Characteristics of Fluid-Rock Interaction in Clastic Reservoir Controlled by Evolution of Diagenetic Environment——Taking the southwest depression of Tarim basin as an example

Key words: 
• clastic reservoir /
• diagenetic environment /
• fluid -rock interaction

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.