Transient linear flow analysis of constant-pressure wells with finite conductivity hydraulic fractures in tight/shale reservoirs

Abstract

Abstract Transient linear flow is the dominant flow regime in many multi-fractured horizontal wells completed in very low permeability reservoirs. Therefore, development of reliable methods for analyzing production data from this flow regime is of great value. The common methodology for production analysis of this flow period is use of square-root-time plot in which normalized pressure (or pseudopressure for gas) is plotted vs. square-root-time. This method has been proved to be acceptable for systems with infinite conductivity hydraulic fractures. The square-root-time plots for such systems exhibit a zero intercept. When analyzing production histories of real examples, we observe cases for which the square-root-time plot exhibits a straight-line trend with a positive intercept. We demonstrate that this behavior can be attributed to systems with finite conductivity hydraulic fractures. For constant-pressure systems with finite conductivity hydraulic fractures, the square-root-time plot methodology overestimates fracture half-length. This has been shown using synthetic examples. To solve this problem, we have developed a new inverse solution methodology which is based on an analytical formulation. We have defined new plotting functions and illustrated that a plot of these functions against each other in the formation linear flow period exhibits a linear trend. From the slope of this plot, the true value of fracture half-length can be estimated. Also, fracture conductivity can be determined from the intercept. The proposed methodology has been verified using synthetic tight oil examples. We have also applied it for several tight gas examples. We have analyzed production data for two field examples using the conventional square-root-time plot methodology and the new inverse solution methodology. Our analysis reveals that the square-root-time plot methodology considerably overestimates the fracture half-length for these examples.