The Y basin in the South China Sea has 15 trillion m³ of natural gas and represents typical ultra high-pressure high-temperature (ultra-HPHT) subsurface conditions, with the maximum bottomhole pressure (BHP) of 142 MPa (equivalent density = 2.38 sg), the highest bottomhole temperature (BHT) of 249°C at a depth of 5638 m, and an extremely narrow drilling mud density window. Therefore, there are several kinds of technical challenges during drilling operations. In recent years, managed pressure drilling (MPD) has been successfully applied in the basin with reduction of risks and well cost. Presented research focuses on a successful field case study of MPD in the Y basin.

The case study consisted of two parts: MPD operational designs and MPD operational procedures. MPD operational designs included two steps: the precise calculation of drilling fluid equivalent circulating density (ECD) and the optimization of operational parameters. Four models were used in calculating drilling fluid ECD: wellbore heat transfer model, drilling fluid equivalent static density (ESD) model, drilling fluid rheological property model, and incorporating the effects of cuttings in the pressure loss model. The second step included two key operational parameters: mud weight (MW) and surface backpressure (SBP). MPD operational procedures were performed in three steps: roles and responsibilities of key personnel during MPD operations, wellsite training program and emergency procedures. Emergency procedures included unexpected drilling events, downhole equipment failures, and surface equipment failures.

Taking X-1 Well as an example from the field case study, the following important observations were made. First, the MPD equipment was installed after remodeling of the drilling platform, installation of the wellhead assembly, and pressure testing of the MPD equipment. Next, the MW was set to 2.15 sg and the SBP was maintained at 525 psi while drilling the 8³/₈ in. hole section on the basis of the operational design. In addition, the possible risks and corresponding preventive measures were taken into account and the MPD casedhole fingerprinting exercises were carried out. Finally, the MPD was successfully applied to X gas field featuring offshore ultra-HPHT. In addition, the dynamic formation integrity test (DFIT) and stripping out of hole with SBP were conducted. The well was successfully drilled in the narrow drilling mud density window of 0.05 sg without incidents and a sharp drop in the nonproductive time (NPT) was observed. Also, the casing structure was optimized from 7 to 5 strings with a significant reduction in the well cost and drilling time.

南海Y盆地的天然气为15万亿立方米³，代表典型的超高压高温（ultra-HPHT）地下条件，最大井底压力（BHP）为142 MPa（等效密度= 2.38） sg），在5638 m深度处的最高井底温度（BHT）249°C和极其狭窄的钻井泥浆密度窗口。因此，在钻井作业期间存在多种技术挑战。近年来，有管理的压力钻井（MPD）已在盆地中成功应用，从而降低了风险并降低了钻井成本。当前的研究重点是Y盆地MPD成功的现场案例研究。

案例研究包括两个部分：MPD操作设计和MPD操作程序。MPD的运行设计包括两个步骤：精确计算钻井液等效循环密度（ECD）和优化运行参数。四种模型用于计算钻井液ECD：井筒传热模型，钻井液等效静密度（ESD）模型，钻井液流变特性模型，以及将钻屑的影响纳入压力损失模型中。第二步包括两个关键操作参数：泥浆重量（MW）和表面反压（SBP）。MPD操作程序分三个步骤执行：MPD操作过程中关键人员的角色和职责，井场培训计划和应急程序。紧急程序包括意外的钻探事件，

以X-1井为例，从现场案例研究中得出以下重要结论。首先，在对钻井平台进行改造，安装井口组件以及对MPD设备进行压力测试之后，再安装MPD设备。接着，将MW设定为2.15 sg和SBP保持在525磅，而钻8 ³ / ₈in。孔部分根据操作设计。此外，考虑了可能的风险和相应的预防措施，并进行了MPD套管井指纹研究。最终，MPD成功地应用于以海上超高温高压为特征的X气田。此外，还进行了动态地层完整性测试（DFIT），并使用SBP进行了井眼剥离。该井在0.05 sg的狭窄钻井泥浆密度窗口中成功钻探，没有发生事故，并且观察到非生产时间（NPT）急剧下降。而且，套管结构从7根柱子优化到5根柱子，显着减少了井成本和钻井时间。