Innovative and Established LCM Cementing Solutions Combined to Create Novel LCM Cementing Fluid Train

Abstract

Losses to the formation when drilling can lead to non-productive time (NPT), altering the wellbore construction due to unplanned casing points, and well control incidents due to the loss of overbalance pressure. The karstified and fractured carbonate reservoir formations sometimes encountered in the Barents Sea represent a high lost circulation risk. The large vugs (or caves) in these formations can be as large as 50 cm in diameter and cause severe to total losses while drilling. Dynamic loss rates are typically in the range of 30-60 m3/hr and can be greater. A unique lost circulation mitigation (LCM) solution is required for these conditions. An operator which plans to drill through this type of formation is wise to plan effective LCM solutions in order to rapidly cure any losses. The presented method is setting a reactive cementing fluid train downhole that creates an effective blockage in the loss zone. The cementing fluid train is composed of three fluids: sodium silicate, calcium chloride, and an innovative thixotropic and low compressive strength cement slurry designed to rapidly cure loss zones. When the first two fluids come into contact, they instantly form a viscous slush-like precipitate of calcium silicate. The fluid train is designed so the ‘slush’ forms inside the loss zone and creates a base for the cement following behind, allowing the cement to set up inside the loss zone. Together these fluids create the ideal LCM solution to large vugs and cavernous zones. The fluids are pumped through the drill string and the bottom hole assembly after it has been pulled above the loss zone. After the fluids are pumped, a short wait on cement time allows the operator to drill ahead through the cement and continue with the planned well path. The content presents a description of the procedures and successful results from two operations performed in the Barents Sea. The operator cured the loss rate to the necessary level to continue drilling, negating the need for a sidetrack. Furthermore, multiple LCM solutions had failed prior to pumping this fluid train, proving the effectiveness of the solution.

Modeling Lost-Circulation into Fractured Formation in Rock Drilling Operations

“…Consequently, multiple problems may emanate because of the loss severity, such as kicks, wellbore instability, environmental contamination, and formation damage. To mitigate this problem, one procedure is to add lost circulation material (LCM) to the circulation fluid [22][23][24][25]. The LCM fluid properties such as viscosity and density are selected according to the formation type and the subsurface conditions, such as the depth, pressure, and fracture conductivity, among other factors [26].…”

A semi-analytical approach to model drilling fluid leakage into fractured formation

“…One procedure to encounter and mitigate this problem is to add lost circulation material (LCM) to the drilling fluid. LCM is commonly used in drilling applications to reduce and stop lost circulation (Attong et al 1995;Ali et al 1997;Olsen et al 2019;Knudsen et al 2015). The fluid characteristics of LCM, such as density and viscosity, should be carefully selected based on the formation of hydraulic properties such as the conductivity of the thief layers and fractures, among other factors (Luzardo et al 2015;Wang et al 2020;Okoro et al 2020;He and Bu 2020).…”