Productivity Prediction Of Hydraulic Fracturing In Tight Oil Reservoirs

With the rapid development of economy in our country,the conventional oil and gas resources supply are dwindling and the contradiction between supply and demand is lager and lager.However,the reserves of tight and unconventional oil are abundant for which they are practical substitution for conventional oil resources.The developing of tight oil reservoirs is achieved in virtue of the horizontal well technology and the large scale hydraulic fracturing measures.But there are still some problems such as the unclear understanding of the seepage characteristics,the shortage of reliable productivity prediction model and the determination of the scope of use in current studies.Thus,revealing the seepage law of horizontal volume fracturing wells,establishing the partition productivity prediction model of horizontal volume fracturing wells and determining the scope of use are extremely significant for accelerating the development of tight reservoirs as well as changing the national energy strategy.In this paper,the physical model of volume fracturing and the prediction model of composite partitioning productivity of horizontal wells in tight reservoirs are described and established.The internal area of the model is the double medium comprised of the fracture network which is founded by the coupling of artificial fractures and natural fractures and the matrix while the external area of the model is a single substrate.The effect of start-up pressure gradient,pressure-sensitive,capillary force and the losing efficacy of artificial fractures during production process are completely considered in this model.The continuity of flow is utilized to deduce the flow relationship between the double medium reservoir and the artificial fractures as well as fractures and the wellbore.The coupling relationship between the reservoir,the fractures and the wellbore is founded with the reservoir-fracture and fracture-wellbore flow switch.The solving Jacobi Matrix of fracture-reservoir-wellbore coupling model is built with the treatment of fully implicit difference method on the basis of the above.The N-R iterative approach is used aiming at solving the reservoir,fracture and wellbore parameters concurrently.The correctness of the model was validated by comparing its solving results with that of the Eclipse software.The influence of the fracturing cluster number of each stage,the stage number of fracturing,the half length of fractures,the permeability of transforming volume and the fracturing volume on the productivity of horizontal volume fracturing wells are analyzed.The numerical simulation method is used to analyze the characteristics of the use of different well types in tight reservoir as well as the affecting factors of the use area of the horizontal volume fracturing well,with which the major factors are screened out.Combining with the influence of various factors of horizontal well on use area,the reasonable row spacing of the water injection of the horizontal volume fracturing well in the tight reservoir can be determined.Take account of the feature that the single well productivity is decreasing rapidly in the development process of the horizontal volume fracturing well in the tight reservoir,the water injection measure is taken for the development of the horizontal volume fracturing well to refer the method of enhancing the single well productivity of water injection swallow and optimize the water injection parameters in this paper.With the theoretical analysis and the numerical simulation study in this paper,the horizontal well seepage characteristics of volume fracturing in nearly well zones which is acquired,the establishment of horizontal well productivity prediction model of tight reservoirs and the using radius method for volume fracturing of tight reservoirs as well as the tragedy for improving the productivity of a single well can play a guiding role in the effective development of the tight reservoirs.