| The south-central area of Sichuan is located in the moderately gentle belt of the Middle Sichuan uplift,in the north of the Moxi and Guang'an Gas Fields,and borders Huaying Mountain.It is close to the middle and low steep bends of the ancient Qianlong Middle Sichuan and the middle and high steep faults of the East Sichuan.Pleated ribbons.Drilling examples demonstrate the well-developed reservoirs in the Qixia Formation in the south central part of Sichuan,and the Lower Permian dolomite discovered in the study area is a reservoir.However,the understanding of the mechanism of formation,distribution and distribution of dolomite reservoirs in the present study area is unclear,and the gas-bearing nature is unknown.It is impossible to predict favorable areas for oil and gas exploration and restrict the exploration and development of gas fields in the study area.This paper comprehensively uses well logging,geology,seismic and drilling core data to carry out studies on stratigraphic division,type and characteristics of sedimentary facies,dolomite reservoir characteristics and major diagenesis,and prediction of the distribution of favorable areas for reservoir development.Obtained the following achievements and understanding:(1)The boundary sequence interface of the Permian strata in the study area was re-identified,and 8 of the sequence interfaces were identified in the Lower Permian strata.The Qixia Formation in the study area contains two third-order sequences:sequence 2(PSq2)and sequence 3(PSq3).Sequence 3 corresponds to the second section of the Qixia Formation in the study area.The lower type ? sequence interface is a lithological conversion interface,and the mudstone-powder-mucky limestone is gradually converted to gray-brown gray algae limestone..The Habitat B submember is dominated by mudstone micrites,and lamellar algae ash is trapped.The subdivision A2 has developed a thick layer of gray and light gray algae sandstones with sand inclusions.The lithology from the mudstone and shale to the carbonate rock at the interface between sequence 1(Liangshan Formation)and sequence 2(habitat).(2)The Qixia Formation as a whole belongs to the open sea-Taiwan sediments,and the Habitat 2B sub-segment is an open sea sub-facies sedimentary.It is dominated by mudstone micrites,and is covered with a thin layer of algal limestone;the second habitat stage is the Qixia Formation Sea.At the time of the largest retreat,the water body was shallow and the wave washing effect was strong.A thick layer of gray and light gray algal sandstone was developed,and the sand debris was observed.The second part of the Qixi Formation is the main beach-forming period and the grainy beach develops over a large area.The rest of the section is dominated by open-sea sediments,with locally developed granular beaches.(3)In the study area,dolomite is mainly developed in the second member of the Qixia Formation,and is mainly dominated by "sugar and granular" dolomite.The caves,dissolution joints,dissolved pores,intergranular(solution)pores and intergranular(solution)pores develop and are high quality reservoirs.The fracture-hole type reservoir is characterized by low porosity and low permeability.In the plane,the second part of the Qixia Formation develops in the Moxi-Longnusi area,with stable development of 2 to 4 layers,and the effective thickness is generally 2 to 5 meters.Thickness 3 to 15m.The second member of the Qixia Formation dolomite in the Moxi and long nv monastery area is formed by the burial hydrothermal cloud of the granular limestone.The development of the high quality reservoir is controlled by the sedimentary facies of the pellet,and the dissolution is the main factor to improve the reservoir ability.(4)According to the "strong valley" inside the Qixia Formation,which is the seismic response characteristics of dolomite,combined with sedimentary understanding,it is suggested that the Moxi-Longnusi area is a favorable area for the development of the Qixia Formation dolomite reservoir. |
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