Over the last several years, improved recovery, especially in depleted reservoirs, has prompted many research projects involving operators, service companies and academicians. Recent work on rock-brinehydrocarbon interactions has demonstrated that carefully designed low salinity water injection in carbonate reservoirs has the potential for enhancing oil recovery as much as 15% compared with conventional treated sea-water or produced water injection. The implementation of this step-changing technology requires studies carried out on in-situ condition cores. Ultra-low invasion drilling fluids must therefore be used during the coring process, to preserve the formation in its original state, without altering its fluids composition, water saturation or wettability properties. This paper outlines the philosophies and criteria brought to reservoir coring fluids design, development and application of an All-Oil synthetic-based coring fluid.An All-Oil coring fluid with ultra-low invasion characteristics was developed after extensive lab testing. The fluid properties were optimized based on reservoir properties and challenging bottomhole conditions, which are presented in this paper along with design criteria, fluid characteristics, fluid development methodology, benefits, benchmarks set initially and field application details. Excellent multi-segments collaboration and team work during core planning, fluid development work and on-site fluid maintenance to achieve planned parameters led to operational success and are described in the paper.For the first time in UAE, a major offshore operator cut the cores with ultra-low invasion All-Oil Coring Fluid, which provided excellent stability to coring parameters and performance. The cores were recovered, processed and preserved in as close in-situ condition as possible, eliminating water contamination and preserving the core integrity, all of which are the basic essentials to achieve successful specialised formation flooding studies leading to the EOR Project. 520 feet of cores were cut in the reservoir section over 9 runs, with 100% recovery of high quality and uncontaminated cores. The cores were slabbed, plugged, photographed, packed, waxed and preserved successfully on site for transportation to lab for flooding studies.The fluids' outstanding performance that helped in achieving the coring objectives in this new coring strategy are discussed in the paper and lessons learned are contrasted with conceptual design for future optimisation. Laboratory test results are also presented which formed the basis of a well planned field application.
This paper examines the challenges, solutions and milestones of the hydraulic fracturing based cuttings reinjection (CRI) process implemented on two artificial islands offshore Abu Dhabi. During the development of an offshore field from two artificial islands, disposing of vast amounts of drilling waste and cuttings, generated from almost 100 wells, presented a major challenge. The conventional skip-and-ship for onshore treatment and disposal was technically, logistically, and economically unviable and posed possible future environmental liability. After careful assessment, total containment of drilling waste on the islands through multiple hydraulic fractures in suitable formations, for permanent in-situ waste confinement, was concluded by the operator as environmentally and economically the only sustainable process. Two CRI wells were planned on each island to accommodate an estimated 8 million barrels of drilling waste slurry expected to be generated at the islands. While CRI is a proven technology wherein cuttings are slurrified and injected into sub-surface formations, fracture injections have high risks too. Many failures are known in the industry, including well and formation plugging and waste breaches to sea-bed and near-by wells, with far-reaching consequences and liability to operators. Considering the complexity of the multiple-hydraulic fracturing process that requires careful planning, execution, monitoring, and analysis, a comprehensive geomechanical study was performed to identify and characterize all potential injection formations to achieve successful long-term injection. This was followed by front-end engineering design (FEED), fracture simulations, CRI well design, surface facilities design, slurry simulations, and followed by careful execution. Two CRI wells were drilled on each island. Specifically designed injectivity tests were performed on each well before commencing injection, followed by regular injectivity tests to continuously analyze fracture behavior. A carefully designed slurrification and injection process, incorporating detailed QA-QC at all process stages, was implemented that helped to avoid solids settling, fracture or perforation plugging, uncontrolled fracture propagation, or well integrity issues. About 500,000 barrels has been successfully injected to-date in two CRI wells with injection pressures as per FEED estimates. The paper details also the proactive sub-surface injection monitoring-assurance program built into the CRI injection procedure to continually modify the process as per sub-surface pressure responses, thus proactively mitigating injection risks. Periodical injectivity tests, model alignment studies, temperature logs, and fracture pressure analysis facilitated regular recalibration of the geomechanical model to define fracture-domain sizes, monitor fracture height growth, and estimate residual formation domain capacity as injection progressed. The multiple-hydraulic fracture-based CRI process implemented first time in Abu Dhabi incorporates many unique features which can be applied in similar projects elsewhere. This paper also describes the downhole gauges for accurate pressure-temperature monitoring at perforations, a detailed slurry design, the particle-size distribution for slurry quality analysis and quality control, the sub-surface monitoring-assurance program and regular tests and recalibration studies.
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