Abstract
Abstract
Lost circulation (LC) is commonly encountered in drilling and cementing operations and can be a costly problem that increases nonproductive time (NPT). Various methods can be applied to control losses—from applying best operational practices to incorporating LC control materials in treatment fluids and cement slurries. Among the cementing challenges, the loss of circulation can also be associated with poor zonal isolation and becomes more critical when zones between reservoirs should be covered to avoid sustained casing pressure (SCP) in the future and to extend the life of the well.
The application for this tailored spacer was the first one globally. Challenges addressed in the largest offshore field loss zone in the UAE included a high likelihood for losses during initial cementing, narrow equivalent circulating density (ECD) gradient, uncertainty in bringing cement to surface in the casing operation, and zonal isolation between reservoirs, formation, and caprock. As part of the best cementing practices, the design and tailoring of the spacers should be considered. Correct use allows the cement to cover zones of interest with less contamination, and cement properties can develop and interact efficiently with the formation.
Using a tailored spacer fluid system engineered to effectively and efficiently help prevent LC and maintain wellbore stability while preparing the wellbore to receive cement is discussed. The tailored spacer system uses additive synergies to help prevent LC in porous and fractured formations and enables control of rheological hierarchy and wellbore fluid displacement efficiency. The spacer was designed to optimize cementing operations where losses are observed and, in this case, incorporate additional LC materials to help prevent severe losses and achieve the desired top of cement (TOC). The tailored spacer system was pumped ahead of the cement slurry, to reduce permeability across the formation, with superior properties that help prevent fluid loss of the cement to the permeable formations.
Enhancing the cement bond and allowing an effective mud removal differentiate it from a conventional spacer. Using this spacer system enabled cementing goals to be achieved. Cement was brought to the surface, casedhole logs exhibited excellent cement bonding, and no SCP was registered, helping eliminate the need for unwanted remedial operations to secure the zonal isolation, which saves rig time.