Development and Field Applications of a Novel NAF in the Gulf of Thailand

Abstract

This article, written by Special Publications Editor Adam Wilson, contains highlights of paper SPE 158680, ’Pushing the Envelope of HT Drilling Fluids: Development and Field Applications of a Novel Nonaqueous Drilling Fluid in the Gulf of Thailand,’ by Kerati Charnvit, SPE, Abhijart Kongto, Fransiskus Huadi, and Sunil Sharma, SPE, M-I Swaco, and Gerard Simon, SPE, Brent Estes, SPE, and Neil Trotter, SPE, Chevron, prepared for the 2012 SPE Asia Pacific Oil and Gas Conference and Exhibition, Perth, Australia, 22-24 October. The paper has not been peer reviewed. A novel nonaqueous-fluid (NAF) system was designed to provide stable rheological properties with a nonprogressive gel structure and very good filtration control and filter-cake quality in wells where the expected bottomhole static temperature (BHST) exceeds 400°F. The fluid was successful in providing wellbore conditions capable of being fully logged and evaluated and, at the same time, providing effective hole cleaning with minimum effect on equivalent circulating density. The fluid has been successful in wells with temperatures from 400 to 428°F and mud weights from 11.7 to 14.5 lbm/gal. Introduction Historically, conventional NAF systems have had a good performance record in the Gulf of Thailand, providing the necessary fluid and wellbore stability to achieve successful wireline-logging operations. However, when BHST exceeds 400°F, problems have been reported during wireline-logging operation, including difficulties in moving wireline-logging tools to reach the target depth or even getting stuck, which led to nonproductive time (NPT) or loss of tools in several wells. As a result, a more robust NAF that could help minimize the NPT was requested by the operator because numerous wells being planned would have BHSTs considerably above 400°F. The first approach to solve this issue was to review and modify field engineering practices in an attempt to extend the stability of the conventional NAF formulation; however, it was concluded from this initial study that a novel NAF was required for this ultrahigh-temperature condition. On the basis of extensive laboratory testing during fluid-system development, it was determined that the combination of a new nitrogen-free emulsifier designed for thermal stability in excess of 550°F and a filtration-control package comprising a synthetic polymer coupled with a modified naturally occurring polymer provided the most stable fluid up to 525°F. Main Components Emulsifier. A new emulsifier was developed to withstand ultrahigh temperatures and provide low-viscosity, stable emulsions (i.e., low and flat gel structure). The emulsifier also contributes to high-temperature/high-pressure (HT/HP) filtration control and temperature stability of the system. This emulsifier has another benefit over the conventional amine-based emulsifiers because it does not thermally degrade and release ammonia when exposed to ultrahigh temperatures, even if the temperature limit of the product is exceeded.