Insights On Reservoir Heterogeneities And Performance Of Waterflood At The Bone Creek Unit Obtained From Interwell Tracer Interpretations
Authors: Singhal A.K. , Nieuwenburg G. , Dagdick L. , Roach N. 
Published: March 2010

An extensive interwell tracer program was conducted at file 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 sectional 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 new wells were drilled. Several additional infill locations were identified many parts of the unit, such as the north-western portion experienced poor sweep and poor oil recovery. These were caused, in part, by reservoir heterogeneities. As a follow-up to the insights on heterogeneities as revealed during this study, 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

Geology

The Bone Creek/Instow pool is a Middle Jurassic, Upper Shaunavon tidal channel deposit in the southwestern part or Saskatchewan (Fig. 1). It is situated along the Rapdan-Dollard-Gull Lake oilfield trend, an ancient shoreline sequence of sandstone deposits). The pool is approximately 8 km long and 3 km wide trending in a northwest-southeast direction (Fig. 2). l\ stratigraphic cros section is shown in Figure 3. Other relevant pool data are summarized in Table 1.

The pay zone can be divided into two disrinct lithofacies; a predominant calcareous sandstone with an average permeability of 5 millidarcies, and an interbedded quartzose sand with an average permeability or about 100 millidarcies(1). Because of this large contrast, quartzose members constitute the main productive units.

Based upon the log and core data, a detailed fence diagram of the pool was prepared, a portion or which is shown in figure 4. The extreme variability in thicknesses and continuity of the quartzose members can be seen from this figure. In particular, it may be noted that well 5–26 contains no quartzose members although, the surrounding wells contain varying amounts of the quartzose pay. 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 5. By examining Figures 2 and 5 together, it can be seen that about a quarter of the pay zone consists of the quartzose members.

Production History

The pool was discovered in 1954 and developed on a 32 ha spacing. Due to very low permeability of the calcarcous zone, many wells were fractured during completion. Peak production or 350 m3/d was achieved in December 1956. However, decline rates or 20% per year were seen.