The Reservoirs Characteristics Of The Mid-triassic Leikoupo Ormation, In The Central Segment Of The Western Sichuan Epression

There are widespread carbonate reservoirs in the Sichuan basin, as an importantreservoir of natural gas. However, the strong heterogeneity and multiple controllingfactors in the reservoir make it difficult for petroleum exploration in the westernSichuan basin. Based on the geological, geophysical and geochemical analyses etc. inwells and outcrop, we have studied the reservoir characteristics of the middle TriassicLeikoupo formation in western Sichuan depression.The facies of Leikoupo formation is predominant with the restricted platform,open platform, subordinate with evaporation platform, including such microfacies:subtidal, platform inner bank, platform marginal bank, alga arenitic bank, lagoon,salinization of the lagoon lake, gesso lake, gesso basin, algae-mud flat and tidal channel.There are Hanwang bank and Dujiangyan bank of the Leikoupo formation in the studyarea. Hanwang bank in the first member,second member and fifth member ofLeikoupo formation.Dujiangyan bank in the first member,second member,thirdmember and forth member of Leikoupo formation.As geophysics in three-dimensionalwork area, it is characterized with low continuity, low frequency, weak-to-mediumamplitude, gentle biasand and hummocky seismic reflection for the bank facies in thefourth member of Leikoupo formation, e.g. Xiaoquan bank, Majing bank andXinchang-Wenxing bank.The Leikoupo formation had constructive and destructive diagenesis in the studyarea.The constructive diagenesis of reservoir pore in Leikoupo formation arekarstification, dolomitization and fracturing, in contrast to the destructive diagenesis including compaction, pressure solution, cementation, recrystallization and filling.The reservoir rocks in the Leikoupo Formation are dominantly composed ofclastic dolomite, crystal grain dolomite, clastic limestone and crystal grain limestone.It is characterized of low-density, middle-to-high speed, low acoustic impedance,low-resistivity and high neutron porosity in the electrical feature of logging in thethird and fourth members of Leikoupo formation in Well Chuanke-1. However, theelectrical features of logging are low gamma, high-speed, relatively high resistivity,higher density and high wave impedance in the third members of Leikoupo formationin Well Longshen-1.The types of reservoir pore are intergranular pore, intergranular pore and fracture.The third and fourth members of Leikoupo formation have a low porosity andpermeability with theⅡand Ⅲ types of reservoir, which are better than that of firstand second members. It is characterized with theⅡand Ⅲ types of reservoir in thethird and fourth members of Leikoupo formation in Well Chuanke-1. However, thereservoir in the third member of Leikoupo formation is dominant with tⅡhetype, andsubordinate with theⅢ type in W ell Longshen-1. In particular, the reservoir of thefourth member is predominant with Ⅳ type, only partial Ⅲ type. Compared with theregional tectonics, we concluded that the different uplift and exhumation in the earlyof Indosinian has resulted in much stronger paleokarst in Well Chuanke-1located inXiaoquan than Well Longshen-1in Dayuanbao areas. Thus, it suggests that paleokarstis the most important controlling factor of high-quality reservoir in western Sichuandepression.There are three types of high-quality reservoir in the middle Triassic Leikoupoformation in the central segment of the western Sichuan depression as follows: reefand bank reservoir, karst reservoir and hydrothermal dolomite reservoir. Which werepredominantly under the control of facies, diagenesis and tectonics.