Design method for well-killing parameters in ultra-deep fractured formations using direct-push method

doi:10.3969/j.issn.1006-6535.2025.03.017

Abstract

Abstract: To address the issue of unreasonable well-killing parameter calculations for the direct-push method in ultra-deep fractured formations, which leads to significant construction safety risks, research, based on seepage theory, wellbore afterflow theory, and gas-liquid two-phase flow theory, has been conducted to investigate the initial distribution state of fluids in the wellbore before well-killing, the pressure variation patterns in the wellbore and formation during well-killing, and the design methods for well-killing fluid density and displacement. Additionally, a dual-gradient well-killing fluid density calculation method and a minimum well-killing fluid displacement calculation method have been established. The study shows that considering overflow circulation, shut-in afterflow, and shut-in slippage before well-killing, and using a drift flow model, it more accurately calculates the height and gas holdup of gas-liquid two-phase flow. The dual-gradient killing fluid density design method proposed with the goal of reservoir protection can reduce the amount of drilling fluid pushed into the formation and significantly lower the risk of reservoir contamination. By integrating the characteristics of bubble slippage under high wellhead backpressure and counter-current gas-liquid flow conditions, the minimum killing fluid displacement for the direct-push method is calculated based on the slippage velocity of small bubbles, which is more practical. The dual-gradient killing fluid density design method and the minimum killing fluid displacement calculation method have been compared and verified with actual well-killing cases and full-scale experiments, with errors all within 20%, indicating that the well-killing parameter design method is scientific and rational. This research method and its results can provide technical references for field engineers when using the direct-push method for well killing.

Key words: well-killing, direct-push method, gas-liquid two-phase flow, bubble slippage, ultra-deep reservoir, fractured formation

CLC Number:

TE257

ZHAO Haijian, LI Dawei, WEI Sizhuang, WANG Xuesong, WU Guang, LI Qingfeng. Design method for well-killing parameters in ultra-deep fractured formations using direct-push method[J]. Special Oil & Gas Reservoirs, 2025, 32(3): 142-149.

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