History Matching of Naturally Fractured Reservoirs Using Elastic Stress Simulation and Probability Perturbation Method

Abstract

TX 75083-3836, U.S.A., fax 01-972-952-9435. AbstractThe application of elastic stress simulation for fracture modeling provides a more realistic description of fracture distribution than conventional statistical and geostatistical techniques, allowing the integration of geomechanical data and models into reservoir characterization. The geomechanical prediction of the fracture distribution accounts for the propagation of fracture caused by stress perturbation associated with faults. However, the challenge lies in estimating the past remote stress conditions which induced structural deformation and fracturing, the limited applicability of the elasticity assumption, and the latent uncertainty in the structural geometry of faults. The integration of historical production data and welltest permeability into geomechanical fracture modeling is a practical way to reduce such uncertainty. We propose to combine geostatistical algorithms for history matching with geomechanical elastic simulation model for developing an integrated yet efficient fracture modeling tool.This paper presents an integrated approach to history matching of naturally fractured reservoirs which includes 1) fracture trend prediction through elastic stress simulation, 2) geostatistical population of fracture density based on fracture trend map, 3) fracture permeability modeling integrating fracture density, matrix permeability and welltest permeability, and 4) numerical flow simulation and history matching. All of these implementations are incorporated into a single forward modeling process and iterated in the automatic history matching scheme. To obtain a history match on a reservoir model, we jointly perturb the large-scale fracture trend and local-scale geostatistical fluctuations of fracture densities rather than perturbing permeability calibrated from fractures. This strategy enables us to preserve the geological/geomechanical consistency throughout the history matching process. The geomechanically simulated fracture trend model is calibrated to both production data and geological structure map (faults and horizons) by finding the optimum remote stress condition for elastic stress-field simulation. The latter is achieved by matching the actually observed structural deformation trend with the simulated one. The smaller-scale fluctuation of fracture density is simultaneously history matched through the probability perturbation method of Caers (2003) 1,2 . The result of synthetic reservoir application is presented.

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“…Figure 10), which may result from the expansion of pre-existing fractures and pore networks in the clay, and (ii) decreasing intraclod permeability and porosity, which can be modelled (Tran et al, 2005;Denney, 2006;Sarma and Aziz, 2006;Donato et al, 2007;Suzuki et al, 2007).…”

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“…This sequence can be repeated several times. Although not shown in this work, LVM updates and PPM modifications can be also be done jointly 15 . A description of these workflows and their theory is given below.…”