Abstract

The Bellshill Lake Pool consists of a thin oil leg overlying a large and active aquifer. The pool produces under essentially 100% water drive with water coning being a major problem. In late 1981, Petro-Canada identified that oil production from the Bellshill Lake Pool could be economically increased from the current 850 m3 /day by a program of infill drilling. Favorable economics for infill drilling were primarily achieved through accelerating oil production.

Single well radial coning models were used to predict well performance. Model results were confirmed by history matching actual well performance using a ‘type curve’ approach.

The study concluded that the number of wells should be substantially increased, reducing the spacing from 9.5 ha/well to 5.5 ha/well. This has led to a phased project to directionally drill an additional 123 artificial lift oil wells. To date, 39 directionally drilled wells and related expansion to the production facilities have been completed.

This paper describes the approach used in the reservoir study, the justification used for directional drilling and the drilling procedure.

Introduction

The Bellshill Lake Field is located approximatp.ly 150 kilometers southeast of Edmonton, as shown in Figure 1. The original discovery well, McLennan 06-32-41-12 W4M, was completed in January, 1956 as an oil well in the Ellerslie Blairmore formation.

Following the discovery, an active development drilling program on 16 ha (40 acre) spacing was carried out through 1959. Additional infill drilling since that time has resulted in approximately 200 wells being drilled to date. Most of the pool was unitized in 1970.

The unit production in 1982 averaged 805 m3 /day of oil at a water cut of 87% and a GOR of 90 m /m3. Cumulative oil production to January 1, 1983 was 5.8 106 m3or 20.5% of the original oil-in-place. Figure 2 shows the recent production history.

RESERVOIR DESCRIPTION

The Basal Quartz sandstone reservoir originally contained 12 m of 27 ° API, 9.2 centipoise oil. Figure 3 shows the original net oil pay in the pool. The oil is underlain by a very active aquifer which has maintained pressure within 250 kPa of the initial pressure of 6 481 kPa. The active aquifer and unfavorable mobility ratio of water to oil have resulted in severe water coning.

The formation is a fine to medium grained semi-consolidated sand with occasion;]l thin shale streaks. Sand quality generally improves with depth achieving 30% porosity and several darcies permeability.

Table I summarizes the reservoir properties.

The original oil water contact dipped northwesterly, apparently as a consequence of the active aquifer drive, varying by 7 m over the length of the pool. The position of the contact is now highly distorted due to coning around the producing wells.

RESERVOTR STUDY

It was obvious from the rapid increase in water-ail-ratio that recovery of oil could only be achieved by producing at very high water cuts for an extended period of time. Therefore, a numerical coning model study was undertaken to predict.

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