Performance Simulation of the Snipe Lake Beaverhill Lake A Pool A Geologically Complex Reservoir

Abstract

Abstract This paper illustrates the inter-relationship of geology and reservoir engineering in reservoir simulation. A three-phase, three-dimensional, unsteady-state model study was U1ldertaken to resolve the complex pressure and p1'oduction characteristics of the Snipe Lake Beaverhill Lake A Pool and allow 'meaningful predictions of future performance. The study began with a detailed investigation of the geology of the pool to allow the definition and generation of the basic 'model data input. Additional studies of the production, perforation and pressure histories of the wells, taking into account the layering concepts developed in the geological study, helped to indicate broad performance concepts. The history 'matching of the performance, however, proved to be very complex and involved altering the original geological picture of the pool. Introduction THE SNIPE LAKE Beaverhill Lake A Pool, located 160 miles northwest of Edmonton, Alberta (Fig. 1). was discovered in December, 1962 by the drilling of SOBC Snipe 10-21-70-18W5. Development was rapid, with 95 wells completed in the first two years. There are now 108 wells completed within the current pool boundaries, 106 of which are in the Snipe Lake Beaverhill Lake Unit No.1. The pool is approximately 28 miles long (orientated to the northwest) and was less than 5 miles wide in the oil zone at original conditions. There is aquifer downdip to the southwest, although its full extent has not been determined by drilling. The pool is an undersaturated oil accumulation located approximately 8700 feet below surface. The reservoir pressure declined rapidly under primary depletion from the initial pressure of 3815 psig toward the saturation pressure of 1300 psig. The aquifer did not contribute significantly to the reservoir energy. A pilot waterflood was initiated in October, 1964, with fresh-water injection at 4-17-71-18W5, and this was expanded to a full-scale flank waterflood in 1965 with four injectors. Additional injectors have been added since then, until now there are eight fresh water injectors and two produced-water disposal wells. As the waterflood matured, it was apparent that less-sophisticated reservoir evaluation methods were inadequate in resolving the complex pressure and production characteristics of the pool. Fortunately, improved solution routines were making the use of three-dimensional, three-phase, unsteady-state simulators practical for fairly large reservoirs such as Snipe Lake. A comprehensive reservoir model study was thus undertaken to establish revisions in previous theories regarding the waterflood displacement in the pool in order to explain current performance, to predict the results of possible changes in the waterflood scheme and to determine ultimate recovery. The study began with a detailed geological review, which confirmed the complex nature of the pool. A review of the production, perforation and pressure histories of the wells, taking into account the layering concepts developed in the geological study, helped to indicate some broad performance concepts. However, history matching the pool performance revealed that there were significant restrictions in lateral communication between wells which were not apparent from 160-acre well control. Pool Geology The Snipe Lake reservoir is an atoll-like reef in the Swan Hills Formation.