Abstract
An experimental apparatus was developed that provides axial fracture flow and radial matrix flow in the context of differential pressure gradients at full reservoir conditions. Flow within the frac(s) and flow between frac(s) and matrix are operative in the system. The influence of cycling pressure, injection gas composition, soak time and level of primary depletion before initiation of GCEOR have been measured previously with volatile oil systems. To date no direct comparison has been made with rich gas condensate GCEOR performance in the same rock with similar GCEOR design parameters. Primary depletion of a volatile oil in a Montney porous media is compared to primary depletion in the same rock with a rich gas condensate. Pursuant to primary depletion, GCEOR was applied for both the oil and the gas condensate fluid.
A novel experimental design for core-flow testing has permitted the quantification of GCEOR using large lab-scale hydro-carbon pore volumes (HCPV). The unique experimental design allows nano-Darcy media to be tested using a time line comparable to conventional millidarcy media. The porous media tested herein exhibited a reservoir oil permeability of 110 nD at full reservoir conditions. Mechanisms for EOR have been described previously on the basis of this experimental protocol. Due to the large hydrocarbon pore volume of this procedure (130 to 480 ml) measurements of produced gas, liquid and recombined fluid compositions are obtained, as a function of Puff cycle number, as well as produced liquid densities and recovery factors cycle to cycle. These procedures were applied to a volatile oil and a retrograde condensate fluid.
A naturally-fractured porous media was saturated with a dew point fluid exhibiting a condensate-gas ratio of 200 BBL/MMscf. Primary depletion was conducted following a linear pressure depletion corresponding to field-real primary production times scaled to the laboratory experiment. Liquid recovery factor, produced fluid compositions and densities along with frac and matrix pressures were recorded. Pursuant to primary depletion GCEOR was conducted in order to quantify the increased liquid recovery after primary production. The system was then extracted to determine Sor. The porous media was then re-saturated and restored with volatile oil and primary depletion followed by GCEOR. It was observed that liquid recovery factor was better for the gas condensate in this low-permeability porous media. Primary depletion produced higher liquid recovery (C6+) with the gas condensate fluid than with the volatile oil. GCEOR after primary depletion performed similarly. Other insights were obtained and are discussed.
