Abstract
Fast production decline in Saskatchewan's tight oil assets has left behind billions of barrels of oil. In the past few years, waterflooding has been utilized to reduce the production decline rate to some extent, however, further optimization in waterflood performance is desired by operators. In this paper, we present our methodology to enhance waterflooding in Saskatchewan's Bakken field, reducing the rate of production decline. This methodology relies upon surfactant-based production enhancement formulations specifically designed to boost waterflood performance. Laboratory experiments and field design are presented to support the assertion that waterflood performance can be enhanced. This approach is one of the earliest of its kind that systematically utilizes the surfactant to enhance water floods in Saskatchewan's assets.
In this paper, we cover the laboratory formulations, fluid-fluid and rock-fluid tests, and the pilot design process. Laboratory work includes formulation development and screening through stability, interfacial tension (IFT) measurement, emulsion tendency and imbibition tests to evaluate the rate of oil recovery against current waterflood. A correlation between IFT and oil recovery was observed and is also discussed. Using a spontaneous imbibition test and our optimized formulations resulted in an additional 35% of original oil in place (OOIP) recovery at 1000 ppm concentration compared to the 20% OOIP oil recovery when placed in brine only. As a result, wettability alteration and IFT reduction were identified as mechanisms that are effective at enhancing incremental oil recovery beyond the secondary brine mode.
After promising laboratory observations, a pilot design area was selected in Saskatchewan. Through a detailed analysis of well communications, breakthroughs, cumulative injection and production volumes, numerical simulation, and economics, a slug size of surfactant solution was proposed. It was identified that our designed treatment could be ineffective to some well patterns with strong frac communications and very short breakthrough times; however, a conformance treatment has been designed for these specific areas. The preliminary laboratory work and design work support the requirements to proceed to the next step of a pilot.
Successful results using this approach demonstrate the potential to increase the amount of recoverable resources in tight oil plays under waterflood.
