The Evolution of the Non-Damaging Fluids Design and Implementation Offshore Abu Dhabi

Abstract

Abstract 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.