Inversion of Production Data Using an Ensemble Smoother to Determine theGeometry of Hydraulic Fractures

摘要

The ensemble methods show the ability to obtain the geometry of natural fractures in high-permeabilityreservoirs. However, hydraulic fractures in unconventional reservoirs are different and the ability of thesemethods to invert production data to determine hydraulic fracture geometry is unknown. In this work,Embedded Discrete Fractures method is selected as the simulation method. The EnKF and EnRML methodsare chosen as the history matching methods. Several simulation cases are used to test these algorithms’performance in both conventional and unconventional reservoirs. Also, a novel gradient history matchingprocess has been proposed to solve part of the problems. By comparing history matching results of different cases, Ensemble methods’ matching quality is verysensitive with prior information. Production of wells in low-permeability reservoirs is not sensitive withthe unconnected fractures, which will lead to multiple minima in the objective function. It also causesbig difficulties in the estimation of the gradient for ensemble methods. Thus, it is even more important toadd prior information properly in the unconventional reservoirs’ history matching, which can narrow theproblem dramatically. The potential and limitation of using a gradient method to solve this kind of problemare also shown in this paper.