深水钻井司钻法压井过程中立管压力和地层受力变化规律

Change law of standpipe pressure and formation stress during well killing by driller method in deepwater drilling

深水钻井地层破裂压力低、钻井液密度窗口窄,溢流时采用司钻法压井,往往未控制溢流却又诱发井漏事故。因此采用深水司钻法压井时地层受力显得尤为重要。考虑节流管汇影响,利用流体动力学,建立了深水钻井司钻法压井立管压力和地层受力计算模型,分析了深水司钻法压井中立管压力和地层压力变化规律,给出了司钻法压井过程中累计泵入长度对应的立管压力、套压、地层受力变化曲线,结合地层破裂压力极限值,确定压井过程中最优压井排量。对于压井排量和钻具组合相同的情况,司钻法压井时,套管鞋越深,套管鞋处地层受力越大;深度大的套管鞋位置出现最大压力时间要早于深度小的套管鞋位置;当天然气柱顶部达到井深某处时,某处地层受力最大;当天然气柱顶部达到井口时,套管压力最大,并且地层受力最大值总是早于套管压力最大值。

During deepwater drilling, the formation breakdown pressure is low and the window of drilling fluid density is narrow, sowhen driller’s method is used to kill a well for well kicks, the result is that the kick is not controlled but lost circulation incident may beinduced. Hence, formation stress seems particularly important when driller’s method is used for well killing in deepwater drilling. Thispaper takes into account the effect of choke manifold, uses fluid dynamics to build a model to calculate standpipe pressure and formationstress when driller’s method is used to kill a well in deepwater drilling. Also, this paper analyzes the varying pattern of standpipe pressureand formation stress during well killing by driller’s method in deepwater drilling, provides the changing curves of standpipe pressure,casing pressure and formation stress relative to cumulative pumping length during well killing by driller’s method, and determines theoptimal kill rate during well killing in conjunction with the limit of formation breakdown pressure. When the kill rate and BHA are thesame, the deeper the casing shoe is, the greater the formation stress is at the casing shoe during well killing by driller’s method. Theoccurrence of maximum pressure at the casing shoe of great depth is earlier than that smaller depth. When the top of gas column reachescertain point in the hole, that point shall be under the maximum pressure. When the top of gas column reaches the wellhead, the casingpressure is the greatest, and the maximum value of formation stress is always earlier than that of casing pressure.