Slickline-Retrievable Wellhead Plugs and Downhole Plugging System Provides Wellbore Integrity for Extreme HPHT Environments

Abstract

Abstract Trends in offshore exploration continually push the definition of high pressureand high temperature in regards to oil and gas well completions. Recentdiscoveries in the Gulf of Mexico (GOM) are opening up vast reserves of naturalgas and these discoveries are again challenging that definition. To meet theneed of high-pressure, high-temperature (HPHT) applications in general and foran operator in one such HPHT field, an ultra high-pressure and high-temperaturerated wellhead plug and downhole plugging system has been developed to providewellbore integrity in extreme conditions. This paper addresses the challenges associated with development ofslickline-retrievable equipment rated to 25,000 psi at temperature extremesfrom 32°F to 450°F and the approaches used to overcome those challenges. Areview of design considerations, sealing technology, design verification, andvalidation testing that exceeds industry standards, is also provided. Introduction While the industry is rising to meet global demands for energy, the reservesneeded to fill that demand are increasingly in more challenging geologies suchas deeply buried reservoirs. Drilling to unprecedented depths is opening a newfrontier of pressure and temperature extremes. To appreciate the growth ofactivity in deeply buried reservoirs, according to the Energy InformationAgency, deep gas production in the US in 1999 was 7% of total production and in2010 an expected rise to 14% of US total gas production. In another industrystudy, the number of HPHT wells drilled from 1982 to 2010 was just over 300wells, while the forecast from 2011 to 2019 was to increase that total to over900 wells with a global geomarket distribution. For many years, HPHT was commonly defined as 10,000 psi pressure and 300°Ftemperature or greater. The move into these new frontiers has moved beyond thetraditional definition of HPHT. One such classification structure is shown herein Table 1 with three levels of HPHT regimes. It is the move into the extremeand ultra HPHT regimes that is driving new methodologies of analysis andvalidation to ensure wellbore integrity in these very challengingenvironments. As the scope of HPHT has expanded, the challenge facing the industry is how toprovide for wellbore integrity under such extreme conditions. This was thechallenge for one service provider to design and develop a wellbore pluggingsystem from the wellhead down to the bottom of the production tubing. To thisend, a unique landing nipple and slickline deployed plugging system wasdeveloped specifically for HPHT, capable of operating in all three regimes. Thenipple and plug system discussed in this paper was developed for a project inthe GOM and is rated to 25,000 psi and 450°F. The plugs incorporate a pumpthrough capability while also accepting a prong to convert to a positive plug. Key operational issues to minimize risks were also addressed.