Among the challenges facing an operator while drilling offshore in the Middle East are the 16-in. sections of wells where highrisk of losses and torque and drag limitations force the operator to be extremely conservative during the planning stage. Operator objectives for this particular interval normally call for mitigating any high-potential incidents, which is driven by the past experiences as well as decades of old best practices. The approach used in the past has been to drill with a positive-displacement mud motor and weighted mud until losses are experienced, and then switch to mudcap drilling to maintain hydrostatic while drilling. The positive displacement mud motor efficiency is excellent in lower inclination wells but deteriorates once the inclination exceeds 30n, leading to significantly lower penetration rates and extending the openhole wellbore exposure time. This prolonged openhole time exposes the bottomhole assembly and wellbore to the same risks the operator has always attempted to avoid.
A service provider evaluated the drilling method with the objective of reducing the drilling time and drilling risks. Drawing from offset well experiences and the conditions of successful operations, a motorized rotary steerable system (RSS) was proposed to the operator. Time and cost analysis were performed, showing that improved hydraulics and drilling dynamics would result in significanttime savings and should be compounded as the 16-in sections are drilled in batches of up to seven wells.
The operator implemented the recommended BHA and parameter design for the remaining seven wells, resulting in up to a 120% increase in the average rate of penetration by the motorized RSS over conventional positive displacement motors. The accompanying benefits to the operator included increased hole cleaning capacity, torque and drag reduction in tripping times, and reduced risk exposure in the 16-in. sections.
The results obtained with the updated design demonstrated that in the current challenging energy market environment, using proven technologies to challenge decades of best practices can bring significant benefits to the well construction and enhance the performance benchmarks for future wells.