Novel Low-Solids Shear-Dependent Cement System Used to Cure Severe Lost Circulation while Drilling: A Case History

Abstract Lost circulation in the oil industry is a recurrent and costly challenge, especially in mature fields or weak fracture-gradient zones. Incidents can result in partial to total losses in a variety of formations, including highly permeable, fractured, or cavernous types. In most cases, the first treatment options include using gel or mud pills with lost circulation materials (LCMs). However, this and other solutions currently in the market might not fix severe or total losses. This paper presents a low-solids lost circulation solution that develops rapid gel strength when the shear rate decreases. The gel strength buildup is based on polymers and nanomaterials in the fluid system. In situations where the vein or cavernous zones are large, traditional solutions tend to be ineffective. In such cases, a shear-dependent fluid system can be used that develops gel strength as it enters the larger-flow-area lost circulation zone. This helps prevent the fluid from continuously flowing into the zone. Once the gel strength has developed, the system develops nominal compressive strength to adhere to the formation, helping prevent displacement during subsequent well operations. A mature production field in Santa Cruz, Bolivia presented significant challenges during drilling operations. The low fracture gradient and pressurized gas formation created a narrow operational window, increasing the probability of lost circulation because of the mud density required to avoid fluid influx during drilling. In this scenario, LCMs would not stop fluid losses and were limited to pumping through the bottomhole assembly (BHA). The low-solids lost circulation solution was pumped through the drill bit. Having low solids and low rheology under shear, it can be easily pumped through the drill bit without having to pull out of the hole (POOH). The losses were stopped by using this low-solids shear-dependent (LSSD) fluid system. Subsequently, the primary cementing was performed successfully, and effective zonal isolation was achieved. This helped eliminate non-productive time (NPT) in gas wells in Bolivia. This paper presents a successful methodology, lessons learned, and engineering design to cure lost circulation during drilling operations by pumping a novel LSSD solution through the drill bit. The fluid system contains a low amount of solids; hence, it can be pumped through the drill bit, and the fluid characteristics are such that it will plug trouble zones effectively.