Recovery Strategies and Flow Modeling in Fractured Carbonates with High Permeability Conduits

Yajie Cheng


This presentation introduces thermal recovery strategies in a validated heterogeneous carbonate model,  solvent-aided process in the Grosmont carbonate and multi-physical flow in karstified carbonates. From the thermal recovery strategies in a validated heterogeneous carbonate model, we can see that gracture spacing, rock compressibility, rock heat capability and a rock-in-fracture fraction have relatively large influences on the production and BHP. Also, fracture properties are more sensitive in a higher permeability reservoir. A vertical well CSS has severe steam overriding and limited sweep regions whereas SAGD performance in carbonates varies dramatically near severe karst regions. The improved hybrid SAGD in a staggered pattern promotes sweep efficiency and retains more heat. High permeability conduits accelerate thermal communication between wells. The optimal cycle numbers switching to a continuous period are the time that cyclic production become declined. A shorter cycle initially and a longer cycle later may be economic and effective for the whole hybrid SAGD operation. From the solvent-aided process in the Grosmont carbonate, we can see that initial solution gas impedes heat transferring and solvent mixing, but it prevents steam channeling to some extent. Various drainage mechanisms combine to achieve a 12% more bitumen recovery factor using pentane with less steam injection than the Base-SAGD. Bitumen recovery is not proportional to a solvent volume fraction. Also, a lighter solvent like C5 is thought to be more suitable in an actual Grosmont carbonate. From the multi-physical flow in karstified carbonates, we can see that the Brinkman-Stokes model can be employed to describe a multi-physical flow in karstified carbonates with large fractures and porous media. Estimating an accurate value of fracture permeability has small influence on production. A permeability ratio K_f/K_m ≈10^5 is found below which the Brinkman-Stokes model is preferable to describe the multi-physical flow compared with the conventional Darcy-Darcy model. Different grid resolutions around fractures also change a production rate.