The Sedimentary Facies And Favourable Area Forecast Of The Marine Shale Formations In Xiangzhong Area

Xiangzhong basin is neopaleozoic sedimentation basion area that is developed inbasement of shallow metamorphic rock in the lower Paleozoic.There develops marine shaleformations with a high abundance of the of organic matter which reaches basic reservoirgeological conditions of forming the shale gas.This paper makes use of shale stratigraphiclithology、thickness、organic matter abundance、organic type and maturity, etc, which areobtained by the exiting wells.Firstly, the sedimentary facies and sedimentary background ofmain shale formations is studied; and then the organic geochemistry features in this area arestudied and finally the favorable layer and development area of hydrocarbon shales arepredicted.Favourable shale of Xiangzhong area is mainly developed in the Early Carboniferous,the Middle-Upper Devonian and the Permian. It is distributed in the upper of transgressivesystem tract, and the lower of high stand systems tract. Main shale development layer isC₁y～C₁d²、D₂q～D₃s and P₂. The most advantageous sedimentary facies for thedevelopment of the shale are the platform basin facies and the seamarsh facies.The shale’s evolution degree of Early Permian、the Middle-Upper Devonian in this areais high. The shale has the characteristics of high organic matter abundance, and the kerogentypes of the shale areⅠandⅡ. Ro value of the organic matter significantly incresead with thegrowing of the stratigraphic ages. For the same layer the evolution degree in western area ishigher than that in the east. In vertical, the Devonian enters into the mature stage fully.Theevolution degree of C₁y、C₁d¹is slightly lower, and parts of area have entered to high maturestage.The favorable shale mainly developed in Lianyuan basin and platform facies zone in thecentral of Shaoyang basin.According to the shale thickness, the Devonian and the Upper Permian, the developmentof Lianyuan basin is best.The layer of the largest effective thickness of shale is the UpperDevonian, followed by Early Carboniferous and Middle-Upper Devonian. The Permian shaleis the thinest. The exhibition area of effective shale is obviously decreasing from old to new,among which, the biggest area is the Upper Devonian, followed by Early Devonian and EarlyCarboniferous.The smallest is Upper Permian.The favorable area of the Lianyuan basin is lacated in the northern area, which covers allthe Lianyuan basin. The favorable area of the Shaoyang basin is lacated in the central areawhich covers most of the region in shaoyang basin center. The favorable area of the Lingling basin is located in Sourehern area which are distributed only in the center of the Lingyuanbasin.