The Research Of Petroleum Geology Conditions In The T₁f¹ Of The Lower Triassic, Nanchuan Area

Based on the research results of the measured sections in the field, the s tudy adopted the research method of combining geological, geophysical and ge ochemical to do the reasearches for major hydrocarbon source rocks(Longtan f ormation) petrology, sedimentary facies and hydrocarbon source rock characteris tics, as well as regional sedimentary evolution characteristics, lithology, sedimen tary facies types and the distribution characteristics of the reservoir(the possibl e reef flat) and reservoir physical properties of the T1f1 of the lower Triassic in the Nanchuan area,and at the same time combined with structural styles and trap characteristics to explore the oil and gas geological conditions of the T1f1 of the lower Triassic in the Nanchuan area.Nanchuan area is located in the southeast of Sichuan basin and the north west of the Dalou mountain area.Nanchuan area relatively developed folds and faults.The compressional structural surface folds and faults surface are mainly d istribution in the direction of N-NN,SN and NW directions developed as well and the partial area developed arcuate structure.From WN to EN,the folds Cha nging trending in the Nanchuan area showed the major trend is that from the ejective folds which have narrow anticline and broad synclines become the wi de spaced synclines which have broad anticline and narrow synclines.The evolution processes of the Yangtze platform have multiple stages, in g enerally, there are seven times, including:Xuefeng movement(Z), the early-mi d caledonian stage(∈-O), the late caledonian stage(S), Hercynian(D-P) stag e, Indo stage, Yanshan and Himalayan stage.Superposition of tectonic movemen ts of the Yangtze platform, resulted in complex structures.Longtan formation in the Nanchuan area is the main source rock of T1f1. Longtan formation mainly developed during the deposition:eluvial plain Sedime ntary system, lagoon(Gulf) tidal flat Sedimentary system and carbonate platfor m Sedimentary system. Lagoon(Gulf) tidal flat sedimentary facie take the subject position. TOC content of Black, gray-black shales in the mud bog, peat sw amps, lagoons(Gulf) sedimentary microfacies is relatively high and beyond the lower limit standard of source rocks, as well as dark-gray micrites in the rest ricted platform subfacie. Ro is greater than 1.35%, the evolution of source roc ks reached a mature stage.Mud and shale rocks of Longtan formation is the m ain source rocks and some micrites have hydrocarbon potential.Feixianguan formation in the Nanchuan area is sedimentary carbonate platf orm, developed restricted platform and open platform subfacies. T1f1 develops o pen development platform subfacie, including inter beach microfacies, oolitic be ach microfacies, bioclastic bank microfacies and micro-sand beach with crumbsmicrofacies.The inter beach microfacies’ main lithology is argillaceous limeston e, microcrystalline limestone, dolomitic limestone and shale. The oolitic beach microfacies mainly develop oolitic limestone, calcarenite and bioclastic limeston e. Argillaceous limestone and limestone particles have better reservoir physical property.The average for the study area are Ⅲ reservoir reservoirs(poor reserv oirs), but partial reservoir can be achieved forⅠ-Ⅱ.The north and south part’s porosity and permeability is better, owning certain conditions for forming rese rvoir, and in the eastern part, its porosity and permeability conditions is very poor, and belongs to non-reservoir.The reservoir spaces of Nanchuan area includes Primary intergranular pore,dissolution, holes, seams, intergranular pore and fracture,The most important reservoir spaces are dissolution pore and fracture. The reservoir physical proper ty of T1f1 is mainly controlled by original depositional environment,and the d iagenesis like compaction pressure solution, dolomitization, dissolution, packing action, cementation, recrystallization, tectonic disruption. cementation, packing action, compaction pressure solution, recrystallization will reduce the porosity a nd permeability of the reservoirs, and dissolution, dolomitization and tectonic di sruption increases porosity and permeability.The direct cap rock overlying T1f1 is purple mudstone, marlstone, lime mu dstone, dolomitic limestone of T1f2 tidal flat microfacies which thickness is 120 meters or so, forming cap beyond the reservoir. The cap’s thickness is relati vely higher and distributed widely.The trap type in the Nanchuan area is struct ural-lithologic trap. The faults have closed by the lateral thrust fault’s pressure surface and fault smear effects.The trap in the study area is made up of anticli ne, T1f2 cap rock and the lateral thrust fault.Through the comprehensive analysis of the conditions of the source rocks, reservoir, cap rocks and trap, the petroleum geology conditions of T1f1 in Na nchuan area has been made a comprehensive Evaluation. In generally, the cond itions of source rocks, cap rocks and trap in T1f1 are pretty good, but reservoir condition is poor.