Highly Thixotropic Engineered Cement Solution Helps Overcome Lost Circulation While Drilling Deepwater Exploration Well

Abstract

Abstract Loss of circulation while drilling can significantly increase the cost of drilling a well section. A lost circulation decision tree with robust and proven solutions is a tool that enables operators to address the risks and benefits of the treatments available. This paper describes the use of an engineered cement solution to solve an unexpected total loss of circulation situation without retrieving the drilling bottomhole assembly while allowing well operations to continue, during a deepwater exploration campaign in Mexico. The highly thixotropic engineered cement (HTEC) systems are lightweight portland cement slurries tailored to exhibit low viscosity when shear stress is applied and develop gel strength rapidly as shear is removed. This enables the systems to penetrate formation fractures where rapid gelation occurs, after which the development of compressive strength delivers a hydraulic seal. A pre-drill risk assessment of lost circulation was built, and a lost-circulation decision tree was developed to have LCM solutions readily available, due to the logistics constraints of work in deepwater. An unexpected loss of circulation event occurred in the 12-1/4" hole section, the decision tree called first for an LCM treatment which was unsuccessful, maintaining losses of 500 bbl/h. The HTEC system was pumped through the bottom hole assembly (BHA) and placed at the thief zone via a bullhead squeeze. A conventional cement spacer was used to separate the interfaces. The treatment was spotted at the thief zone and allowed to develop compressive strength for 7 hours, then tagged with the drill bit. The rig was able to break circulation with a rate of 2.4 bpm without recording any further losses. The use of HTEC systems when other LCM systems have had no success, helps reduce drilling fluid cost and rig expenses when correctly engineered. Often a single treatment results in total control of the losses.