Following uncontrolled discharge during loss of well control events, fracture initiation occurring during the post-blowout capping stage can lead to reservoir fluids broaching to the seafloor. A classic example is Union Oil’s 1969 oil spill in Santa Barbara Channel, where fracture initiation at various locations caused thousands of gallons per hour to broach onto the ocean floor over a month before it could be controlled (Mullineaux 1970; Easton 1972). Disasters such as these could be prevented if the effects of the post-blowout loss of well control stages (uncontrolled discharge and capping) are incorporated into the shut-in procedures, and the wellbore architectures are modified accordingly.

In this study, analytical models are used to simulate the loads on the wellbore during the different stages of loss of control. Capping pressure buildup during the shut-in is modeled to indicate fracture initiation points during the capping stage. Using these models, the critical capping pressure for a well is determined, and subsequent critical discharge flow rates are calculated. Fracture initiation would occur if the actual discharge flow rate is below the calculated critical discharge flow rate. A hypothetical case study using typical deepwater Gulf of Mexico (GOM) parameters is performed demonstrating the likelihood of fracture initiation during different discharge flow rates, discharge periods, and capping stack shut-in methods (single-step/“abrupt” or multistep/“incremental”). An abrupt shut-in for this case study leads to fracture initiation at approximately 8 hours after shut-in, while a five-step incremental shut-in is shown to prevent any fracture initiation during the 48 hours after the beginning of the shut-in. Reservoir depletion through longer discharge periods or higher discharge flow rates, despite the adverse environmental effect, can delay or even prevent fracture initiations during post-blowout capping.

The ability to model these fracture failures enhances the understanding of wellbore integrity problems induced during loss of control situations and helps create workflows for predicting possible broaching scenarios during the post-blowout capping stage. Dimensionless plots are used to present fracture initiation for different cases—this is useful for drilling and wellbore integrity engineers for making contingency plans for dealing with loss of well control situations.

在失去控制井事件的过程中排放失控之后，在井喷后封盖阶段发生的裂缝萌生可能导致储层流体被拉到海底。一个典型的例子是联合石油公司（Union Oil）1969年在圣塔芭芭拉海峡发生的漏油事件，在该位置发生裂缝后，一个月内每小时有数千加仑的油每小时被拉到海床，然后才得以控制（Mullineaux 1970； Easton 1972）。如果将井控阶段井喷后损失（不受控的排放和封顶）的影响纳入关闭程序中，并相应地修改井眼结构，则可以避免此类灾难。

在这项研究中，分析模型用于模拟失去控制的不同阶段中井筒上的载荷。对闭井过程中的封顶压力累积进行建模，以指示封顶阶段的裂缝起始点。使用这些模型，可以确定油井的临界封盖压力，并计算出随后的临界排放流量。如果实际排放流量低于计算的临界排放流量，则会发生断裂。进行了一个使用典型深水墨西哥湾（GOM）参数的假设案例研究，表明了在不同的排放流量，排放时间和封盖堆垛关闭方法（单步/“突变”或多步/“增加的”）。对于本案例研究，突然关闭会导致在关闭后约8小时内开始骨折，而显示五步增量关闭会防止在开始关闭后的48小时内发生任何骨折开始。尽管有不利的环境影响，但较长的排放时间或较高的排放流量会导致储层枯竭，但可能会延迟甚至阻止井喷后封顶过程中裂缝的爆发。

对这些裂缝故障进行建模的能力增强了对失去控制情况期间引发的井眼完整性问题的了解，并有助于创建工作流以预测井喷后封盖阶段可能出现的拉削情况。无因次图用于表示不同情况下的压裂起始点，这对于钻井和井眼完整性工程师制定应急计划以应对井控情况的损失很有用。