The Characteristics And Main Controlling Factors Of Gas-water Distribution In The 5^th Section Of The Xujiahe Formation In Western Sichuan Depression

The 5th sector of the Xujiahe formation(T3x5)in western Sichuan depression is the typical unconventional gas reservoir,which is recognized with great resource potential and exploration prospect.However,its exploration and development process has been severely restricted by the complicated gas-water distribution relationship.For further study on the T3x5 of the study area,based on previous research,this paper has analyzed the fluid geochemical characteristics and genetic types,established the gas-water layout on the plane and typical well profiles separately,made clear the gas-water distribution characteristics of the typical region,and also revealed the main control factors of gas-water distribution combined with the mathematical geological analysis,through the use of drilling,logging,seismic,integrated interpretation,testing data,and the conventional experimental analysis data from abundant gas or water samples,etc.Research has shown that,for the T3x5,the gas is classified as typical pyrolysis coal type gas,and the formation water appears as calcium chloride type water on the whole,which formed by the mixture of desalted formation water,condensate water and residual acid water,and meanwhile reflects the reductive environment in the proximal;on the plane,the high yield gas wells are mainly concentrated upon the structural high position,but the high yield water wells gradually close to faults;on the profile,gas bearing layers are widely distributed,of which most are fractured gas bearing layers that mainly concentrated in the upper or lower section,while gas-water contained layers or gas bearing water layers are less and mainly concentrated in the central section;the formation water is generally distributed as "isolated island" and "layered",among which only local appears as horizontal continuous phenomenon,but there is no obvious gas-water interface on the longitudinal;for a single well,the gas acquiring high yield mainly depends on thick shale,developmental distributary bay microfacies,low sand-mud ratio,low pressure,high TOC,high porosity,and high fracture density,while the water obtaining high yield is mainly controlled by thick shale,sand-mud interbed,developmental underwater bar microfacies,close fault distance,and high pressure;the main controlling factors of gas bearing capacity contain TOC,pressure,and porosity,which of water bearing capacity include pressure,fault distance,distributary channel microfacies,and shallow-lake mud.