Experimental Evaluation on Feasibility of Water Huff-N-Puff Processes in a Naturally Fractured Oil Reservoir With Low Permeability

Abstract In this study, a pragmatic and integrated technique has been developed to experimentally evaluate the feasibility of water huff-n-puff processes in a naturally fractured oil reservoir with low permeability. Firstly, the pore-throat structures of core samples collected from a naturally fractured oil reservoir with low permeability were measured. Subsequently, water huff-n-puff experiments integrated with the nuclear magnetic resonance (NMR) measurement were conducted. By analyzing the oil-water production profiles, oil recovery factor, residual oil distribution and saturation variation at various stages, production performance and microscopic oil-sweeping characteristics of core samples with and without natural fractures were evaluated and analyzed. Compared to core samples without natural fractures, the oil recovery factor of core samples with natural fractures increases from 28.38% to 35.63%. The oil in pores connected by smaller throats is clearly displaced through imbibition, the production characteristics are primarily governed by the displacement from natural fractures and larger throats, and thus implementing water huff-n-puff techniques in naturally fractured oil reservoirs with low permeability has proven to be both effective and feasible. Natural fractures effectively reduce the oil-water flow resistance at the injection and production stage, resulting in an increase in the oil-sweeping range and enhancing imbibition through an increased contact area of oil-water-rock as well. The oil recovery factor of a single cycle decreases gradually with the increase of cycles. The findings presented herein provide a basis for the assessment and optimization of water huff-n-puff operations in naturally fractured oil reservoirs with low permeability.