This paper covers the seven year history of the reservoir drilling campaign offshore Abu Dhabi, from the early use of a solids free, brine/water-based mud to the recent application of non-damaging, non-aqueous fluids with micronized acid-soluble ilmenite. Details are provided on the integration of the filter-cake breakers with the various types of drilling fluids, from dormant drilling fluid additives to delayed, pH and temperature activated breakers. The paper will cover on the operational implementation and lessons learned from applying all these fluids, both in the drilling and completion/breaker placement phases and describes the avenues undertaken to achieve these performance goals. Data related to well information, reservoir rock type and completion type was gathered and analysed. Fluid Interaction and other studies were performed to determine the suitable fluid type, formulation etc. Various additional things were taken into consideration such as offset well data, drilling requirements, environmental considerations, logging requirements and likely mud damaging mechanisms. Extensive lab tests were conducted, some of which included compatibility of various fluids, return permeability, changes to the oil-water ratio, internal phase composition (heavier CaBr2 instead of CaCl2) and a micronized, acid soluble ilmenite as a weighting agent. The breaker systems saw the same extent of refinement, from enzymes to delayed organic acid precursors and chelating agents to evaluate the removal of the fluid filter cake by the breaker. Fluids formulations were evaluated and optimized based on observations. Over eighty extended reach drilling (ERD) wells have been drilled using both Reservoir Drill-in Fluid (RDF) systems: water-based mud RDF, and Non-Aqueous Fluid (NAF) RDF, each with specially formulated Breakers. These wells provided lessons learned which contributed to the current design and formulations which are in use today. Friction Factors (FF) obtained using RDF NAF proved to be much lower than those with RDF WBM. The lower friction factors enabled wells with longer horizontal sections within the reservoir to be drilled successfully and at significantly higher Rates of Penetration (ROP). The use of micronized, acid soluble ilmenite also led to achieving lower ECD as compared to sized calcium carbonate. The evolution of breaker formulations also allowed for longer breakthrough time to be obtained which allowed for better coverage of the lateral, better removal of the filter cake, and ultimately enhanced production through improved inflow profiles. The end result of the continuous improvement in reservoir drilling fluid was a first of its kind non-aqueous fluid that combined the desired properties of low rheological profile for ECD management, low coefficient of friction and being non-damaging.

This paper presents a case of study of cementing operations in extended reach drilling (ERD) wells on two artificial islands in UAE. The cementing objectives involved covering and isolating the shallower oil or water-bearing zone, sealing any potential crossflow interval between various reservoirs, and mitigating communication between the 13 3/8-in × 16-in. and 9 5/8-in × 12 ¼-in. annulus. Additionally, the cement will become a secondary barrier planned for the 9 5/8-in. casing to prevent potential exposure of the 13 3/8-in. casing in the event of injection gas percolation. For this case was necessary to design the cement with the necessary mechanical properties to extend the well life expectancy. To accomplish the operation objectives, the formations, well design complexity, and possible complications were considered. Understanding these factors facilitated the improvement in the approach and design to obtain better cementing operations results. To achieve all of the targets, various enhancements were implemented systematically over time, which included adding fiber in the cement spacer to mechanically enhance mud removal, adding corrosion inhibitor and bactericide to protect the casing if fluid remained in the well. Various lead cement slurries were designed with tailored rheology to remain within the established narrow margin between the pore pressure and fracture gradient. A flexible and expandable tail cement slurry system was implemented to increase the likelihood of proper isolation. The expansion of the tail cement slurry after the cement sets and the tailored mechanical properties used to achieve the necessary resilience, provide support for the stresses encountered during the life of the well. Upgraded properties, such as fluid loss, reduced permeability, and static gel strength (SGS) development, were used to mitigate possible influx between formations. Both cement slurries were loaded with resilient fiber to enhance the cement ductility. These strategies combined with software simulations enabled equivalent circulating density (ECD) management, contamination avoidance, friction pressure hierarchy, discernment of the top of cement (TOC), determination of possible channels, and appropriate stand-off design. The application of the solutions combined with outstanding consistent field operational performance enabled the following: Fine-tuning various practices, improving isolation across critical zones, achieving the planned TOC, sealing the formations that could create potential future issues, and reducing the probability of interzonal communication or crossflow. A systematic approach was necessary to achieve all the objectives in these challenging wells and determine which practices and technologies provide the appropriate results. Cementing ERD wells with the challenges previously described is not a standard industry practice. This case study presents the staged application of the enhancements that improved the cementing results. These were inferred by evaluating the operational parameters (density, pumping rate, pressure, volumes, and surface returns) in conjunction with the availability of cement logs (CBL, VDL, ULTRASONIC). The results demonstrated the capability to achieve isolation; Furthermore, the continuous annulus surveillance showed no undesirable sustained casing pressure.

Achieving well integrity relies on achieving zonal isolation among narrowly separated sublayers of the reservoir throughout a long openhole section. This requires flawless primary cementation with a perfect match of optimized fluid design and placement. In a UAE field, there are several challenges experienced while cementing production sections, predominantly due to long open holes with high deviation, use of nonaqueous fluids (NAF) for shale stability, and loss circulation issues while drilling and cementing. The need to pressure-test casing at high pressures after the cement is set and the change in downhole pressures and temperatures during well completion / production phases result in additional stresses that can further endanger the integrity of the cement. Breaking of the cement sheath would lead to sustained annular pressure and compromise the needed zonal isolation. Hence, the mechanical properties for cement systems must be thoroughly tested and tailored to withstand the downhole stresses. A systematic approach was applied that used standard cementing best practices as a starting point and then identified the key factors in overcoming operation-specific challenges. In addition to the use of engineered trimodal slurry systems, NAF-compatible spacers, and loss-curing fibers, an advanced cement placement software was used to model prejob circulation rates, bottomhole circulating temperatures, centralizer placement, and mud removal. To enhance conventional chemistry-based mud cleaning and to significantly improve cleaning efficiency, an engineered fiber-based scrubbing additive was used in spacers with microemulsion based surfactant. Furthermore, a real-time monitoring software was used to compute and monitor equivalent circulating density (ECD) during the cementing operation and to evaluate cement placement in real time. Results of cement jobs were analyzed to define the minimum standards/criteria and then to verify the efficiency of the applied solutions. The 9 5/8-in. casing / liners were successfully cemented using this methodological approach, and lessons learned were progressively used to improve on subsequent jobs. Advanced ultrasonic cement bond logging tools along with advanced processing and interpretation techniques facilitated making reliable, conclusive, and representative zonal isolation evaluation. The cement bond logs showed significant improvement and increased the confidence level towards well integrity. After establishing field-specific guidelines over 2.5 years, continuous success was replicated in every well for all the rigs operating in this UAE field.

Objectives/Scope This paper outlines a new and innovative technology for brine recovery after the displacement of Reservoir Drill-In Fluid Non-Aqueous Fluid (RDF NAF) to Completion Brine and the associated operational, logistical, environmental and economic benefits associated with it. A unique slop treatment technology has been utilized to recover and reuse more than 2,168 bbl per well of expensive contaminated completion fluid to help manage losses and avoid injecting valuable completion fluid into operator's injection well. This has also resulted in reducing impact to the life of the injection well and burden on formation, thereby minimizing impact to subsurface environment and contributing to lower well cost. Methods, Procedures, Process The contaminated brine was transferred from the displacement of RDF NAF to brine and processed using a novel slop treatment technology to reduce the NTU and TSS to completion brine specifications required for completion operations. After displacing the well from RDF NAF to brine, typical contaminants would be RDF NAF and hi-vis spacer (water-based). The oil-contaminated brine was usually transferred to the tanks of the cuttings treatment contractor, treated and injected into the operator's cuttings re-injection (CRI) well. The new procedure isolated the contaminated brine to be processed through the slop treatment technology to separate and remove the oil and solids from the brine. The slop treatment involved passing the contaminated fluid through a decanter, solids particulate filter, three-phase separator and then a polishing filter to process the fluid to the required NTU and TSS specifications. Results, Observations, Conclusions The slops treatment unit was implemented for brine processing in 2020 and since then, the solution has achieved desirable operational, logistical, sub-surface environmental and cost related benefits. 2,168 bbl of expensive, contaminated completion brine has been processed per well, for subsequent reuse in the completion operations. Utilization and implementation of this mechanical process, versus the historical filter press process, at the source has had clear tangible savings that can be achieved in all areas of the operation, due to the capability to process oil-contaminated brine at a higher clarity and also the viscous brine at a faster rate. This new processing strategy allowed the operator to set new standards with regards to the recovery of oil-contaminated brine, in the UAE. Novel/Additive Information This is the first successful processing of oil-contaminated brine to be completed in the UAE utilizing a mechanical technology. This process has established new baselines for the operator to be able to recover oil-contaminated brine. By adapting the existing site-based slop treatment technology, this solution has bridged a gap in the market by using a novel mechanical process to optimize oil-contaminated brine recovery efficiency and maximize returns for operators.