Experimental Evaluation of Unconventional Reservoir Sample Properties Using Rate- and Pressure-Transient Analysis Methods

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Ultra-low permeability ("unconventional") reservoirs (URs) that host oil and liquid-rich gas are critical sources of hydrocarbon production in Canada. Multi-fractured horizontal wells (MFHWs) have provided the technology to recover oil, gas and condensate from URs. Early development of these URs has focused on the use of primary recovery (pressure depletion) strategies, but the industry is currently evaluating the potential for enhanced oil recovery (EOR) using cyclic gas (solvent) injection. Optimization of recovery processes using MFHWs, however, requires estimation of key reservoir and hydraulic fracture properties that affect hydrocarbon production and solvent injection. Understanding how to advance reservoir/hydraulic fracture characterization methods is therefore critical for achieving sustainable development of URs through primary and enhanced recovery processes. While reservoir properties may be determined in the laboratory using core samples, the experimental conditions generally do not reproduce the conditions under which MFHWs are produced in the field, and the results are not analyzed in the same way. The usefulness of the laboratory test results for providing critical input models applied to field data are therefore in question. Recently the Clarkson research group developed a new experimental method and analysis procedure to better reproduce conditions under which MFHWs produce in the field. The new revolutionary experimental approach, referred to as `RTAPK', uses the same production data analysis methods as those applied to MFHWs. Analysis of gas production from core plug samples allows the key reservoir properties of permeability and pore volume (and hence porosity) to be determined at in-situ stress conditions. A `proof-of-concept' study demonstrated that core tests could indeed reproduce behaviors observed in the field, and provide key input data faster, and with more confidence, than conventional core testing methods. The success of this proof-of-concept study has inspired the initiation of a new 5-year research program aimed at not only improving laboratory-derived estimates of critical UR properties using the RTAPK method but also evaluating the fundamental controls on fluid flow and storage in unconventional reservoirs. The objectives of this new program are to 1) expand the permeability limits of the RTAPK device to make it more widely applicable to Canadian URs; 2) construct a new RTAPK device for the purpose of determining properties critical to modeling multi-phase (gas, oil, water) flow in URs and; 3) use the resulting RTAPK database to address fundamental questions about the nature of fluid flow in URs. As a result of the further development of this new, innovative laboratory technique, field development planning of Canada's URs using primary and enhanced recovery processes will be improved, leading to more efficient exploitation of these critical hydrocarbon resources.