Study On The Diageneses Of The Clastic Reservoirs From The Jurassic Shaximiao Formation In The Western Sichuan Area

Shaximia Formation is one of the most important gas reservoirs in the weastern Sichuan Area. Based on the logging data, outcrop observation, indoor analyses and measurement of rocks,the diagenesis characters of Jurassic Shaximiao Formation were studied in detail in the weastern Sichuan Area, by the sedimentological, petrological theories and methods. The main types of diagenesis and effects on the reservoir were discussed. Furthemore, an evolvement model of reservoir diagenesis was setup.In lithology, the reservoir rocks in research area were dominated by feldspathic litharenite and lithic greywacke with lower textural maturity and compositional maturity. The pore types seen in the reservoir included primary pore, intergranular pore, intercrystal pore, intraparticle and interparticle dissolution pore, intercrystal soluted fissures, etc.By way of thin section, casting sheet analysis and SEM,EDX analysis, such studies were carried as rock types, diagenesis facies, diagenetic stage, pore types, the diagenesis of the reservoir and its influence on the pore texture. The diageneses of reservoir sandstones were mainly underwent comprise compaction, pressolution, cemeniation, metasomatism, and dissolution, among which compaction and cementation reduced porosity, dissolution is benefieial to improvement of the reservior.The result shows that chlorite rims grew vertically on the grain surface. But automorphic crystal are different at various times, the fist generation chlorite have poor automorphic crystal, as honeycomb chlorite, rich in SiO2 and poor in Fe. The second generation chlorites have well automorphic crystal, as rosette chlorite, rich in Fe and poor in SiO2. During diagenetic stage, the fist generation chlorite preserved the primary porosity, and the second generation chlorite solution some quartz coment. "Water consumption"of mineral transfer to chlorite can lead formation water and pressure decrease. Pressure differences between relevant formation and wall rock make hydrocarbons emplace easily to form the effective reservoir.