Development and Application of Ultra-Low Invasion All-Oil Coring Fluid: A Viable Technical Solution for Preventing Core Contamination

Abstract

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.