A New Method of Bidirectional Displacement to Enhance Oil Recovery in Fault-block Reservoirs at High Water Cut Stage

Summary This paper focuses on the research of a new method to enhance oil recovery in fault-block reservoirs at high water cut stage. Through three-dimensional water flooding experimental analysis and Nuclear Magnetic Resonance (NMR) analysis, the distribution of remaining oil at high water cut stage in fault block reservoir is clarified from macro and micro aspect. Although the development of reservoirs has stepped into the ultra-high water cut stage, there still has a great potential for development with two kinds of remaining oil. One is located on the top of tectonic structures which is hardly swept by water flooding and the fault barrier increases the recovery difficulty of this kind. The other is the highly dispersive residual oil between wells. The paper investigates the whole vertical structural position and presents a new development mode named bidirectional displacement to extract those two kinds of remaining oil: the top structure is for gas injection while the bottom is for water injection, thereby bidirectionally (upper and lower) compensating formation energy for oil displacement in the middle of the structure. In the higher position, we adjust working system by injecting gas from old wells and then force the gas to migrate to the top to displace oil. During this process, a newly formed artificial gas cap is matched with reservoir scale and displaces oil by gas cap expansion energy when the reservoir pressure declines. At the bottom, we convert oil wells with high water cut into water injection wells with wide well spacing and large displacement to form the artificial edge water flood that can re-aggregate the dispersed remaining oil, achieving efficient development of remaining oil in fault-block reservoirs with bidirectional displacement. In this paper, a typical geological model of fault-block reservoirs is built by numerical simulation, and the factors that influence the development effect are discussed by orthogonal experimental design. We obtain the influence of various development and geological factors on bidirectional displacement, optimize the working system at different developmental stages, establish a corresponding matching relationship between production and injection wells for stable development and form the screening criteria for bidirectional displacement.