Physics-Based Estimation of Excess Cement Volume using Fluid Loss Modeling and Hydraulic Flow Units

Summary

In this paper, we present a new methodology to determine the required excess cement volume by integrating cementing hydraulics with fluid flow in porous media to achieve the planned top of cement (TOC). Optimizing zonal isolation in primary casing cementing is critical for well integrity throughout field development and abandonment. A key factor is ensuring the cement reaches the intended top, which depends directly on the selected excess volume. Current practices estimate excess cement based on annular volume from wellbore and casing geometry, adding a percentage without accounting for key physical processes such as fluid loss. As a result, existing workflows are largely empirical rather than systematic. With this study, we address this limitation by incorporating fluid loss mechanisms into the calculation of excess cement during both dynamic and static stages of cementing. The proposed methodology identifies intervals susceptible to fluid loss using the hydraulic flow unit (HFU) concept and accounts for complex rheological behavior, including changes in consistency over time. It also incorporates a supervised machine learning model to predict static gel strength (SGS) as a function of temperature, pressure, shear rate, and time. Applied to a case study well, the methodology achieved results with less than 5% relative error, improving the accuracy of TOC placement and enhancing well integrity. Additionally, it provides a detailed assessment of fluid loss volumes, supporting better decision-making in cementing design and making the approach applicable beyond cement to broader fluid loss evaluations. The methodology is currently applicable only to porous formations characterized by Darcy flow and in wells where temperature effects during placement are negligible.