Stream Channel Concept Applied to Waterflood Performance Calculations For Multiwell, Multizone, Three-Component Cases

Abstract

The system of programs outlined here should enable the engineer to conduct economic feasibility studies for water injection projects containing irregularly located wells. The flexibility of this technique will permit the selection of the optimum pattern and well density for multiple-zone reservoirs and should be particularly, useful for small and medium-sized projects. projects. Introduction In practice, potential water injection projects frequently contain wells on asymmetrical spacing and hence do not lend themselves to a satisfactory analysis by many performance estimate methods. Also, fields that have been developed on an even spacing often contain irregular edge locations or geologic features that complicate application of standard waterflood prediction methods. When such problems are prediction methods. When such problems are encountered, the technique generally employed is to approximate field conditions by one or more simplified geometric forms representing average conditions. This approach is often time-consuming and may produce unreliable results, depending on the degree of approximation. Numeric simulators provide a more sophisticated analysis; however, the engineering and computer time required to model the reservoir and to match past performance generally restricts their use to larger projects. As a means of computing shape factors for any well spacing and flood pattern, Higgins et al. described a technique whereby a potentiometric model was used to define the streamline system. The volumes of channels and the shape factors were determined from potentiometric model streamline data. potentiometric model streamline data. The technique we propose here utilizes information on streamline positions similar to that obtained from the more time-consuming potentiometric model studies. Expansion of the Higgins-Leighton waterflood performance program to asymmetrical conditions performance program to asymmetrical conditions required the addition of a program to generate a streamline network and another to produce shape factors from the streamline-defined channels. The combined programs provide a rapid means of estimating programs provide a rapid means of estimating performance of small- to intermediate-sized waterfloods performance of small- to intermediate-sized waterfloods or pressure maintenance projects. Discussion of Technique The expanded waterflood performance program consists of adding programs for streamlines, related shape factors, and well-zone-field combinations to the original Higgins-Leighton method. First, a streamline network is developed that provides both the sides and axes of channels connecting injectors to producers. The areas of the channels are integrated and divided into 40 equal parts for computation of the shape factors. Since ideal conditions are assumed, the shape factors may be used for overlying or underlying zones, provided the ratios of flow capacities are the same provided the ratios of flow capacities are the same between wells. Gas and oil are then displaced from channels of the model, thus providing an estimate of water injection and oil, water, and gas production. In the final operation, the injector-producer channel performance is combined for a well-zone-field estimate performance is combined for a well-zone-field estimate of water injection and produced fluids. The application may be visualized from the injector-producer pair illustrated on Fig. 1. P. 373