'Engineering' Design of Lost Circulation Materials (LCMs) is More than Adding a Word

Abstract

Abstract Curing lost circulation, one of the greatest contributors to drilling non-productive time (NPT), predominately has been addressed by applying particulate lost circulation materials (LCMs) into drilling fluids. Selection of LCM combinations has largely been based on experience and driven by the availability of inexpensive materials on location. With respect to lost circulation control, little time has been invested into engineering the LCM design and the subsequent effect on rheology and suspension properties of the drilling fluid. Also, little to no information is published regarding methods or guidelines for designing LCMs for lost circulation applications. Continuing the effort for better lost circulation treatment design, a holistic engineered approach to designing LCMs for mitigating lost circulation is discussed. Depending on the type of flow path (e.g., formation pores and natural or induced fractures), engineering methods and models are presented for the selection of LCM combinations with an appropriate particle-size distribution (PSD) capable of efficient fracture plugging. Models to estimate the effects of LCM addition on drilling fluid rheology and equivalent circulating densities (ECDs) are presented. For some applications, it is critical to have the LCMs suspended properly in the drilling fluid. A unique LCM suspension model is presented that estimates the optimum drilling fluid rheology required for proper suspension. This model is capable of accommodating any changes in drilling fluid density as well as LCM density, size, or concentration. This holistic engineered approach, when considered during the initial drilling fluid planning phase, can be a valuable engineering tool for engineers when preparing a plan for preventing or curing lost circulation. The effort to bring engineering to LCM design should result in large savings in terms of NPT, which directly translates to reduced cost and more efficient use of available drilling rigs. This paper also presents some guidelines for designing and testing LCMs for lost circulation applications.