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.
The long term development from four artificial islands of this giant offshore field in the United Arab Emirates (UAE) is requiring longer and longer ERD wells. This can only be achieved by drilling higher angle, higher departure and increasing lateral lengths. Horizontal departure ratios have increased from 2:1 to 3:1 and will, before the development has finished approach 4:1. Maximum Reservoir Contact (MRC) lateral lengths at the beginning of the development were planned to average 10,000ft but are already being lengthened to 20,000ft, and beyond. This paper describes the many challenges that have arisen and have been successfully overcome to enable deployment of 6 5/8" horizontal lower completions of lengths up to 20,000ft into wells that are greater than 30,000ft MD. These challenges have been surmounted through the use of proprietary in-house software, leveraging partner resources and global experience, close collaboration between drilling, completion and field development teams, new technology equipment development and deployment methodologies. Several case histories will be presented and discussed at length in this paper. These will focus on specific aspects for each of the wells such as the; high strength liner connections, high load liner running tools, reservoir drilling fluid composition, swellpacker design, use of drillpipe or casing swivels, centraliser type and the effect of dog leg severity in the long reservoir lateral.
Extended Reach Drilling (ERD) and Maximum Reservoir Contact (MRC) well design can drastically decrease development costs. A critical ERD and MRC challenge is frictional drag encountered when running long casing and liner strings. If the frictional drag becomes too great the string will stall before reaching total depth (TD), severely compromising the completion of the well. This paper presents the implementation of the casing swivel tool to effectively mitigate this friction risk. String rotation can provide a large reduction in axial drag by shifting the friction vector to primarily affect the torsional direction. Full string rotation offers the largest benefit, but the torque required often exceeds both the casing connection rating and top drive capability. The use of a swivel enables partial string rotation above the swivel to reduce the torque requirement. With increasing production lateral lengths the swivel was moved from the running string into the liner to increase the rotating length of pipe while managing rotational torque. The drill pipe swivel has a long history of effectively providing a reduction in axial drag by allowing for the running string to be rotated when running long MRC lower completion liners. As lateral lengths have increased from 10,000 feet up to 20,000 feet in Extended MRC (EMRC) wells, the ratio of liner length to running string length has greatly increased. To accommodate this shift in well design the swiveling point needed to be pushed deeper into the well, from running string to the liner. The fit-for-purpose design of the sacrificial casing swivel allows it to be integrated permanently into the completion and enables increased partial string rotation. To date the casing swivel has been deployed on eight wells, including a world record single-run 6-5/8″ production liner. In one well, the liner stalled and only reached TD after engaging the swivel. The use of the casing swivel has reduced the required well count and capital investment by enabling lateral sections of up to 20,000 feet while also decreasing drilling risk due to less overburden drilling. The application of casing swivel in the Giant Offshore Oilfield Abu Dhabi was a first for this size and length of lower completion liner. The casing swivel has become a key enabler to maximizing the length of production laterals resulting in substantial well construction cost savings.
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