Combat Total Losses While Drilling Using Engineered Thixotropic Cement Solutions with New Design Methodology: Philippines Geothermal Case Study

Abstract

Lost circulation is the most common and costly problem when drilling a geothermal well with naturally fractured and highly permeable formations. This can result in several unwanted events, including additional costs and loss of well integrity. A new methodology to design an advanced thixotropic slurry has been developed with more stringent criteria to validate the system for combatting losses to weak formations with large fractures. To provide strength to the formation for subsequent drilling and cementing operations, the slurry incorporates effective thixotropic agents to provide good slurry mixability, rapid gel strength, thixotropy behavioral, optimum thickening time with static conditions, and high compressive strength after placement. Being thixotropic, the slurry can also return to a fluid-pumpable state when sufficient force is applied enabling squeeze operation to be performed to further seal and plug the naturally occurring fractures opening. The novel approach was deployed for designing thixotropic slurry, which was implemented flawlessly on one re-entry well. In this well, stuck pipe issue was encountered while drilling 9 7/8-in open hole. Before spotting the first plug as a strong base for kick-off, total losses were encountered with more than 1,000 bbl/hr. Despite multiple attempts using conventional lost circulation material pills and conventional lost circulation cement plugs, the losses still could not be treated. However, an engineered thixotropic cement slurry was pumped and successfully cured the losses in a single attempt. The well returned static and was able to be kicked off successfully. Drilling was resumed until the next section with no losses. Given this success, the new thixotropic cement slurry design has been added into the operator ’s standard operating procedure for tackling losses while drilling Geothermal wells in the future. This approach of using engineered design of thixotropic cement pill system has been proven to be the most effective lost circulation treatment from severe to total losses circulation for geothermal wells in Philippines. The implementation of this solution has resulted in significant reductions in rig time, reduced mud lost while drilling and improved zonal isolation and wellbore integrity during cementing. This paper describes the successful application of a newly engineered thixotropic cement plug that has been developed with a new design methodology and proven successful to combat severe and total loss situations while drilling geothermal wells.