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.

It is common to be faced with severe losses prior to cementing the 9 5-8 in. intermediate casing in an offshore field in UAE. Intermediate casing covers weak zones and as a results there is always a high risk of formation breakdown and induced losses while running the casing and before it reaches intended setting point. The average losses experienced during drilling the 12 1-4 in. hole may exceed 100 BPH. The main challenge in the case reviewed in this paper was that the formation was fracturing during casing running, compromising ability to achieve proper zonal isolation and successful cement job execution. To address the challenge a special LCM Spacer system was proposed, designed to minimize or eliminate the losses during the primary cement job by offering superior sealing capabilities. This LCM Spacer system can easily mitigate loss circulation while cementing, based on ultra-low invasion technology forming a barrier across loss zones. It creates a film across formation walls and reduces the loss circulation ranging from partial to total losses on permeable, fragile, weak formation, natural fractures and depleted reservoirs. It also improves wellbore stability and ECD’s along the wellbore and expected loss zones. The LCM Spacer system was designed and implemented based on the well conditions, design guidelines and previously recorded global success of the system applied in similar applications.

Lost circulation (LC) is an expensive and time-consuming problem. It's desirable to minimize losses before cement job to ensure good cement coverage and maximize well integrity. But quite commonly, wells experience induced losses just before cementing, during casing running and circulation. In such a scenario, the options to control losses have been few, with limited results. The paper demonstrates a viable solution that can be successfully applied to reduce or eliminate such induced losses during the cement job. To effectively solve lost circulation with the correct technique, it is necessary to know the severity of the losses and the type of lost circulation zone. In UAE fields, the loss rates range from 150 bbl/h to more than 700 bbl/h in the 17½- and 12¼-in open hole sections. During cementing operations, lost circulation causes reduced top of cement, poor zonal isolation, and risks to drill ahead. To solve this problem, a composite fiber-based spacer system based on a novel four-step methodology was designed using advanced software. Before a field trial, rigorous lab-scale and yard-scale testing was conducted to optimize the application. Initially, no losses were witnessed while drilling the 12¼-in section. But during casing running and circulation, severe losses of 150 bbl/hr were induced. To counter these losses, the specially designed fiber-based lost circulation spacer system was pumped ahead of the cement slurry using standard surface equipment. At the beginning of the displacement—while cement and spacer were still in the casing string—the loss rate increased to 700 bbl/hr (total losses). This high loss rate in the crucial intermediate section would normally have resulted in costly remedial operations, loss of mud and cement, and expensive rig time. It was observed that the loss rate remained at 700 bbl/hr until the lost circulation spacer arrived at the loss zone. Subsequently, the loss rate kept on declining finally resulting in full returns during remaining displacement. The designed excess of cement was received as returns, thereby ensuring the desired top of cement at surface. This proved that the fiber-based spacer was effective in curing the losses. An advanced cement bond log showed complete cement coverage over the entire section. This further proved the spacer's effectiveness in achieving all well integrity objectives. The successful application of the engineered fiber-based lost circulation control spacer during primary cementing demonstrates a reliable solution to the challenge posed by losses induced immediately before a cement job. The system is easy to deliver and design and can plug the fracture network in the formation during the cement job. Globally, this engineered composite fiber-blend spacer has proved to improve performance during cementing operations by healing losses to maximize well integrity.

While drilling an 8.5 in. open hole in the Umm Shaif field, an unexpected fault was encountered across formation ARAB-D2, increasing losses from 15.0 to 40.0 bbl/hr. Initial losses were managed using mud lost-circulation material (LCM) pills; however, losses were observed again while running the liner. It was decided to cement the liner to secure the shoe, with the expectation of being required to perform a remedial operation. The liner was cemented with all precautions to help prevent further loss. By systematically introducing enhancements to the cementing and liner running practices and optimizing the fluid (cement/spacer) design using the latest technology fiber system in the spacer, it was possible to achieve the objective to control losses during the cementing operation. Additionally, securing the shoe and isolating the reservoir zone while preparing for a top-of-liner squeeze and liner perforation, if necessary, to squeeze cement in poorly isolated zones was achieved. Three-dimensional (3D) placement simulator software was used to model the flow rates and the equivalent circulating density (ECD) during the operation, and sensitivity runs were performed to observe worst-case scenarios at different loss rates to optimize volumes, rates, etc. Once the spacer crossed the loss zone, lost-circulation additives (composed of a blend of various additives) began bridging across the zone, enabling the cement slurry to reach the top of liner, where it circulated excess cement. The tagged hard cement above the top-of-liner log exhibited good isolation to the reservoir formation, no remedial operations were necessary for the shoe and top of liner, and no perforations were necessary. Spacer fluids are an environmentally acceptable blend of carefully selected materials, including coarse and tough LCM, fibers, and medium-sized, resilient angular materials. These fluid systems help mitigate losses when cementing across weak, unconsolidated, or fractured formations and carry materials with both high-pressure integrity and compressibility to help ensure tolerance to modifications in fracture size, caused by differential pressure fluctuations, without the materials being dislodged or allowing collapse. These materials are stable and insoluble in water. The spacer fluid system breaks the emulsion of oil-based drilling fluid, water wetting the casing pipe and the formation in preparation for cement bonding. Additionally, such materials resist intermingling of fluids at the interface in the fluid train.

Drilling and cementing operations commonly experience lost circulation (LC), which can result in non-productive time (NPT) and excessive costs. Losses were encountered while performing an offshore workover well operation in the UAE that challenged isolation objectives involving spotting a cement plug through coiled tubing. Selection of lost circulation treatments that may be deployed through coiled tubing is limited, increasing the difficulty in addressing losses. Previous attempts to cure losses and spot the cement plug were unsuccessful. This paper describes the application of a new tailored spacer system (TSS), engineered to reduce formation permeability and prevent lost circulation. Placement occurred through coiled tubing to successfully control losses in the thief zone, enable tagging of cement plugs, and achieve isolation for the zone of interest. The new TSS has been used on multiple cementing operations to mitigate losses, improve circulation, achieve top of cement (TOC) objectives, and eliminate remedial work; however, this case is the first global application of the TSS through coiled tubing in a plugging operation to stop lost circulation. Correctly evaluating and interpreting the well conditions, risk identification, analysis, and communication amongst operations personnel, and execution of good cementing operational practices led to utilization of the new TSS for this specific scenario of placement through the coiled tubing ahead of the cement slurry. Losses were prevented leading to a successful plug operation and enabling cementing goals to be achieved.