Flood Management: Solving Conformance or Sweep Efficiency Problems: Part 1

Abstract

_ Since the advent of secondary recovery mechanisms, waterflooding or gas displacement, the oil industry has suffered from a variety of problems that yield inefficient displacement of hydrocarbon fluids during flooding. The industry has also suffered from a very low success rate at correcting these poor sweep efficiency problems. The first three articles in this series are designed to enhance our ability to identify, characterize, solve, and evaluate performance of solutions applied to conformance or sweep efficiency problems. This process structure will allow us to discuss key elements that should generate a higher success rate in solving conformance problems. Part 1 of this series focuses on candidate selection and problem clarification or problem understanding which are the first two elements of Fig 1. Overview The process wheel shown in Fig. 1 is used to identify the steps most production engineering companies take as they work through their conformance or sweep efficiency problems. This provides a basis by which we can discuss the various elements of solving these problems. The companies I have worked for chose to call this “conformance engineering.” Let’s define conformance engineering as: The process of utilizing reservoir and wellbore information to understand the flood performance and then use that understanding to adjust aspects of the flood which results in improved oil recovery. That is the working definition this series of articles will use for conformance engineering. I think we can all agree that this includes a large variety of sweep efficiency problems. These range from deep reservoir displacement fluid control issues to near-wellbore control issues and every combination of these elements. This includes issues for controlling displacing fluids at the injector or the producer. We can also use this to understand and characterize human-induced floods vs. natural processes. Strong water aquifer drives have the same displacement mechanisms as waterflooding. They have significant differences to elements like the pressure source, which is broad for aquifer drive and a very specific point source of pressure for pattern floods. In addition, a strong aquifer drive utilizes gravity segregation to enhance the efficiency of the drive where a pattern waterflood can suffer from gravity underrun. This is one of the reasons a peripheral waterflood can be a very effective secondary recovery process. We also consider fields where natural gas cap expansion drives oil displacement. In some fields, the gas cap is supported by gas reinjection. Prudhoe Bay is a prime example where there is no market for natural gas, so gas reinjection into the gas cap and gas cap expansion becomes a strong recovery mechanism for this field. For the sake of this JPT article series we will consider any flood process whether natural or induced to be part of flood management basics.