Abstract
Multi-fractured horizontal wells have enabled commercial production from low-permeability (‘tight’) hydrocarbon reservoirs but recoveries remain exceedingly small (< 5–10%). As a result, operators have investigated the use of solvent (gas) injection schemes, such as huff-n-puff (HNP), to improve oil recovery. Previous HNP laboratory approaches, classified primary as ‘flow-through-matrix’ and ‘flow-around-matrix’ typically (1) are not fully representative of field conditions at near-fracture regions and (2) require long test times, even when performed on fractured cores. The objectives of this proof-of-concept study are to (1) design and implement a new experimental procedure that better reproduces HNP schemes in near-fracture regions and (2) use the results, simulated with a compositional lab-calibrated model, to explore the controls on enhanced hydrocarbon recovery in depleted tight oil plays. Performing multiple CO2 and (simplified) lean gas HNP cycles, the integrated experimental and simulation approach proposed herein achieves the ultimate recovery factors in a significantly shorter time frame (25–50%) compared to previous studies. The integrated experimental and computational approach proposed herein is valuable for core-based evaluation of cyclic solvent (CO2, CH4) injection in tight hydrocarbon reservoirs for (1) hydrocarbon recovery and (2) subsurface greenhouse (CO2, CH4) gas disposal/storage applications.
Highlights
Multi-fractured horizontal wells have enabled commercial production from low-permeability (‘tight’) hydrocarbon reservoirs but recoveries remain exceedingly small (< 5–10%)
A summary of the theory behind the HNP process in tight hydrocarbon systems is provided in Supplementary Appendix S1 online
By matching the laboratory results using rigorous fine-scale numerical simulation models, critical parameters that can be used in evaluating fieldscale enhanced oil recovery (EOR) pilots may be obtained
Summary
Multi-fractured horizontal wells have enabled commercial production from low-permeability (‘tight’) hydrocarbon reservoirs but recoveries remain exceedingly small (< 5–10%). Previous HNP laboratory approaches, classified primary as ‘flow-through-matrix’ and ‘flowaround-matrix’ typically (1) are not fully representative of field conditions at near-fracture regions and (2) require long test times, even when performed on fractured cores The objectives of this proof-ofconcept study are to (1) design and implement a new experimental procedure that better reproduces HNP schemes in near-fracture regions and (2) use the results, simulated with a compositional labcalibrated model, to explore the controls on enhanced hydrocarbon recovery in depleted tight oil plays. While seminal works have been conducted to mimic HNP process on fractured c ores[7,8], the fractures were created outside of the coreholder either fully using saw[7] or partially using drilling bits[8] (combined with hydraulic fracturing under stress inside coreholder) These approaches, though more representative, are prone to the creation of stress-induced micro-fractures, in organic-rich shales (the primary target plays for field-scale HNP application). This approach has enabled the measurement of tight rock unpropped/propped fracture permeability/conductivity[23], and fracture c ompressibility[24] under “in-situ” stress and as a function of effective stress
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