| Popis: |
Exact solutions are presented for the circulating temperature profiles in an arbitrarily complex deepwater HP/HT well. The methodology is based on coupling multiple segments via interface temperature matching conditions, and can handle deviated wells curvature, tortuosity, variable lithology and multiple geothermal gradients. Frictional heating both at the drillbit and due to the Negative Joule-Thomson Effect are included by coupling the flow hydraulics to heat transfer. These have been largely neglected in previous studies Both forward and reverse circulation scenarios are considered, as are temperature changes across the drill bit at the hole TD. Heat transfer to the ambient and atmosphere above the mudline through the riser are also included in the formulation. Variable fluid thermophysical properties are accommodated by an iterative application of the derived exact solutions. Non-Newtonian flow effects based on the rheological parameters of the fluid are considered in both the hydraulics and heat transfer aspects of the circulating flow. The method is numerically stable, robust and capable of handling virtually all scenarios in conventional overbalanced drilling. Despite the complexity of the underlying problem, the solution can be implemented in a programmable spreadsheet. The results show that the circulation rate and inlet temperature have the greatest influence on the circulating temperatures while ROP has a minimal impact because of the pseudo-steady state heat transfer conditions. The key finding is that ignoring frictional effects can result in substantial under-prediction of circulating bottomhole temperatures at higher flow rates, particularly for synthetic/oil-based drilling fluids. |
