In the UAE, drilling intermediate sections that contain highly dispersive clays with water-based muds almost always leads to mechanical instabilities in the form of pack-offs and tight spots due to highly laminated shale formations containing a high percentage of kaolinite. Operators have struggled with designing proper fluid systems to successfully drill these sections and have resorted to invert emulsion fluids (IEF) in certain fields, but that is not always an option. This paper presents the development and application of a high-performance water-based mud (HPWBM) that provided the required wellbore stability to drill these challenging shale sections through sealing natural and induced microfractures, and thereby reduced operational cost. Based on extensive testing, technical experts customized the HPWBM system to drill the troublesome sections both in vertical and inclined wells. Multiple stages of testing were completed to understand the shale, including X-ray diffraction analysis, which revealed that mixed layers were present with a high-kaolinite content. The cation exchange capacity (CEC) was low, indicating that the clays were not reactive. The optimized HPWBM formulation included two powerful components for shale stabilization and a third key component to minimize fluid loss into the formation. The customized formulation underwent a complete suite of shale testing, including capillary suction testing, linear swell meter, shale erosion, shale accretion, as well as lubricity testing and stress testing. Proper planning and execution, using best-available drilling practices, enabled the drilling of these challenging wells without encountering any significant issues that could impact rig time and increase costs. The selection of a customized HPWBM to provide shale stability performance and low-fluid invasion was fundamental to achieving the required fluid properties. Using this HPWBM system in these formations helped the operators achieve an average rate of penetration (ROP) of 43.7 fph – which was 62% higher than in the offset well and reach 40° inclination on different wells. There was also a reduction in the total volume used to drill the sections due to lower dilution rates compared to conventional systems. As a result of the lower fluid consumption, the total fluid costs were significantly reduced compared to offset wells. The casing strings were run to planned depth with no recorded issues on the first two wells, and savings of 11 days were achieved when compared to the offset wells in the same field. The customized HPWBM system with superior performance was able to achieve high levels of shale stability and inhibition without which this milestone would not have been possible. It made the possibility to drill these formations with an environmentally friendly, lower cost alternative to IEF a reality, which maximized the clients’ returns by reducing the overall cost of ownership.
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.
Most of the deep water reservoirs in Angola are weakly consolidated sands, requiring sand control, and openhole gravel packing is one of the most widely used sand control techniques in the area, Block 15/06 being no exception. High inclination wells targeting multiple reservoir sections interlayered with reactive shales, relatively low frac window, and prolonged well suspension without well cleanup were some of the challenges that needed to be addressed to ensure completion integrity and well productivity. This paper presents the measures taken during the design and execution phases to address the project challenges, along with an evaluation of completion integrity and well performance. Analysis of the downhole gauge data is detailed for one of the wells as an example, illustrating the importance of including downhole gauges in the completion.
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.
To develop a mature onshore carbonate field in Abu Dhabi and reduce the footprint and cost, an artificial island has been built in shallow water that can accommodate drilling rigs and extended-reach wells. This paper presents a case study of the longest onshore well drilled in Abu Dhabi. Planning to drill such a deep well starts long before execution, using offset well data and extended-reach drilling (ERD) engineering. There were formation and reservoir challenges due to the uncertainty in the earth model in the horizontal section of the well. Hence, it was very challenging to maintain contact with the thin reservoir intervals, without approaching the boundaries. In addition, the limited power available to drive the drillstring and maintain circulation drove the ERD engineering team to find optimum solutions, including drillstring and bottomhole assembly (BHA) design. Furthermore, there was a known risk of differential sticking, which meant that the use of radioactive sources in the BHA was undesirable. The well was planned to be drilled in two runs, using nuclear measurements in the first run and non-nuclear measurements in the second. A well-placement methodology and workflow was developed and integrated with the geological understanding of the target layer. Analysis of offset horizontal wells resulted in the delivery of an optimized BHA design, including careful selection of logging-while-drilling (LWD) technologies, to mitigate the geological challenges. The BHA also included a new generation of intelligent, fully rotating, high-dogleg, push-the-bit rotary-steerable system, to geosteer the well in the thin target layer while maintaining the planned target trajectory with minimum borehole tortuosity by means of real-time drilling optimization. The extended-reach horizontal section was drilled successfully, and the geosteering objectives were achieved with 100% reservoir contact over a 20,000-ft interval, targeting a thin carbonate layer and overcoming the complex geological environment. The well was drilled to a record depth of 32,300 ft. The new intelligent rotary steerable system with automatic cruise control helped to eliminate any well-profile issues, minimize wellbore tortuosity, and maintain aggressive drilling parameters. The nuclear and non-nuclear LWD measurements, including NMR, helped to reinforce understanding of the reservoir properties along the entire section. This success has opened the door for drilling more challenging wells. In addition, it has proved that proper planning and execution can shift the boundaries further and gave confidence to drill even deeper.
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