A Streamline-Based Method for Assisted History Matching Applied to an Arabian Gulf Field

Abstract

Abstract We present a streamline-based history matching method that overcomes two of the major limitations of previous approaches:it uses a three-phase compressible streamline simulator for the forward simulation, and so its application is not limited to incompressible waterfloods; andgeological constraints, such as regions of differing facies, can be honored. Permeability, porosity and anisotropy can all be modified using the methodology of Assisted History Matching.1–3 In this paper the technique is extended with suggested modifications to the reservoir description computed assuming tracer-like flow. This allows the engineer to direct the parameter changes through interactive code. The method is applied to history matching the full field model for the Southwest Fateh Mishrif field located in an offshore concession in the Emirate of Dubai. The Southwest Fateh Mishrif is a carbonate reservoir containing a highly undersaturated oil. There are currently 42 active producers and 27 active water injectors. First production occurred in 1972 and waterflooding commenced in 1975 prior to the field average reservoir pressure falling below the bubble point with present injection rates of 320,000 BWPD. Introduction A number of streamline-based methods for history matching have been proposed (for recent papers on this topic, see, for instance1–16). Streamlines identify the instantaneous flow directions and the regions of the field that are flowing to each production well. As a consequence it is possible to identify what parts of the reservoir impact the flow to each production well and hence the permeability and porosity of these regions can be adjusted to match production data. This is the principal reason why streamline-based history matching methods are appealing. Several very different methods for adjusting the reservoir description have been advanced, ranging from mathematically rigorous techniques that alter the properties of each grid-block,6,7,9–13 to heuristic approaches, where average properties in streamline-defined regions are modified in a largely ad-hoc manner.4,14,15 One of the most successful streamline-based history matching methods is Assisted History Matching developed by the Chevron group.1–3 The regions of the reservoir flowing to each production well were identified at some time during the displacement by identifying the grid blocks that streamlines flowing to each production well pass through. Then the permeability, porosity, net-to-gross or heterogeneity of the region was modified in order to improve the match to production data. Adjustments were made independently to each region. The methodology was used to history match several fields containing many hundreds of wells in a fraction of the time (both in terms of engineer's time and computer time) required using more traditional, grid-based methods. The main problem with the method was that the property adjustments were made at the judgment of the reservoir engineer, which makes the method somewhat daunting to a non-expert user. In this paper we extend Assisted History Matching by estimating the modifications to reservoir properties needed to match production data, assuming tracer-like flow. This enables the method to be semi-automatic. We demonstrate the utility of the approach through an application to an Arabian Gulf field with 42 producers and almost 30 years of waterflood production history. Streamline Model In this paper, interactive code is written outside a commercial streamline-based simulator. The simulator we use is 3DSL, a compressible, three-phase black-oil code. The simulation method for incompressible, two-phase flow is described by Batycky et al.17 The extension of the methodology for compressible three-phase flow is outlined briefly in Agarwal and Blunt.16