basin,shows that thermochemical sulfate reduction(TSR)occurred in the Gaoshiti-Moxi area,but the TSR is weak and it is mainly controlled by hydrothermal fluid flow related to strike-slip faults.Main evidences are as follows:(1)Sulfide and sulfate minerals such as galena,sphalerite,pyrite and barite are developed in many Sinian reservoirs in outcrops of the peripheral area of Sichuan Basin and Gaoshiti-Moxi area.The sulfur isotope is characterized by high δ^(34)S values,which are generally greater than 12‰,indicating that the source of sulfur is seawater and related to TSR.(2)The S/C range of Sinian solid bitumen in Gaoshiti-Moxi area is 0.031-0.059,which has typical characteristics of TSR bitumen.(3)The content of H_(2)S in some fluid inclusions is high,and the fluid inclusions containing elemental sulfur,bitumen and calcite daughter crystals are direct evidence of TSR.(4)The content of H;S in Sinian gas reservoir is 0.24%-6.8%,with an average of 1.22%.It is a micro-high H_(2)S gas reservoir.The absence of gypsum deposits in the formation and SO_(4)^(2-) in the formation water is quite low,which is completely different from the global high sulfur gas reservoir where TSR occurs,indicating that the effect intensity of TSR in Sinian gas reservoir is weak.(5)Wells,which have found sulfide in the Sinian system in Gaoshiti-Moxi area,are mainly located near the NW and NWW strike-slip faults,and the distribution is obviously controlled by faults.TSR may be derived from deep hydrothermal fluids communicated by faults,and TSR is mainly developed near faults,which is fault-controlled TSR.H_(2)S generated by TSR of hydrocarbons in Sinian reservoirs in Sichuan Basin promotes the formation of lead-zinc deposits and other sulfide deposits,that is,hydrocarbon accumulation,cracking and fracture fluid activity,TSR and the formation of MVT type lead-zinc deposits are closely linked,which is an ideal area for the study of deep organic-inorganic interaction.