Study On Productivity Model Of Fractured Horizontal Wells In Volcanic Gas Reservoirs With Natural Fractures

As a new exploration and development field,volcanic gas reservoir is rich in natural gas resources and has broad exploration and development prospects.However,compared with the conventional sandstone gas reservoir,the volcanic gas reservoir has more complex reservoir and seepage models,with multiple media including pores,caves and fractures,which determines the poor physical properties,complex seepage mechanism and difficult development of volcanic gas reservoir.Using only vertical Wells results in low effective reservoir production.In recent years,horizontal well production technology has been applied more and more widely in gas reservoir development,but there are usually problems of gas reservoir water breakthrough and gas well water production in gas field of horizontal well developed.Volcanic gas reservoirs generally have bottom water and complicated gas-water relationship,so water invasion is easy to occur and affect gas well production.At the same time,natural fractures are well developed in volcanic gas reservoir,which has an important effect on improving the productivity of the gas reservoir.However,there are few studies that consider both natural fractures and the effect of gas reservoir water production on horizontal well productivity.In order to solve the above problems,this paper firstly takes X low-permeability volcanic gas reservoir as the research object.Based on the geological situation of the gas reservoir,the seepage characteristics are summarized,using the principle of equal flow rate and dual media,it deduces the productivity equation in the form of pseudo-pressure without considering natural fractures and the influence of natural fractures.The non-Darcy flow factors included in the equation include stress sensitivity effect,start-up pressure gradient and high speed turbulence effect.The actual production data of two production Wells in P block of X gas reservoir were used to verify the productivity equation considering the influence of natural fractures,and the applicability of the equation was further verified by comparing the gas production of different productivity models.Secondly,the influence of natural fracture factors on the productivity of fractured horizontal Wells is analyzed by defining the parameter of gas well production improvement range,and the influence of geological parameters and engineering parameters on the productivity of fractured horizontal Wells is also analyzed.Finally,the orthogonal test method is used to rank the influence degree of artificial fracture parameters on the productivity model and put forward optimization suggestions.The following conclusions are drawn:The validation results show that the average error of gas production is 9.11%for two Wells,which proves the effectiveness of the productivity equation;The comparison results of the productivity models show that the average gas production error of the productivity equation derived in this paper considering the influence of natural fractures is less than that of the other three fractured horizontal Wells,which proves that the influence of natural fractures cannot be ignored in the production calculation of X gas field.Among the geological parameters,the stress sensitivity coefficient has a great influence on the production,and the influence degree is that the stress sensitivity coefficient of natural fracture is greater than that of artificial fracture than that of matrix.The effect of starting pressure gradient on production is small,and the effect of high-speed nonlinear coefficient becomes larger with the increase of production.When the value is greater than 10 m^-1,the effect of high speed nonlinear coefficient on production changes exponentially.The water-gas ratio has a great influence on the yield,and the yield decreases by58.87%when the water-gas ratio is 0.7 compared with 0.1.Among the factors of natural fracture,the increase of initial distance from wellbore and fracture distribution radius will increase the Increased range of production,and the influence of initial distance from wellbore is greater than that of fracture distribution radius.Fracture permeability and fracture width in a certain range have a significant impact on the increased range of production,that is,there is an optimal flow conductivity range.When the flow conductivity is sufficient,the smaller fracture density also has a significant effect on the increase of production.The orthogonal test results show that the importance order of artificial fracture parameters is as follows:artificial fracture number,artificial fracture permeability,artificial fracture width,artificial fracture half-length.At the same time,the optimal combination of each parameter is obtained.