Huff-n-puff technology and parameter optimization of large displacement water injection in tight oil reservoir

To address the issue of low natural imbibition recovery in horizontal wells within tight reservoirs and the challenge of replenishing formation energy during extended depletion phases, a strategy involving water injection huff and puff in large displacement horizontal wells was proposed. This approach builds on the fundamental characteristics of reservoirs and the established mechanisms of water injection huff and puff oil production in tight reservoirs. The research focused on the Chang-7 tight reservoir in Ordos Basin, employing a combination of natural and artificial cores. This study explored the range of natural imbibition and the dynamics of water injection and huff and puff across various displacements. Methods like nuclear magnetic resonance were used to analyze the characteristics of microscopic pore production, the impact of displacement on pore productivity, and the effects of soaking time. The findings reveal that with smaller displacements, mainly large pores are utilized for water injection, resulting in minimal engagement of small and medium pores. Conversely, higher water injections significantly enhance the involvement of small and medium-sized pores, thus substantially boosting the overall recovery rate. Additionally, as the simmering time is extended, the oil-water displacement effect increases, enhancing the degree of recovery through water injection huff and puff, though the rate of improvement eventually stabilizes. Numerical simulation was used to optimize the parameters for water injection huff and puff development in fracturing horizontal wells. For Well-A9, the optimal parameters were identified as a daily water injection rate of 900 m³ and a simmering time of 24 days. The field test confirmed the effectiveness of these parameters, with an initial daily oil increase of 2.11 tons, an effective period of 365 days, and a cumulative oil increase of 770 tons.