The role of cycling pressure, injection gas composition, soak time and level of primary depletion before initiation of GCEOR and the importance of geology have been measured. Gas-cycling Huff and Puff operations have been analyzed in porous media exhibiting in situ oil permeabilities ranging from 20 to 2000 nD, with fluid densities between 40 and 47 API and gas-oil ratios between 800 and 2750 scf/BBL. The importance of geological properties relative to oil properties in GCEOR design was quantified along with analysis of GCEOR performance in systems exhibiting Peclet numbers changing over two orders of magnitude.
High-permeability fracs and very low permeability matrix have been combined into a novel patent-pending laboratory equipment design whereby large hydrocarbon pore volumes with live reservoir fluids are used. Flow between matrix and fracture(s) is induced by scaling field operations to lab-size experiments and inducing differential pressure gradients between matrix and frac during Huff and Puff cycles. Produced gas, liquid and recombined fluid compositions, as a function of time, are measured along with produced liquid densities. Full reservoir conditions are reproduced and Primary Depletion followed by Huff and Puff GCEOR are evaluated, while changing the design parameters listed above. This work has been performed on diverse oil and rock properties. With this equipment various fluids can be tested in diverse porous media whereby the relative importance of rock properties on GCEOR performance is measured. Moreover, for porous media that exhibit broad pore size distributions, or micro-scale heterogeneity, the efficacy of conformance control agents can be evaluated.
With more than fifty primary depletion tests followed by cyclic Huff and Puff gas injection, insights into GCEOR have been obtained. First-contact miscible gases have been observed to respond very differently as a function of changes in rock properties and reservoir fluid volatility. Performing primary depletion followed by GCEOR with different reservoir fluids but in the same porous media elucidate the importance of rock properties. It was found that appropriate GCEOR design must consider rock quality. Mercury injection capillary pressure data have been measured and are shown to breathe insight into GCEOR performance. For geology that possesses micro-scale heterogeneity water injection was used as a conformance control agent. GCEOR performance is quantified with and without water as a means of conformance control. The effects of cycling pressure, injection gas composition, soak time, level of primary depletion, before GCEOR, and other parameters have been investigated. All GCEOR testing was done in order to quantify the relative benefit compared to primary depletion recovery. This experimental protocol represents a valuable adjunct to using simulation to scale-up from lab to field.