Model-Based Design of Polymer injection in Viscous Oil Reservoirs Under Bottom Aquifer

Summary 1. Objective and Scope Recently, polymer flooding has been a proven cEOR recovery process in viscous oil reservoirs. Polymer injection concept in reservoirs depleted by horizontal producers and supported by bottom aquifer has gained a considerable attention. In such concept, Polymer injectors are positioned above the aquifer and below the producers. Polymer injection design requires understanding how the time arrival of the oil bank is related to defined control parameters. A Model is introduced to explain how breakthrough time is related to these parameters and hence aid in designing a proper polymer injection. 2. Methodology, Procedure and Process Based on the frontal advance theory in radial geometry, a parametric equation that relates the breakthrough time to the control parameters is introduced and its limitations is discussed. This mathematical model is validated using a reservoir simulator. The grid used is two dimensional where the reservoir is supported by an analytical aquifer. The model is also used to predict the breakthrough time of oil bank in two polymer trials in Oman using real data. 3. Results, Observations and Conclusions The model is derived for an isotropic system and so it should be used whenever the permeability anisotropy is sufficiently close to unity. This result is consistent with the simulation result where the oil bank propagates in ellipses instead of circles when permeability anisotropy <<1. Also, the impact of gravity depends on the gravity number, and it is minimal under practical polymer injection design. The model reveals that the remaining oil saturation, uncontrolled parameter, has a big impact on the oil bank breakthrough time, low remaining oil saturation results in a substantial delay in the breakthrough time besides low oil recovery, a result verified by simulation. For polymer viscosity, the first few centipoises are heavily impacting the arrival time until approximately 20–40cp beyond which the impact starts to be marginal. The model explains the early oil gain arrival in Nimr E6 Trial and the substantial delay in Nimr E157 Trial. The cause of the oil gain delay in Nimr E157 is mainly due to the low remaining oil saturation. 4. Novelty and Additive Information The economic viability of polymer projects is mainly a function of the timing of the oil gain. The model enables engineers to design the optimal control parameters for reservoir with a given remaining oil saturation such that the water cut reversal is observed as early as possible.