An Assessment of the Physical and Mechanical Properties of Foamed Cement Generated at a Field Site vs. Laboratory

Abstract

Abstract The objective of this paper is to evaluate the physical and dynamic mechanical properties of foamed cement generated at a field site and compare them to similar cements fabricated within the laboratory. Physical and mechanical properties such as porosity, permeability, Young's modulus, Poisson's ratio, bulk modulus, shear modulus, etc. will be discussed. Mechanical properties were obtained under cyclic confining pressures ranging from 12 – 52 MPa. This paper will document the final results of a long-term project that examined the differences between foamed cements generated with laboratory equipment and field foamed cementing equipment. The cement samples in this study were generated at pressure using field foamed cementing equipment as part of a joint effort between the API Sub-Committee 10 and the National Energy Technology Laboratory (NETL). The samples were characterized using helium porosimetry, ultrasonic velocity, and permeability measurements after they were depressurized. To test the variation in permeability and strength parameters of various foam cements, stepwise loading and unloading experiments were conducted. Effective pressures varied between ≈6.8 MPa to ≈46 MPa in ≈4 MPa increments. Permeability was measured at each effective pressure step to determine the change in flow pathways due to cyclic confining pressures. Dynamic moduli including Poisson's ratio and Young's modulus were calculated to determine the impact of effective pressures on the flexibility of the cement. The data shows that the cement's physical and mechanical behavior varied along the length of the sampling containers. During the initial loading of some of the samples, permeability decreased to a point lower than the initial permeability and stayed constant for the remainder of the pressure cycle, which was observed in previous experiments. However, some of the permeability values increased suggesting that the pressure cycles had permanently reconfigured the internal structure of the samples. Our approach to evaluating foamed cement is somewhat novel in that we have collaborated with the API, operators, and service companies, to obtain foamed cement generated at pressure using field equipment enabling a robust comparison to those generated in a laboratory per the API's RP 10-4B. Not only will the information provided by these comparisons help to facilitate the better design and implementation of foam cement generation processes but it will also help improve the understanding of the physical and mechanical behavior of foam cement.