Physical and Mechanical Properties of Field-Generated Foam Cements: Implications for Cement Property Prediction and Modeling

摘要

Properties of foam cement are of particular importance to the zonal isolation and mechanical integrity of wellbore cements used in offshore applications. This paper presents an assessment of physical and mechanical properties of field generated foam cements. These properties are measured to determine the performance of cements generated at field conditions, and for comparison with data sets obtained from laboratory-generated cement. These measured properties are also integral data for the development of empirical relationships used to estimate the properties of cements existing in the wellbore. Measurements of mechanical properties include both dynamic and static testing methods. Dynamic testing of Young's modulus, Poisson's ratio, and other mechanical and physical properties are performed under cyclic effective pressures from 6-48 MPa. Dynamic measuring practices utilize ultrasonic velocity measurements at 4 MPa intervals during pressure cycling. Static methods perform strain measurements under uniaxial loading, and are used for strength analysis and comparison with dynamic measurement results. Laboratory-generated cements were mixed according to API-RP-10B-2 and 10B-4, using a Class H Portland cement system. Field-generated samples were obtained from industry collaborators. Results indicate irreversible changes to permeability and Young's modulus over the course of pressure cycling. These systematic variations provide insight into how foam cement properties may be altered when exposed to pressure variations within the wellbore. Empirical relationships are developed between parameters such as compressive strength, permeability, porosity, p-wave velocity, and Young's modulus for foam cements using linear and non-linear least-squared regression analysis. Preliminary empirical relationships show strong associations between compressive strength and each of the various properties of interest. This is a promising development in efforts to predict the properties of in-situ cements. This assessment of mechanical and physical properties of field-generated foam cement provides an in-depth look at cements generated at simulated in-situ pressure conditions. A comparison of field- and lab-generated cement properties provides information about how representative lab-generated cements are of typically-unavailable field samples. The empirical relationships reported in this study may help to provide, using the few measured properties of placed cements, a method of estimating physical and mechanical properties. This information is intended to aid cement design and wellbore planning for more reliable wellbores.