Study On Water Invasion Mechanism And Fracturing Well Productivity Model Of Heterogeneous Gas Reservoir

Natural gas resources is characterized by small environmental pollution and huge reserves.China is rich in natural gas resources,but most of the gas reservoirs that have been developed have experienced water invasion,especially the edge and bottom water invasion to varying degrees.The research and understanding of the gas reservoir drived by water has become an important subject for the serious influence of the water invasion.The diversity of gas reservoir space and the strength of heterogeneity will directly affect the formation water intrusion characteristics.The heterogeneity of gas reservoir will result in the heterogeneous water invasion and the formation of a large number of water-sealed gas in strata.At present,the fracturing of high water-cut gas wells has been adopted to achieve water control and stable production.After fracturing,near-wellbore reservoir fluids are redistributed,The natural gas and water near the well are pushed back to the foramation by fracturing fluid and fracturing sand.Due to the low viscosity,fast flow rate and low starting pressure of natural gas,after the well is opened,the natural gas flows into the wellbore quickly bypassing the water body at the edge of the well,temporarily forming the "gas seal water",resulting in the temporary non-flow of the edge water and the reduction of the water yield of the gas well.The fracture produced by fracturing is helpf'ul to improve gas permeability,change gas-water two-phase percolation characteristics and increase the two-phase co-percolation area,thus prolonging gas well production time and enhancing gas reservoir recovery efficiency.In this paper,TN heterogeneous gas reservoir in Qaidam basin is taken as an example.This paper summarized and analyzed the percolation mechanisn and two-phase percolation characteristics on the basis of the research of a large number of water invasion literatures at home and abroad.Based on the field production and core experiment data,this paper investigated the change of reservoir permeability and the production decline rule after water invasion.This paper analyzed the microscopic water invasion mechanism of gas reservoir.The visualization experiment of-water drive gas in heterogeneous gas reservoir is carried out qualitatively and quantitatively from the macroscopic perspective by establishing the indoor physical seepage model.This paper researched the influence of water invasion by changing the water invasion velocity and displacement pressure and found that the water will permeate along the highly permeable zone and the actual situation of the gas reservoir.This paper also found that the heterogeneity in the longitudinal will have a bigger impact on the gas recovery.On the basis of the previous productivity model of fracturing gas wells and defining the gas-water two phase generalized pressure that considered the effect of stress sensitivity,this paper built the gas-water two-phase productivity model for fractured gas wells and proved that it is applicative in TN gas reservoir.This paper also analyzed the effect of the water-gas volume ratio,the length of-the fracture and the stress sensitivity index to the productivity.The study in this paper is of certain sig,nificance for understanding the water invasion rule of heterogeneous gas reservoirs and guiding the field production and development.At the same time,it is indicated that adopting reasonable production work system and certain stimulation measures will help improve the recovery rate of heterogeneous gas reservoirs.