Toe-To-Heel Waterflooding: Field Scale Numerical Simulation Study

Abstract Application of conventional waterflooding to heavy oil reservoirs is plagued with problems. The unfavorable water/oil mobility ratio often aggravates the negative effects of water channeling and gravity segregation. In order to overcome these difficulties, a novel process, Toe-To-Heel Waterflooding (TTHW) has been developed. The TTHW process utilizes a horizontal producer (HP) and a vertical injector (VI). The horizontal leg of the HP is located at the top of the formation and the VI is placed near the toe of the horizontal producer, in a staggered line drive configuration. The basic idea is to take advantage of the gravity segregation. When water is injected, an early water break-through from VI to the toe of the HP significantly reduces the pressure drop between VI and HP, making gravity an important factor. By gravity segregation, injected water goes to the bottom of the formation, and gradually pushes the oil upward toward the HP at the top of the formation. The current paper is the third in a series of technical articles presenting laboratory and simulation work on TTHW in view of field applications. Results from laboratory tests demonstrated that the TTHW process was a more effective displacement process, compared to the conventional waterflooding with vertical producers and injectors. A 3-D numerical simulation study of the TTHW process at field scale using Computer Modeling Group’s (CMG) STARS reservoir simulator was conducted. Based on an inverted nine-spot pattern, the performance of the TTHW process is compared to that of conventional waterflooding under various reservoir and operational conditions. The simulation results suggest that the best conditions for TTHW to give better performance over conventional vertical-to-vertical waterflooding are large pay thickness and high permeability. In this type of reservoirs, the water segregation due to gravity is significant, making TTHW more effective. In addition, for lower permeability (< 500 md) and higher oil viscosity (> 500 mPa-s) reservoirs, conventional water flooding is almost not applicable due to very low water injectivity. Using TTHW, the injectivity can be significantly improved, resulting in a significant increment on oil recovery. TTHW process extends waterflooding technique to reservoirs that cannot be water flooded by conventional method.