The Tectonic Evolution Of Leshan-Longnvsi Paleo-uplift And Its Controlling Effects Upon Gas Reservoir Forming In Sinian Strata

Leshan-Longnvsi paleo-uplift is a giant irregular structural nose developed underPermian in the central and western of the Sichuan Basin, covering an area aboutone-third of the basin, which is an important area of gas exploration. On the basis ofprevious work, the paper using the latest high-precision seismic data, logging data anddrilling data to interpret the paleo-uplift's structure and describe its morphology. Itsystematically discussed the features of unconformities, established the tectonicsequences and restored paleo-uplift's tectonic evolution and deeply analyzed theeffects of the evolution on Sinian gas accumulation, pointed out the favorableexploration area. The research achieved the following results and understanding:(1) Using the latest seismic data and drilling and logging data to interpretstructure accurately and describe structural features of 9 strata meticulously.(2) The paper pointed out that the paleo-uplift has horizontal partitioncharacteristics clearly first time. Structures in western Sichuan area are smaller thanother area and the folding and faulting is relatively strong. The Weiyuan fornixanticline is the main structure of the Weiyuan area, and the Ziyang small nosing foldgroup locates on the north side of it. The overall tectonic deformation of central areais weak and the structures from north to south can be further divided into three rows.(3) The paper systematically analyzed the major unconformities'structuralfeaturesof the paleo-uplift, proposed and used the method of'spatial trendextrapolation'to restored the eroded amount of Tongwanian, Caledonian andIndosinian unconformities. According to the featuresof unconformities of thepaleo-uplift, the region strata were divided into which has six level-1 and 13 level-2tectonic sequences.(4) Based on the features of unconformities and of the tectonic sequences, theevolution of the paleo-uplift was divided into four stages: the embryonic stage, thedevelopmental stage, the stable burial stage and the adjust-shaping stage. Thesignificant tectonic deformation of Leshan-Longnvsi paleo-uplift occurred duringCaledonian movement Taconian episode. During the Silurian Period to the Permian,the paleo-uplift occurs only lifting movement as a whole, there is no obvious structural deformation.(5)Studies have shown that the paleo-uplift's tectonic framework of thedifferent periods restrained the the matching of source rocks, reservoir and traps intime and space, establish the gas accumulation model of Sinian(6) Gaoshiti area is long-term structural high since Sinian. It has entire structuraltrap and sufficient gas source, is the most favorable area.