Study On The Relationship Between Reservoirs Rocks Characteristics And Sedimentary–diagenesis Evolution Of Triassic Jialingjiang Formation In Sichuan Basin

As an important interval of oil-gas exploration in Sichuan basin and a set ofcratonic sedimentary rocks, Jialingjiang Formation developed limestones anddolomites. The natural gas reserves, accounting for7.09%of the total proven reserves,have been proved up to1141.15×10⁸m³till the end of2009. The natural gasexploration zones of Jialingjiang Formation are chiefly located in the south, east andnorth Sichuan and about85%resources here are waiting to be discovered. Supportedby the National Major Project---Study on Tectonic Evolution, Sequence StratigraphicFramework and Favorable Distribution of Permian-Triassic in Sichuan Basin; basedon multitudes of drilling, logging, core thin section as well as diverse geochemicalanalytical data, this dissertation, taking the reservoirs of Triassic JialingjiangFormation in the east, south and center Sichuan as research focus, studiessystematically the categories and characteristics of sedimentary facies of JialingjiangFormation; analyzes petrological features, types of reservoir space, physical property,diagenesis as well as the evolution of porosity under the theoretical instruction ofpetrology and geochemistry. It reveals the evolutionary characteristics of sedimentaryfacies and diagenetic phases as well as its dominant controlling factors in differentzones; summarizes the diagenetic-porosity evolutionary sequences in differentdepositional environments and sediments; comprehensively analyzes the majorcontrolling factors of reservoir development of Jialingjiang Formation and itsdistributive features; and eventually classifies the favorable exploration areasaccording to the superior superimposed correlation between sedimentation anddisgenesis.Jialingjiang Formation consists of five lithologic members corresponding tothree sequences （T1j^1T1j², T1j^3T1j⁴, T1j⁵）.Jialingjiang Formation facies can be divided into three types of facies （terrestrialfacies, transitional marine-continental facies, carbonate platform facies）, five types ofsubfacies （alluvial plain, shoreland, diamictic flat, open platform, restrictedplatform-evaporite flat） and several types of lithologic microfacies. Based on thedepositional setting types and characteristics, plane distribution of sedimentary faciesin different periods and the main controlling factors of sedimentary evolution havebeen systematically studied.The types and characteristics of reservoir rocks have also been further studied.The reservoirs chiefly include grain dolomite, mud-fine crystal powder dolostone,pinhole limestone. The III type of reservoir is developed, represented by low porosity,low permeability and strong heterogeneity. There are three types of reservoirs: pores, fracture-pore and fractures reservoirs. The last two types are commonly found incurrent exploration zone. The constructive diagenesis includes dolomitization,dissolution （gypsum dissolving, karst） and tectonic disruption. Jialingjiang Formationexperiences multiple genensis and multi-stages dolomitization. The dolomitization ofhigh porosity grainstone is related to mixed water. Dolomitization and shoal areimportant controlling factors of reservoir development of Jialingjia Formation.The relationship of pores evolution and diagenesis between different reservoirrocks has been analyzed for the first time in this paper, and corresponding poreevolution history has also been built. The pore evolutionary history of diversereservoir rocks has a close relation to diagenesis. Porosity evolution curve of ooliticlimestone, relating to fresh water dissolution, has a peak on early diagenetic stage.The evolutionary curve of grainstone limestone porosity is “M-shaped” in the2ndmember of Jialingjiang Formation, which means there are two peaks. One is related tothe syngenesis-early diagenesis dissolution and the other the epigenetic dissolution.As for crystalline dolomite, the porosity decreases to3%because of a set ofdiagenesis （such as deanhydrite, dissolution, recrystalline and compaction）. Whilecrystalline limestone is very dense due to a set of compaction, weak dolomitizationand anhydritization.The sedimentary-diagenesis phase is very complicated. In a word, shoal-moldic（ooid） pore, tidal flat-recrystalline pore-dissolution pores of gypsum, open platform–recrystalline–dissolution pores, and open platform-pleaokarst cavies are developedin south Sichuan basin. Restricted platform–dolomitization-dissolution pores ingrain-moldic, pores-intercrystalline pores, restricted platform-recrystallization-intercrystalline pores and restricted platform-intercrystalline pores-dissolutionpores of gypsum are mainly developed in Central Sichuan basin. Restricted platform-mixing water dolomitization-dissolution pores of gypsum-intercrystalline/intergranular dissolution pores and restricted platform-dissolution pores of gypsumoccurred in east Sichuan basin. The distributive characteristics ofsedimentary-diagenesis phase are clearly different in submembers of JialingjiangFormation2ndmember. Several favorable exploration blocks of the six intervals（T1j²₁～T1j1、T1j²₂、T1j²₃、T1j⁴₁～T1j³、T1j⁴₃、T1j⁵） have been determined accordingto the characteristics mentioned above.