Cementing and aerated drilling solutions for curing shallow loss circulation

Abstract

Performing cement plugs in the top-hole section due to shallow losses is expected in any geothermal drilling project. In fact, around 10-20% of the well’s budget is allocated for this purpose. Many factors contribute to this high cost, but the most significant are the long turn around time in between cementing jobs and the high number of plugs needed to seal the losses. This results in significant lost rig time and thus presents a big opportunity for cost reduction measures.
PGPC executed an 11-well campaign in known locations, with offset wells which showed that >20 plugs were required to be able to drill and case off the top-hole section. The primary objective of the team was to reduce the non-productive time associated with these losses. The initial approach was to develop a thick, viscous, fast-set cement plug with a lost circulation material (LCM) pre-flush to create a bridge near the wellbore to improve cement plug performance and also reduce waiting-on cement (WOC) time. Further improvement led to a shift from an LCM-centric approach to cement gelation so the slurry would quickly gel up after pumping was stopped. At this point, the number of cement plugs was already reduced by 88% and the cement turn-around time decreased by 61%.
However, the team pushed further to eliminate shallow cement plugs by employing aerated drilling in the shallow sections. The cement plugs were successfully eliminated by the third well and the campaign was finished without any cement plug operations in the shallow loss zones.