Nonaqueous, Nondamaging Fluid Implemented Offshore Abu Dhabi
Authors: Feder Judy 
Published: November 2019

This article, written by JPT Technology Editor Judy Feder, contains highlights of paper SPE 192735, “The Evolution of Nondamaging Fluid Design and Implementation Offshore Abu Dhabi,” by Catalin Ivan, SPE, ExxonMobil; Yousif Saleh Al Katheeri, Melanie Reichle, Khalid Akyabi, James Thomas Ryan, Sheldon Peter Anthony Seales, SPE, and Sigit Kustanto, SPE, ADNOC; Laurie Hayden, M-I SWACO; and Christoper Steele, SPE, ELKEM, prepared for the 2018 Abu Dhabi International Petroleum Exhibition and Conference, 12–15 November, Abu Dhabi. The paper has not been peer reviewed.
This paper covers the 7-year history of drilling-fluids application in a reservoir drilling campaign offshore Abu Dhabi, from the early use of a solids-free, brine-/water-based mud to the recent application of nondamaging, nonaqueous fluids (NAFs) with micronized acid-soluble ilmenite. The complete paper provides details about the integration of filter-cake breakers with various types of drilling fluids, from dormant drilling-fluid additives to delayed, pH- and temperature-activated breakers. The paper describes the steps taken to achieve these performance goals, including changes to the oil/water ratio (OWR), internal phase composition [heavier calcium briomide (CaBr2) instead of calcium chloride (CaCl2)], and a micronized, acid-soluble ilmenite as a•weighting agent.
Development Highlights
A key objective for the offshore Abu Dhabi project was to drill longer horizontal 8½-in. intervals while retaining zero-skin completions. This necessitated reducing the torque and drag and coefficients of friction (COF). Achieving these design criteria required developing a nondamaging, nonaqueous (NAF) drilling fluid complemented with a filter-cake-removal breaker system. Emphasis was placed on the design of an NAF that combined the desired properties of low rheological profile for equivalent-circulating-density (ECD) management, low COF, and nondamaging water-based-mud (WBM) formulation.
Four different generations of breakers for water-based reservoir drill-in fluids (RDF) were developed and used before moving to nondamaging NAF. The NAF went through three iterations in addition to fine-tuning of the breaker package.
Data related to well information, reservoir rock type, and completion type were gathered and analyzed. Fluid interaction and other studies were performed to determine suitable fluid type and formulation. Other factors taken into consideration included offset well data, drilling requirements, environmental considerations, logging requirements, and likely mud-damaging mechanisms. Extensive laboratory tests were conducted, some of which included compatibility of various fluids, return permeability, changes to the OWR, internal phase composition, 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. Fluid formulations were evaluated and optimized.
More than 80 extended-reach-drilling wells have been drilled using both water-based and nonaqueous RDFs, each with specially formulated breakers. These wells yielded learnings that contributed to the current design and formulations.
Friction factors (FFs) obtained using RDF NAF proved to be much lower than those with RDF WBM. The lower FF enabled wells with longer horizontal sections to be drilled successfully and at significantly higher rates of penetration. Using micronized, acid-soluble ilmenite lowered ECD as compared with sized calcium carbonate. Additionally, the evolution of breaker formulations allowed for longer breakthrough time, 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 an NAF that combined the desired properties of low rheological profile for ECD management and low COF, and was•nondamaging.