摘要:
塔西南坳陷不同时代碎屑储集岩成岩环境经历了由酸性向碱性演变的过程,成岩环境地球化学性质的这种转变直接控制了发生在碎屑岩成岩体系中的流体—岩石相互作用特征。酸性成岩环境形成于烃源岩—储集岩系统中有机—无机反应最活跃时期,主要分布在早成岩阶段A、B期和晚成岩阶段A期,当古地温小于90℃,Ro值在<0.5%～1.3%之间,酸性的孔隙介质与骨架颗粒之间主要发生蚀变、溶解和氧化硅沉淀作用。当古地温达到90℃以上,Ro值在1.3%～>2%时,有机质脱羧基停止,有机酸发生分解,CO2来源减小,使孔隙流体性质由酸性向碱性变化,成岩环境呈碱性,这时晚期含铁碳酸盐矿物交代作用最为活跃,同时伴随自生伊利石和绿泥石沉淀、陆源伊利石重结晶成绢云母、高岭石向伊利石或绿泥石转变等作用。成岩环境在其演化过程中,由于孔隙流体性质的转变,破坏了早期成岩环境的物理化学平衡状态,使旧的成岩反应停止,新的成岩反应开始,从而形成多种矿物蚀变→交代→溶解→沉淀过程,导致碎屑储集岩结构和孔隙组合特征上的差异,流体-岩石相互作用的强度和范围决定了碎屑储集岩的储集性能及分布特征。
Abstract:
The diagenetic environment of clastic reservoirs of different period in the southwest depression of Tarim basin have undergone a change from acidic to alkalic one. Such a change of geochemistry nature of diagenetic environments has directly controlled the characteristics of fluid-rock interaction in clastic system.The acidic environment formed during the most active period of organic-inorganic reaction in source-reservior rock system, which mainly distributed in A and B period of early diagenetic stage and A period of late diagenetic stage with geotemperature less than 90℃ and R o value ranging from 0.5% to 1.3%, and acidic pore fluid could dissolve and alter the framework grains and precipitate SiO2. When the geotemperature reached over 90℃ and R o ranging from 1.3% to 2%,organic acid began to decompose, and dehydroxyl-base ceased, the source of CO2 decreased and resulted in the nature of pore fluid changing from acidic to alkalic to form the alkalic environment. During this period, the late Fe-bearing carbonate replacement was the most active reaction, simultaneously resulting in the precipitation of authigenic illite and chlorite, recrystallisation of terrigenous illite and kaolinite changing to illite and chlorite,etc.. During the evolution of diagenetic environment, the change of pore fluid destroyed the physicochemistry equilibrium of diagenetic environment leading to the end of the old diagenetic reactions and beginning of new diagenetic reactions and forming lots of alteration-replacement-dissolution-precipitation processes which could produce the differences of reservoir rock texture and pore assemblage features.
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