Innovative Thixotropic and Reactive Cement Design to Cure Lost Circulation

Abstract The challenges involved with using remedial cementing to cure lost circulation, either in the open hole or behind casing to restore zonal isolation and well integrity are well known. Curing lost circulation has become more difficult, risky, costly and complicated in wells with lithology that contain large natural fractures and cavernous formations. Losses can be both static and dynamic in the range of 100 to 300 bbls per hour and can cause long delays in drilling and completion operations or even lead to uncemented sections that jeopardize zonal isolation. This manuscript focuses on a specific multi-stage reactive and thixotropic train of fluids, adopted from similar lost circulation treatments performed in the past and known to be effective. A train of viscous reactive pills, which consisted of Calcium Chloride brine and Sodium Silicate solution, were pumped ahead of and between each of three progressively thixotropic and aggressive cementing fluids. The train of cementing fluids was comprised of low-density cement with strong thixotropic properties reducing the hydrostatic head and rapidly gelling up against the loss zone when contacting the reactive pills followed by nominal density cement with a stronger degree of thixotropy followed by a normal cement slurry with minimal thickening time. The intermixing of these fluids forms a very rapid gel structure in the lost circulation zone, becoming progressively more and more immobile until the loss zone is eventually filled. The fluid train was deployed and has been in use to cure many lost circulation situations for many different wells. Prior to this deployment, the normal practice was to spot a balanced cement plug in the loss zone, which usually required multiple attempts and delayed operations several weeks and many times the lost circulation remained unchanged. The new method reduced the number of attempts to cure lost circulation and sometimes cured lost circulation on the first attempt. This has reduced the number of sections that require drilling blind and also reduced the amount of uncemented sections behind casing that can lead to corrosion, cross flow and other loss of well integrity. The novelty of the procedure is the combination of many reactive fluids and thixotropic cement slurries instead of just one reactive fluid and one cement slurry and this new method is more effective than the old method.