Top-Hoie BOP: From Design Through Offshore Qualification

Abstract

TOPHOLE BOP From Design Through Offshore Qualification Abstract The paper describes the development and testing of a tool that prevents shallow gas influx from developing into an uncontrolled blowout. After having isolated the gas downhole the tool may be used for circulating in new mud to regain control of the well. Introduction Shallow gas blow-outs have represented a hazard to life, assets and environment ever since the petroleum industry's childhood. Over the years the overall safety level in exploring for oil and gas has increased by the continuous development of new equipment and procedures. As soon as a problem area has been defined it has often attracted the attention of individuals and organisations willing to spend time and money with the objective of developing equipment to bring the industry one step forward in reducing hazards. The shallow gas problem is one of the few that has not found a satisfactory solution although it has been subject to numerous attempts for decades. It has represented a frustration to the industry over these years and the reminders of the industry's shortcoming in this area have been frequent This paper describes the development of a tool, a Tophole BOP (THBOP), that may be the answer to this problem. Once drilling into an overpressured shallow gas pocket the gas will start flowing into the well. Unless the problem may be handled by the immediate pumping of heavier mud the situation will develop into an uncontrolled blowout. The new THBOP will, once it has been decided to activate the tool, close off the annulus and prevent the gas from further flow. Once the situation is under control the tool may be opened for direct sensing of the influx pressure to determine the correct mud weight to circulate into the wellbore. The development of the THBOP started with an idea and has resulted in a tool which is today qualified and commercially available in the market. This paper describes the complete development process and is for clarity divided into two main parts:The prototype developmentThe tool test and qualification. 1. PROTOTYPE DEVELOPMENT Application During drilling through the upper formations for setting the casing that shall accommodate the normal blowout preventer (most normally the 20" casing) there is often a risk of drilling into overpressured shallow gas pockets. In this situation there is no structural barrier available to the driller. Unless he is able to control the well by quickly pumping in heavier mud there is nothing preventing the well from free flow to the surface. P. 323^