Abstract

An extensive interwell tracer program was conducted at the Bone Creek Unit between 1984 and 1986. The objectives were to obtain insights into the flow distribution and, to infer clues regarding potential improvements to the waterflood.

Detailed interpretations of tracer returns helped in refining reservoir description in terms of lateral as well as vertical heterogeneities. These additional details were independently verified by a history match of the unit's performance and, were by and large consistent with the cross-section fence diagrams of the pay zone prepared from log and core data.

Based upon the composite knowledge thus obtained, a better understanding of sweep patterns around different injectors resulted.

The tracer program led to certain changes in injection-production patterns. Four infil1 wells were drilled. Several additional infill locations were identified. Many parts of the unit, such as the northwestern portion, experienced poor sweep and poor oil recovery. These were caused, in part, by reservoir heterogeneities. With the improved knowledge of these heterogeneities, appropriate enhanced oil recovery schemes for the unit were explored. Similarly, a better understanding of the performance of the waterflood provided clues to its possible improvement.

Introduction

The Bone Creek/Ins tow pool is a Middle Jurassic, Upper Shaunavon tidal channel deposit located in the Southwestern part of Saskatchewan (Figure 1). It is situated along the Rapdan-Dollard- Gull Lake oilfield trend, an ancient shoreline sequence of sandstone deposits. The pool is approximately eight km long and three km wide, crending in a Northwest-Southeast direction (Figure 2). Relevant pool data are summarized in Table 1.

The pay zone can be divided into two distinct litho-facies, a predominant calcareous sandstone with an average permeability of five millidarcies, and an interbedded quartzose sand with an average permeability of about a hundred millidarcies. Based upon the log and core data, a detailed fence diagram of the pool has been prepared (Figure 3). Because of the variable and discontinuous nature of the quartzose sand members, their continuity from one well to the next is difficult to ascertain. (The percentage of total pay interval belonging to the quartzose members is mapped in Figure 4).

The pool has a low primary recovery (5%) because of the existence of a medium gravity crude oil (914 kg/m3 or, 24 degrees API) discovered initiially at undersaturated conditions. A peripheral waterflood, initiated in 1960 is projected to recover an additional l7% oil-in place (Figures 5 and 6). The. feasibility of any improvement (workovers, altering operation, infill drilling and/or chemical flooding) depends upon a more complete knowledge of the lateral continuity and variability of quartzose sand members. Three members are considered to be the main conduits for accepting injection as well as for contributing the bulk of production.

Saskoil, as the operator of the Bone Creek Unit, conducted an interwell tracer program on the pool between 1984 and 1966. Eleven injection wells received radio-active tracer slugs with the injected water (Table 2. and Figure 7).

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