Smart Waterflooding Tight Fractured Reservoirs Using Inflow Control Valves

Abstract

Abstract Pressure cycling is a technique that makes use of smart well technology to optimize waterfloods in tight fractured reservoirs with horizontal wells. It is an adaptation of another technique known as pressure pulsing, which involves cycling an entire injection well. In pressure cycling, selected intervals of the well are cycled rather than the entire well. By controlling water injection across these intervals, it is possible to prevent water shortcutting between producer-injector pairs due to fractures, thus greatly improving the probability of success of the waterflood. During pressure cycling, an optimized balance is reached between periods of injection into the fractured zone and periods of injection into only the matrix. This optimized balance results in an increase in cumulative oil production over other solutions like chemical or mechanical fracture shut-off in tight fractured reservoirs. In pressure cycling, inflow control valves (isolated with packers) are placed in a horizontal injector across from fractured zones. The horizontal producer belonging to the well pair is left as it is, with a conventional completion. During waterflooding operations, water cut is measured in the producer. Based on the water cut measurement in the producer, valves in the injector are either opened or closed, taking care to maximize oil production, minimize water production, and maintain reservoir pressure. The cycling technique repeats over the years, though progressively becoming less efficient as the matrix around the fractures becomes more saturated with water. In this study, pressure cycling was tested via reservoir simulation on a 2D generic model. The model included a tight homogenous matrix (5 mD) and three thin explicit fractures (width of 1 cm each). Both the production and injection wells were completed in the oil leg of the reservoir. The fractures were assumed to be extensive enough to span the two horizontal wells, but not extensive enough to intersect the aquifer. The simulation results from the model help identify two factors which greatly influence the pressure cycling technique. These are: (1) the fractured zone injectivity, and (2) the matrix injectivity. In fact, the ratio of the fractured zone to matrix injectivity is the key in determining the applicability of pressure cycling. It can be concluded that: When the injectivity ratio increases, i.e. for lower matrix injectivities and/or higher fracture density, the scope for pressure cycling increases significantly.