When applying BOPs in the field, multiple units are typically combined as needed. Generally, an annular preventer is placed at the top, variable bore rams in the middle, and shear rams at the bottom, among others. Various combinations are possible depending on specific field requirements. These assemblies of different BOPs are collectively referred to as a stack.
How to select a Blowout Preventer stack?
The main factors to consider when selecting a hydraulic BOP stack include well classification, formation pressure, casing size, formation fluid type, personnel technical capabilities, technical process requirements, climate impact, transportation conditions, material supply status, and environmental protection requirements. Ultimately, the goal is to achieve balanced drilling, ensure drilling safety, and optimize drilling costs.
① Pressure Rating Selection
The working pressure of a hydraulic BOP stack is determined by the internal pressure resistance of the casing used, the formation fracture pressure at the casing shoe in the open hole, and the anticipated maximum wellhead pressure. However, the primary consideration is the expected maximum wellhead pressure that the BOP stack will need to withstand. Its pressure ratings are available in six categories: 2,000 psi (14 MPa), 3,000 psi (21 MPa), 5,000 psi (35 MPa), 10,000 psi (70 MPa), 15,000 psi (105 MPa), and 20,000 psi (140 MPa).
②Bore Size Selection
Its bore size is determined by the casing size in the well design and must be slightly larger than the outer diameter of the connected casing. BOP bore sizes are available in nine specifications: 7-1/16" (180 mm), 9" (230 mm), 11" (280 mm), 13-5/8" (346 mm), 16-3/4" (426 mm), 18-3/4" (476 mm), 20-3/4" (528 mm), 21-1/4" (540 mm), and 26-3/4" (680 mm). Among these, the most commonly used in the field are 9" (230 mm), 11" (280 mm), 13-5/8" (346 mm), and 21-1/4" (540 mm).
③Stack Configuration Selection
The selection of stack configuration is primarily based on formation pressure, drilling process requirements, drill string structure, and equipment compatibility.
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