Solvent Tracers And The Judy Creek Hydrocarbon Miscible Flood
Authors: Wood Kelvin , Lai Francis , Woodford Ray , Taylor Harold 
Published: March 2010

Radioisotopic liquid hydrocarbons have been successfully used as solvent tracers for the Judy Creek Beaverhill Lake "'A" Pool horizontal hydrocarbon miscible flood. Tritiated toluene and tritiated normal alkanes from pentane to octane were selectively injected as tracers into miscible flood patterns during solvent injection cycles. Subsequent tracer production at wells surrounding the miscible injectors provided a means to confirm each pattern's contribution to tertiary oil response at those wells. Communication with pattern injectors was an important factor to consider when solvent sweep was estimated and candidate areas were evaluated for pattern reconfiguration. Tracing program results were used to identify solvent migration from pattern areas. Field engineers used the information on flow distributions to advantage when they made changes to injection and production rates in order to improve pattern balancing. This paper includes a description of a new analysis technique which uses fractional distillation and gas chromatography to determine tracer activities in produced oil samples. Details of tracer injection and sampling strategies are also discussed.

Introduction

The Judy Creek Beaverhill Lake (BHL) "A" Pool is located 240 Ian northwest of Edmonton. The pool is an atoll-like reefal limestone complex of upper Devonian age. The reef has an areal extent of approximately 115 km2 and is up to 70 m thick. Together, the reef and platform limestones comprise the Swan Hills Formation of me Beaverhill Lake Group. Figure 1 shows a structural cross section of the reef along a line drawn from the northeast to the southwest. It is divided into live growth cycles. The uppermost production interval is the R-5, which is generally continuous with 90% of its porosity greater than 6%. This interval contained 41%of the pool's original-oil-in-place (OOIP). The remaining four cyclescan be grouped into interior and margin areas based on facies, with 32% of the pool's OOIP in the highly continuous reef margin. The best reservoir is found in the forereef, to the northeast. In the stratified reef interior, porosity is discontinuous and occurs as patches and lenses(1).

The pool was discovered in 1959. Water injection commenced in 1964 into down-dip pool edge locations to help maintain reservoirressure. It was found that the injected water followed the highly permeable reef rim; the relatively impermeable interior facies presented barriers to fluid movement to the reefs interior. The severe pressure gradients that developed provided convincing evidence of the reservoir's complexity. In 1974 a pattern waterflood was initiated and water injection into the peripheral injectors was reduced. These actions gradually corrected the pressure imbalance across the reservoir. Approval for a horizontal hydrocarbon miscible flood was received from Alberta's Energy Resources Conservation Board in 1983. In Mar 1985, solvent injection commenced into four patterns of what was then planned to ultimately be a 56-pattern commercial project. Figure 2 shows the miscible flood patterns in relationship o the project boundaries as of February 1990.

Hydrocarbon miscible flood surveillance included an extensive solvent radioisotope tracing program. As described by Jonasson(2), the program's objectives were to provide information on continuity, directional now trends and solvent flow beyond miscible patternboundaries.