Evaluation Of Development Effect Of Bedrock Gas Reservoir In Dongping 1 Well Area

The exploitation of unconventional gas reservoirs has been increasing in the proportion of oil and gas production year by year,especially the exploitation of bedrock gas reservoirs.This kind of gas reservoir is famous for its complex reservoir physical property and strong heterogeneity.It is difficult to develop effectively by using conventional reservoir description technology and production technology.Moreover,the bedrock reservoir with bottom water is more likely to have rapid water appearance and large productivity decline speed.Dongping gas field is a rare mass gas reservoir in bedrock buried hill at home and abroad.The distribution of gas and water in this field is basically controlled by structure.The reservoir in bedrock section has a unified gas-water interface.Moreover,fractures are developed,which are not only the main channel for gas seepage,but also the channel for bottom water to invade into gas reservoirs.Four years after the development of this block,the prominent problem in the production is that the water yield of some gas Wells increases sharply within a short period of time,resulting in the continuous decline of gas well production and the increase of the number of water-flooded Wells at the structural edge.Moreover,the geological reserves in the region need to be re-verified.There is no accurate gas-water interface and no accurate evaluation of the water energy.These problems seriously affect the adjustment and implementation of the next development plan.To solve the above problems,based on the results of three-dimensional geological modeling of bedrock gas reservoir and numerical simulation of dual pore medium,combined with the production dynamic data of the study area,a set of methods for evaluating the development effect of water-invaded gas reservoir and scientifically controlling water and increasing production were developed in this paper.The research results are as follows:1.The original geological reserves of Dongping 1 well area have been verified again.The material balance method is used to verify the single well control reserves after water invasion.Under the existing mining methods,the economic recoverable reserves are determined by the production decline analysis method and the pressure decline method.2.The formation pressure in Dongping No.1 well has decreased greatly,and the average pressure of the gas reservoir is about 27MPa.The output showed the law of hyperbolic decline,and the initial decline rate Di=0.23mon-1.3.Based on the actual production dynamic data of the gas reservoir and the high-pressure physical property data of the fluid,the water invasion coefficient of the gas reservoir in Dongping Area 1 was calculated as 21,666.7m3/MPa,and the overall water energy was relatively weak.According to the calculation,the current water drive index is considered to be a medium elastic water drive gas reservoir.4.Dongping No.1 well area presents three water invasion characteristics:large seam,small seam and transverse seam.Bottom water invades in the east and south,and water invasion is serious in the east.Bottom water coning along the direction of a single well,the whole bottom water interface has not been uplifted.5.The simulation method and numerical simulation method are adopted to confirm that the current reasonable gas recovery rate in the study area is 2%,but the actual gas recovery rate is too high.The single well production capacity method and interference test method implement that the reasonable well spacing in vertical Wells is 750m-800m,and the reasonable well spacing in horizontal Wells is 900m-1000m,and the well pattern of Dongping 1 gas reservoir is relatively reasonable.6.Determine that depletion mode combined with drainage gas recovery is adopted in Dongping 1 well area:The reasonable daily gas output of depletion mode is 97.73×104m3/d,the displacement of small-seam vertical Wells is 101.60m3/d,the displacement of small-seam horizontal Wells is 80.60m3/d,the displacement of large-seam vertical Wells is 211.11m3/d,and the displacement of large-seam horizontal Wells is 166.50m3/d.The technical achievements formed in this study enrich the evaluation content of the development effect of unconventional gas reservoirs in China,can guide the adjustment of gas field development plan with similar geological characteristics,and can provide relevant research experience for the study of other bedrock gas reservoirs.