Shunan Area The Changyuan Dam Constructed With Jialing Sedimentary Facies And Favorable Reservoir Facies Prediction

The Jialingjiang Formation of Lower Triassic at Changyuanba structure belt in the Southern Sichuan area is carbonate interlayered with gypsum rock in environments of open-platformsâ†'localized mesaâ†'evaporation-mesa. The grain and pinhole limestone, grain and pinhole dolomite in some region are about ten to several ten meters in thickness and are favorable reservoir strata.This study is aimed to better understand the effects of sedimentation and diagenesis process to reservoir strata and furthermore vertical and lateral distribution patterns of reservoir through comprehensive studies of sediment microfacies, diagenesis and reservoir properties of Jialingjiang Formation in Changyuanba structure belt, consequently evaluate the gas reservoir specially for members from T₁j²₁ to T₁j¹, T₁j² and T₁j⁴₁ to T₁j³.The relationship of reservoir formation, evolution and distribution pattern in connection to sedimentary facies, diagenetic facies and structural evolution for Jialingjiang Formation in Chagyuanba has been systematically studied by analysing the characteristics of sedimentary petrology and reservoir diagenesis process and applying theories of sedimentology, reservoir geology and tectonics. It has been recognized that the open platform, localized platform and evaporite mesa were developed in Jialingjiang Formation of early Triassic in this region. There are three main cycles shoaling upward, the first cycle from T₁j¹ to T₁j² , the second from T₁j³ to T₁j⁴ and the third from T₁j⁵₁ to T₁j⁵₂ (hemicycle) .The first and second cycles are complete cycle from open platform faciesâ†'localized platform phaseâ†'evaporite mesa phase, and the third cycle is an incomplete cycle from localized platform phaseâ†'evaporite mesa phase. Reservoir spaces are mainly remaining of intergranular hole, induced porosity and cracks, or in more detail, remaining intergranular hole of the oolitic dolomite, intergranular enlarged solution hole, gypsum dissoved hole of gypseous dolomite, inter-crystalline hole of dolomite and tectonic fissures. The cracks are the main migrtion routes, and secondly the inter-crystalline slits and remaining intergranular slots. Reservoirs can be divided into several zones vertically in this region. The grain bottomland of upper T₁j¹ to T₁j²₁ has better remaining intergranular hole and enlarged solution hole in contrast of the grain dolomite, and could be favorable reservoir. Reservoirs in T₁j²₂ to T₁j²₃ and T₁j³ to T₁j⁴ are mainly the dolomitic plateau and lake clay and crystal powder dolomite microfacies, inter-crystalline hole (inter-crystalline micropore) and slit, and some of the grain dolomite could be favorable reservoir. The most favorable reservoirs in favorable facies zones of Jialingjiang Formation in this area are oolitic dolomite of shoal microfacies and dolomite with gypsum solution hole of gypseous dololitic plateau and dololitic gypseous plateau, and secondly dolomites with inter-crystalline micropores.