Perforation Optimisation for Long Horizontal Wells in Heterogeneous Reservoirs

Perforated completion is one of the most common completion methods for horizontal wells and perforation density optimisation plays a crucial role in alleviating water cut of wells in water-driven reservoir. Unscientific perforation scheme may leads to ununiform production influx profile and premature water breakthrough which will shorten production period, reduce production and lower ultimate recovery. Numerous theoretical models on perforation distribution design have been proposed. However, with horizontal wellbore becoming longer and longer and heterogeneous reservoirs growing into mature (or high water cut) period, perforation density optimisation based on reservoir description becomes urgent for water breakthrough retardation as well as water crest blocking. By now, the published models haven’t genuinely met this requirement. A coupled numerical reservoir/wellbore model for horizontal wells is presented taking reservoir fluid flow in porous media, near wellbore inflow and wellbore conduit flow into consideration based on reservoir numerical simulation and wellbore dynamics, hence a perforation density optimisation method following influx-control theory is proposed. Sensitivity analysis on perforation distribution as well as influx profile of three effects including horizontal length, pressure drawdown in wellbore, and permeability heterogeneity carried out. Results show that perforation density optimisation is a compromised result of the above three parameters; the heel (toe) section filtration difference will dominate perforation optimisation when the horizontal length is short, and on the other hand, pressure drawdown will have significant effect on perforation especially when the horizontal well has fully penetrated the reservoir or the pressure drawdown is big enough; to obtain homogenized production influx profile, perforation density should be lower in high-permeability section than that in low-permeability stripe. The research proposes an improved model for perforation design and optimisation of long horizontal wells. It also provides a basis for other completion types like inflow control device and intelligent completion.