Study On Reservoir Characteristics And Controlling Factors Of Ma 5 And 1-2 In The Southwestern Part Of Yulin Gas Field

Located in the Northeast of the Ordos Basin,Yulin gas field is one of the main gas fields of Changqing Oilfield Company,PetroChina.Yu37 well block is in the southwest area.Preliminary production test in Majiagou formation of the Lower Paleozoic in the region of interest indicates its promising development potential,but lack of basic geological research,thus further exploration of the reservoir characteristics and controlling factors of the area is of vital significance in fully excavating the development potential and expanding production scale for Yulin gas field.Focused on Mawu1-2(M1-2)sub-segment and based on the predecessors,with theoretical guidance of the reservoir geology and sedimentology,using drilling,logging and analysis data as foundation,the paper conducted an intensive research on the zone of interest in regarding of its reservoir lithology,reservoir type,pore texture characteristics and controlling factors.Also the paper evaluated and forecast the reservoir's range of profitability.The intended interval was divided by strata correlation and electrical characteristics of the rock.The M1-2 sub-segment reservoirs in this area is identified to made up of denudation vug dolomite,crystalline dolomite and other types of carbonate rocks with the help of cores,flakes and logging data.The main ingredients filled in the reservoir space are gypsum concretion dissolved pore,gypsum crystal pore,intercrystal pore and intercrystalline dissolved pore.The reservoir is low porosity and permeability with strong heterogeneity.Effective reservoir is mainly distributed in M,sub-segment,followed by M2 sub-segment.Factors dominating reservoir development are sedimentary microfacies,diagenesis,tectonic and karst palaeogeomorphology.The micro sediment facies of gypsum mode and gypsum concretion on the superatidal zone are favorable sedimentary microfacies;The dissolution period of the epigenetic rock and burial dissolution determine the reservoir quality,while the calcsparite is the most devastating void cement;The distribution of gas reservoir is significantly affected by the structure,with favorable reservoir concentrating in up dip of the structure.Physical manifestation is that a positive is superior to a negative;paleokarst reservoir is more integrated reserved,the ancient terraced hills and platform edge slope overpass depression.Considering manipulating factors of the reservoir,combined with pore throat structure and physical properties of each production formation,to establish the evaluation criteria for the area,the favorable reservoir of the M1-2 sub-sections in this area is divided into I.II.III categories,further refined as five sections for seriatim evaluation to provide reference for the future exploration and development.