Performance Evaluation Of The Boundary Lake South Triassic 'H' Pool
Authors: Griswold W. , Ko S.C.M. 
Published: March 2010

A reservoir engineering study of the Boundary Lake South Triassic "H " Pool was conducted to investigate the past performance and to forecast the performance potential of various depletion strategies. A detailed geological and petrophysical review of available data provided the characteristic distribution of reservoir properties. The history match phase of the study confirmed suspicions of fluid communication between the Triassic "H " Pool and a thief zone located above the reservoir. Model forecasts showed that the oil recovery could be increased by approximately 41% over the current development scheme with a program of infill drilling and modification to the injection patterns.

Introduction

The Boundary Lake South Triassic "H " Pool is located approximately 740 km northwest of Edmonton, Alberta. The pool was discovered in 1975 with the drilling of Well 10-10-84-12 W6M. The pool contains a 36 ° API crude with an initial reservoir pressure of 12 740 kPa. Initial estimate of the original oil-in-place (OOIP) was 2.91 × 106m3.

A unit was formed which included the lands located in Sections 10 and 15, west-half of Section 11 and south-half of Section 22, Township 84, Range 12, west of the 6th Meridian. Oil production from the unit area commenced in 1975 under primary depletion. A pressure maintenance scheme by water injection was initiated in 1979. The void age replacement ratio was maintained close to 1.0 until oil production from the non-unit areas began in 1980. At the time of writing this paper, only one of the two non-unit operators is injecting water for pressure maintenance despite waterflood approvals given by the Energy Resources Conservation Board (ERCB) to both non-unit operators in 1985.

As of the beginning of 1983, the unit production was approximately 70 m3 / day and has been experiencing a decline of close to 20% per year. A continuation of this rapid decline would have a serious negative impact on the oil recovery from the unit. As a result, Ultramar Oil and Gas Canada Limited, who is the unit operator, initiated a reservoir study for optimization of waterflood recoverable reserves within the unit.

Geology

The Boundary Lake member of the Triassic Charlie Lake formation comprises two sub-units in the area of the "H " Pool. The lower unit is composed mainly of shales and marl-anhydrite and does not constitute reservoir quality rock. This unit is characterized by four uniformly developed cycles which are easily recognized and was chosen as the structural and stratigraphic datum for reservoir mapping. A type log of the Boundary Lake member is shown in Figure 1.

The upper sub-unit of the Boundary Lake member is the Boundary carbonate. The Boundary carbonate comprises four units, three cyclical units with uniform thickness of two to three metres each and an upper porous zone up to six metres thick as shown in Figure 2. The three lower cyclical units consist of a porous basal carbonate and an upper dense anhydrite or carbonate zone. The porous carbonates of the four cycles, lettered A to D from the basal unit, form the "H " Pool reservoir.