Design Guidelines for Limited-Entry Liner Completions in Heterogeneous Reservoirs

Abstract The limited-entry liner is a completion technique that enables efficient acid stimulation thanks to the space-out of a number of small, pre-drilled orifice holes. In this work, general design guidelines are developed for formations with variation in reservoir pressure, permeability and wellbore inclination based on detailed wellbore simulations. The impact of well trajectory is investigated by varying the inclination of the horizontal section for different combinations of injection fluids and reservoir fluids. The key factor impacting the outflow profile is the density difference between the two fluids as well as the injection rate. We show an example where a uniform flow profile during acid bull-heading does not necessarily translate into a uniform outflux distribution during CO2 injection. A two-degree downward sloping is enough to prevent CO2 from reaching the toe of the well unless the injection rate exceeds a certain threshold. The changeover from water to CO2 in a slanted WAG well would therefore require special attention in terms of hole spacing design. The large number of sensitivity runs has shed more light on the best strategy for stimulating intervals that have either higher or lower permeability than the other intervals, assuming that swellable packers are available to isolate each interval. Permeability variation has a different impact on the liner design in low-permeable formations compared to high-permeability rocks. When the average permeability is below 2-3mD with one or more intervals below 1mD, a uniform flow profile would require choking of the 2-3mD intervals, which is not desirable. Furthermore, the pump rate would be constrained by the fracturing pressure in the low-perm intervals. Instead, it is more appropriate to eliminate any choking and accept that some intervals take more acid than others, as long as the low-perm segments receive a certain minimum threshold acid coverage at a given minimum jet velocity, which depends on the acid-rock system.