Research On The Productivity Of Fractured Horizontal Wells In Tight Reservoirs

Due to the low permeability of tight oil reservoir,vertical well used to develop tight oil reservoir generally has no natural productivity,so fractured horizontal well is often used to develop tight oil reservoir.In order to improve the accuracy of the fracture construction parameter design of horizontal well and the development benefit of fractured horizontal well,study on productivity model of fractured horizontal well is needed.A tight oil reservoir in ordos basin is selected as the research object.Through the indoor core experiment,establishment of theoretical model and flow regime identification method,the analysis and optimization of the influence factors of fractured horizontal well productivity and forecast of fractured horizontal well productivity is studied.The following work has done and some conclusion is obtained:(1)The stress sensitive experiment under formation condition shows that the average exponential stress sensitive coefficient of sandstone sample in H wellblock,J wellblock,L wellblock and W block were 0.0073 MPa-1,0.0205 MPa-1,0.0244 MPa-1 and 0.0163 MPa-1,which demestrate the existence of the permeability stress sensitity in tight oil reservoir.(2)Based on the conformal transformation method and superposition principle,the steady-state productivity model of fractured horizontal well in tight oil reservoir is deduced,and a calculation example is given.The calculation results are compared between other classical steady-state model and the steady-state model deduced in this paper,which demonstrate that the deduced model have a smaller error and higher precision because of the consideration of stress sensitivity.(3)The influence of stress sensitivity coefficient,fracture nμmber,fracture length and fracture conductivity on productivity of fractured horizontal well is analyzed by using the deduced steady-state model.The daily oil production increase with the increase of fracture nμmber and of the fracture conductvity,while the increase range become lower.Under the same fracture conductivity,the productivity increases with the increase of fracture length.The daily oil production is linear increase with the increase of fracture length.With the increase of stress sensitivity coefficient,the decrease range of productivity also increased under the same differential pressure,and the increase of differential pressure lead a bigger decrease range of productivity,so it is necessary to maintain a reasonable differential pressure.(4)The seepage process of fractured horizontal well will resulted in corresbonding flow regime.The flow regime identification method is used to analyze the flow regime characteristics in the production process.Based on flow regime characteristics,the corresponding productivity equation is established,and the unsteady-state productivity forecast model of fractured horizontal well in tight oil reservoir is obtained by coupling with the productivity equation.(5)By using unsteady-state productivity model deduced in this paper and designing a fractured horizontal well in each type of formation at the four well block,the influence factors of productivity is optimized and the optimμm values of each influence factors is obtained.The influence of stress sensitivity upon fractured horizontal well is analyzed.When produced in a certain bottom hole pressure,the change of stress sensitivitiy coefficient only contribute to a relatively high or low productivity,which have no effect on the decline trend of productivity.The research results in this paper can provide a reference to the forecast of productivity,the determination of work system and the design of fracturing parameters.