Study on Triassic Fin Delta Sedimention and Reservoir in Lunnan Area Tarim basin

Being influenced by Landei Fracture of Triassic in Lunnan area,the elevations in the both sides on the fracture are large enough to make the alluvial fan to enter directly the lacustrine basin and to form the fan delta group deposition. The fan deltaic body can be divided into three subfacies, named fan delta plain, fan delta front and pro-fan delta. Subaquous distributary channel sand bodies in the fan delta front are mast important reservoir of oil and gas. The developing area of reseroir is located at SangTamu Horse Belt and the southern ppart. The kinds of reseroir rock are maiNy fine-coarse grained lithic sandstone with lower maturity of the mineral and texture, containning quarts 15 ~6 0%, feldspar 10~25%, rockclast 35~75%. The most important reservoir space is secondary solution pore,including intergranular solution pore, intraparticalar solution pore,oversize pore,cement-dissolved pore,secondly micro-pore, primary pore and fissures. The Triassic reservoir are characterized by deep burial,high porosity and good permeability,burial depth 4200-r5400m,porosity of 15-28. 45%, permeability of 10~4317. 9 X 10^-3μm². Finally the origin of high porosity and good permeability of Triassic reservoir is discussed under such a burial depthi: 1. Coarse grain reservoir sediments;2. Usually less than 5%of clay content; 3. With thick mudstone (12~175m)between sandbeds;4. Increasing reservoir space because of the clastic grain dissolved by organic and inorganic acids;5. Most kaolinite is of porphyritic texture,so it is not easy for them to fill the pore and throat;6. Lower geothermal gradient and deep burial in high speed and short period, etc.