This paper discusses the successful design, testing, and application of a new filter-cake breaker technology based on lactic acid chemistry. This technology provided prolonged delay in filter-cake breakthrough time at 220°F, which ensured coverage of the entire open hole, improved uniform filter-cake removal, minimized brine losses, and exceeded the expected production rates in different layers of the offshore Abu Dhabi reservoir. Reservoir characterization was a fundamental component in the identification of the proper solution to maximize the return on investment of the assets. Temperature, permeability, porosity, and the nature of the reservoirs were studied thoroughly to determine one solution to be used in different reservoirs. Drilling fluid characterization (non-damaging with proper bridging package) and a proper filter-cake design were crucial to exceed the targeted production of the reservoirs. The paper discusses all steps from the laboratory testing of the breaker, application in different layers of the reservoir, and results obtained from the applications. Lactic acid precursor was confirmed to be the "one fit solution" to cover the different reservoir layers. Because of its chemical structure, the hydrolysis process is slower than other breaker types currently available, which made it possible to maximize the breakthrough time at elevated temperatures, minimize completion fluid losses, and optimize the completion operations. Equally important, as an acid precursor rather than a live acid, this solution enabled the rig site personnel to implement the solution without affecting the health, safety, and environment (HSE) aspects that are fundamental in offshore locations. The possibility of pumping this solution through the rig pits enabled the jobs to be performed without additional equipment generally required for well stimulation. The achievement of these goals, supported by the higher production observed during the flow-back of the well, demonstrated how this solution maximized the return on investment for the assets located offshore Abu Dhabi. The innovative use of lactic acid chemistry in the breaker, as compared to the conventional formic acid precursor breakers that are widely available, provided superior delay at higher bottomhole temperatures (in this case, 220°F) because of the slower acid liberation rate.
This paper discusses the successful design, laboratory testing, and performance of an innovative, low solids, organophilic clay-free invert emulsion fluid (OCF-IEF) used to drill the reservoir section of an extended reach drilling (ERD) well. This specially designed drill-in fluid helped maintain the key ERD factors within the specifications necessary and set new limits for drilling performance, thus maximizing the horizontal section displacement/reservoir drainage and production output. ERD wells necessitate extensive design, planning, and close monitoring of various parameters to successfully complete the drilling and completion phases and deliver production expectations. While evaluating the feasibility of drilling the longest well in the UAE, establishing appropriate fluid system properties was a key focus area. The rheology profile was optimized for hydraulic management, hole cleaning, and fluid stability. The ground marble bridging package was designed to be minimally damaging. Lubricity and rate of penetration (ROP) maximization was also addressed by designing a low solids OCF-IEF in which the base brine was calcium bromide (CaBr2). This paper discusses the processes used during the planning phase, including laboratory testing and hydraulic simulations, and the procedures followed during the execution phase, which helped ensure trouble-free performance during drilling operations. Proper planning and execution using the best-available drilling practices helped enable the drilling of this record-breaking well, without significant issues that could impact rig time. The selection of an OCF-IEF to provide low equivalent circulating density (ECD) performance in a fragile gel fluid, with low sag risk, was fundamental to achieve the necessary fluid properties. The low solids design helped improve deployment of the weighting material (ground marble) compared to similar fields in which more conventional organophilic clay-based fluids were used. More than 18,000 ft were drilled in nine days with an average ROP of 2,000 ft/D, which set a record ROP in this field. As a result, the drilling operations were completed ahead of schedule and below the authorized financial expenditure (AFE). Additionally, the production rate was five times greater than estimated, thus confirming the anticipated nondamaging property of this OCF-IEF. The OCF-IEF design and performance brought within reach reserves not easily accessible using conventional mud systems and drilling techniques. The increased reservoir drainage resulted in significant productivity gains. This fluid can also be used during other operations to reach new target depths to maximize production.
Extended reach drilling well design is one of the most critical designs to consider for achieving maximum reservoir contact and increasing well production. This paper demonstrates the methodology for delivering an organophillic clay-free, invert emulsion fluid system using calcium bromide in the internal phase, and discusses an innovative breaker package containing an acid responsive surfactant. Results show a significant reduction in metal/metal and metal/formation friction. Furthermore, no change in wettability has been recorded after the formation has been treated with the breaker. Precise quantitative and qualitative testing methods provided milestone results. Phases of design began with API testing, followed by stressing the fluid beyond the normal downstream conditions, then finally using the return permeability apparatus. Testing all fluids against an artificial core, followed by a natural core, gave the operator the projections required to drill such complicated wells. Intelligent software helped to replicate the actual conditions precisely enough to drill and complete these wells with minimum friction, as well as to simulate effective hole-cleaning practices to help enable optimum equivalent circulating density (ECD) management. From planning to execution, valuable observations were recorded. The use of this system resulted in successfully drilling and completing the longest horizontal well in offshore Abu Dhabi. During 2.5 months of drilling and completing time, no critical path time was wasted because of uncertainty or changes to the approved plan. As a result of using non-aqueous fluid, the friction factor was reduced to 0.07. Furthermore, no fluid treatment was necessary to maintain that lubricity beyond the physical properties of the system itself. The unique composition of the delayed acid breaker used in combination with acid responsive surfactant removed any skin or crushed zone around the wellbore. The recorded well producibility was beyond the expectation, and no acidizing was required. For nearly a decade, lubricants associated with water-based fluid types have been engineered, but inver emulsion fluids had not been considered because of their low initial density and issues associated with stimulating the reservoir. This system provides a successfully designed and executed organophillic clay-free, invert emulsion fluid, as well as a state-of-art delayed acid filter cake cleanup package to maximize the return on investment.
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