Research On Reservoir Characteristics And Damage Mechanism Of Yinggehai Formation In DF1-1 Gas Field

The most of loose sandstone oil and gas resources belong to high porosity and high permeability reservoirs.However,some of them have poor physical properties low permeability reservoirs with relatively high shale content and fine rock grains,such as argillaceous siltstone and silty mudstone,etc.This kind of low permeability reservoir is very common in offshore oil and gas exploration in China,such as DF 1-1 gas field in the South China Sea.In offshore gas field exploration,the low permeability reservoir is restricted by working environment and cost,the number of drilling platforms and development wells is limited,and the basic data of coring wells and core analysis are few,leading to incomplete understanding.And in various operations,often due to incorrect protection measures,resulting in low or even no production of gas wells.Aiming at the main problems existing in the development well of loose sandstone gas reservoir in Yinggehai formation in DF1-1 gas field in South China Sea,this paper analyzes the characteristics of reservoir lithology,physical property and pore structure in depth by means of various analytical tests.Through laboratory experiments,the main damage mechanisms and types of reservoir in the process of production and drilling and completion are evaluated,the main causes of low yield and low efficiency of loose sandstone reservoirs are identified,and the effective plugging removal measures are recommended to provide the basis for efficient exploration and development of gas fields.The research shows:(1)The Yinggehai formation of DF1-1 gas field in South China Sea belongs to shallow water-semi sea sedimentary environment,?U,?L and ?U gas groups are belong to turbidite sand sedimentary environment,and the I gas group is belong to foreshore dam sedimentary environment.(2)The second section of the Yinggehai Formation is mainly composed of powder-fine quartz sandstone,followed by muddy siltsone.The content of the filler is mainly composed of mud,the average concentration is 21.86%?42.90%,and the clay minerals are mainly composed of illite and montmorillonite.(3)The porosity of the reservoir is mainly distributed in 25%?30%,the permeability is between 10mD?100mD,and the whole is high porosity and middle permeability reservoir.The physical property of ?U was the best,followed by ?L and ?U,the I gas group was the worst.(4)The reservoir space of Y2 section is mainly intergranular pore,followed by a small amount of intragranular pore.The average pore throat radius of gas reservoir is 0.78-1.54?m and the maximum pore throat radius is 8.83-28.76?m.Overall,the reservoir throat is small and the connectivity is poor.The gas layer of Y2 section is divided into four types,and the type II reservoir is mainly.(5)The main damage mechanism of the Yinggehai formation in the process of drilling and completion is that the organic solid-phase demulsifier is incomplete,which leads to the blockage of the pore throat.In the process of production,the main damage mechanism is water lock.(6)After analyzing the causes of the typical low-efficiency gas wells,it is recommended to use surface-active agents combined with matrix acidification deblocking measures to relieve formation damage.