Pattern Waterflood Development in a Giant, Mature Oil Field: Minas NW Segment Reservoir Characterization, Scale-Up, and Flow Modeling
Authors: Rachmawati S.B. , Sustakoski Rick J. , Whitacre Timothy P. , Goggin David J. , Levy Marjorie , Bernath Alan B. , Anbarci Kemal , Wu Gary 
Published: December 2007

S.B. Rachmawati, Rick J. Sustakoski, Timothy P. Whitacre, P.T. Caltex Pacific Indonesia, David J. Goggin, Marjorie Levy, Alan B. Bernath, Kemal Anbarci, Chevron Petroleum Technology Company, Gary Wu, Texaco Exploration and Production Company

Abstract
Reservoir characterization involves the quantification, integration, reduction, and analysis of geological. petrophysical, seismic, and engineering data. The principal goal of reservoir characterization is to derive a spatial understanding of interval heterogeneity. The result of this analysis can be improved dramatically using 3-D interpretation and analysis techniques. The product of 3D reservoir characterization is a 3D reservoir model which is largely a function of the stratigraphic framework.
Sequence stratigraphy concepts are used to identify and analyze five major depositional sequences in the early Miocene to middle Miocene Sihapas Group in the Northwest Segment of the Minas Field.
The purpose of this paper is to discuss the process and results of a combined, 3-D deterministic and stochastic reservoir modeling procedure. Three-dimensional reservoir modeling results in an improved geologic interpretation while providing an integrated approach and allowing for immediate model updates as a new data is acquired.
The geologic modeling phase of the Minas Northwest Segment project successfully integrated all available interpreted and measured data into a high-resolution, full-field model. Statistical and geostatistical data revealed strong relationships between geologic trends and petrophysical patterns of reservoir heterogeneity. Facies regions combined with the powerful geostatistical methods in G2/GOCAD ++ effectively captured both geologic trends and petrophysical relationships in the final model.
A scaled-up version of the geologic model was used to build streamtube and finite difference simulation models to predict recovery performance for various waterflooding and horizontal well scenarios. An inverted 7-spot pattern waterflood over a high-graded portion of the Northwest Segment was selected as the optimum development approach. The results and recommendations for this pattern waterflood project will be implemented beginning in 1998.
The results derived from 3D scale-up and subsequent flow simulations showed that the geologic model used in this study adequately represents subsurface flow in Minas Northwest Segment.

Introduction
Minas field, located in central Sumatra, is the largest oil field in Southeast Asia (Fig. 1). The Minas field was discovered in 1944, and was placed on production in 1952. To date the field has produced more than 4 billion barrels from an original oil in place of 9 billion barrels.
Minas field is a large (25km × 10km) faulted anticline separated into two major compartments (Minas Main and Minas Northwest) by a right lateral, strike-slip fault. The Northwest Segment represents approximately 20% of the Minas OOIP and is lower structurally than the Main Segment. The primary productive interval is within the Early Miocene Sihapas group. The sandstone reservoirs are at an average depth of 2000 feet subsea. P. 535^