Application Of Modern Production Decline Analysis To Prefracture Assessment Of Refracturing Technology

Hydraulic fracturing is a major way to exploit tight gas reservoir. After long production, parts of fractured wells turn into a low yield period. Without taking infilling wells technique, refracturing technique is used to get fully potential of reservoir.Fractured wells in Chuanxi Tight Gas Reservoir can be classified into two types, which are completely failured wells and partially failured wells. In order to find out the causes of these two types of failured wells, parameters like reserves, fracture flow conductivity(cDF) and distance from well to the reservoir boundary(eDr) are resolved by using modern production decline analysis(MPDA) and analyzed to find out the cause of failured wells and select the wells capable of refracturing.According to gas flow theory of tight gas reservoir, solutions under constant pressure and constant rate were obtained respectively to describe infinite reservoir and circular confined reservoir. Type curves including Arps, Fetkovich, Blasingame, Agarwal-Gardner were plotted by using Matlab to analyze completely failured wells, and least squares method was employed to realize the fitting between field data and type curves.According to gas flow theory of fractured wells and MPDA in vertical fractured wells, type curves including Agarwal-Gardner, Pratikno were plotted to analyze partially failured wells and and least squares method was employed to realize the fitting between field data and type curves as well.Field geological data was used to establish a model in ECLIPSE, good fitting between the geological data by type curve fitting and field geological data used in simulation, demonstrating the validity of type curves.Fitting between production data and type curves were discussed under constant rate and periodical variable rate situation. Results showed that MPDA had a larger range than well testing in application. MPDA can be used to solve formation parameters accurately even if the pressure is variable and rate fluctuating.According to flow theory of fractured wells, a new series of type curves for vertical fractured wells were plotted using Pratikno dimensionless variable as coordinate. The impact factors on shape of type curves especially fracture half length and conductivity were analyzed, demonstrating that the two factor influence the shape together and big difference existed between high conductivity and low conductivity. The difference became smaller as the eDr increasing. Based on this differences, type curves can be used to distinguish the high conductive fractures between low conductive fractures.To discuss the time-sensitivity of fracture conductivity, the process of conductivity decreasing was simulated by applied ECLIPSE. Data from different periods were used to matching with type curves, and parameters like conductivity and eDr were calculated thereby. It is illustrated that type curves for vertical fractured wells based on MPDA can be applied during production anytime and the calculated productivity and eDr in different period were different. Type curves can be applied in prefracture assessment, monitoring the failure process of wells conveniently.Studies showed that rate and pressure data which are easily available can be used in MPAD to carry on prefracture assessment in tight gas reservoir. Research on MPDA for vertical fractured wells means significant to prefracture assessment in refracturing. The method can be also applied in all prefracture assessment.