The Wainwright field in the Alberta Lloydminster District has produced medium gravity oil (40 cp) under waterflood from roughly 700 inverted 9-spot pattern wells, since the early 1960's. The formation is a moderately consolidated thin Sparky sandstone.
Initially water breakthrough did not show any preferential direction. However in recent years, production performance has been dominated by the effects of fractures between injecting and producing wells. It was apparent that a new waterflood management strategy was needed to optimize ultimate recovery an arrest declining productivity. An investigation of fracture characteristics was done by conducting interwell tracer test, pressure pulse tests and fall off test as well as analyzing production data. Results confirmed very rapid communication between ontrend wells.
From this work, it was found that fractures were orientated on a NE-SW tectonic stress trend and propagation closure was largely dependent on injection rates. There was no definitive fracture pressure. The long tenn solution was identified as field wide conversion from inverted 9-spot to line drive to optimize ultimate recovery take advantage of the fracture system. A short term solution to maintain current levels of production was to reduce high injection rates. By understanding the reservoir and compensating for its high recovery wi11 occur despite fractures and high oil viscosity.
The Wainwright is one of the most mature waterfloods in the Lloydminster District and results from this work might be applicable in the future to similar but younger waterflood projects in the same area.
The Wainwright waterflood is the oldest pressure maintenance project in the Lloydminster heavy oil district (Figures 1 and 2). The pool was discovered in 1923 with the drilling of 13-30-45-6W4; however, field development did not occur until the 1950's. Waterflooding of the Wainwright Sparky reservoir was implemented in the 1960 l s and used inverted nine-spot patterns. Incremental waterflood recovery to date ranges from 25% to 30% of the original oil in place.
Production performance in recent years indicated that fractures between producers and injectors on a northeast/southwest (NE/SW)trend were responsible for declining productivity. The presence of fractures and their behavior has been quantified by geological analysis, analysis of production trends, interwell tracer tests and pressure transient tests. The success of past efforts to increase productivity, such as line drive conversions was also evaluated.
As a result of this work an optimum late-life waterflood operating strategy was developed. Injection rates are currently being reduced to minimize the effects of fractures and field-Wide conversion to line drive is planned in order to optimize ultimate recovery.
Despite an adverse mobility ratio, the Wainwright reservoir responded very favorably to waterflooding. Elxcellent porosity and permeability coupled with good overall pattern coverage are responsible for the high waterflood recovery to date.
The Wainwright oil field produces from the Sparky Formation of the Mannville Group (Figure 3).