This development, predominantly from four artificial islands, of a giant offshore field in the United Arab Emirates (UAE) requires Extended Reach Drilling (ERD) well design including extended length liners in order to reach drilling and geological targets of the field and Maximum Reservoir Contact (MRC) well design that can drastically decrease development costs. Despite drilling challenges during well construction process such as losses in UER, shallow aquifer flows in Simsima, key seating issues in the base of Simsima, wellbore instability in Laffan and Nahr Umr shale, losses in Salabikh and etc. the team has managed to deliver the longest well to date in UAE to a depth of 35,800 feet and has set many ZADCO internal records for drilling performance with no HSE events. Through the use of enabling best practices, lessons learnt and new technologies such as Casing Swivel, Fixed-Bonded non-rotating centralizers and 21 days swell packers, the well was drilled and completed 11.3 days under Authorization for Expenditure (AFE). Several major milestones and records were achieved such as record drilling performance (spud to TD), longest 8 ½" hole section (18,800 feet) with one Bit and Bottom Hole Assembly (BHA), 16" surface hole inclination of 56°, deepest set 9 ⅝" casing to 17,000 feet MD, longest single stage 6 ⅝" liner in the world (total length of 19,004 feet at the time). All well objectives have been achieved. Several technologies were deployed to enable the abovementioned records including the use of Fixed-Bonded non-rotating centralizers in tandem with sacrificial casing swivel.
While drilling through the initial section of extended reach drill (ERD) wells in Abu Dhabi where the trajectory requires a high inclination across a recognized loss zone various options were required to be assessed to maximize efficiency while balancing risks. Factors such as loss rate, capability of mixing fluid, necessary density to help prevent flow from a shallow water-bearing zone, and rig time, where all necessary and key factors to consider in the design process. For this UAE field with common losses in the surface casing, brine capping was determined the best solution to continue drilling without generating nonproductive time or creating a possible wellbore instability issue when unable to keep up with building mud to offset mud losses. For wells with a higher inclination angle, when the loss rate reached the point where it was not possible to prepare the fluid to keep up with losses, it was necessary to identify a different solution to cure or significantly reduce the losses and enable the hole section to be drilled without potential operational risks. For vugular/fractured porosity formations, using tailored particle size materials was unsuccessful for curing the losses. Therefore, a unique solution was implemented by combining two different systems to battle the losses: a swelling polymer lost-circulation material (LCM) that hydrates and helps reduce flow velocity into the formation, followed by a shear-rate rheology-dependent cement system that is a tunable and tailored slurry with thixotropic properties, which stops losses and develops low compressive strength. With this combined solution, the drilling process was successfully resumed and completed. The usual loss rate for this particular vugular argillaceous limestone formation is between 600 and 800 bbl/hr while drilling. Once the solution was successfully implemented, losses were reduced to 15 bbl/hr. The technique was performed on a second well, applying the lessons learned from the first attempt, and the unique solution achieved a dramatic reduction of losses to 2 to 6 bbl/hr. The cost and effectiveness of the treatment demonstrated that this solution is best for optimizing the drilling process for this particular condition. Applying a swelling polymer LCM and the shear-rate rheology-dependent cement system cured losses for an argillaceous limestone formation with fractured/vugular porosity. It is the first global application of this combined solution.
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