Cement Mechanical Property Measurements Under Wellbore Conditions

Abstract

TX 75083-3836, U.S.A., fax 01-972-952-9435. AbstractCement integrity preservation during completion, stimulation, production, and even, during well abandonment is of critical importance for an operator from long-term economic, productivity, and safety perspectives. Traditionally, compressive strengths have been considered indicators of cement integrity. However, numerous squeeze cementing jobs regularly performed on completed wells are testament to the poor correlation between compressive strengths and cement integrity. Additional mechanical properties such as tensile and flexural strengths, elastic modulus, and Poisson's ratio are being taken into account with increasing frequency for maximizing the cement sheath performance during the life of the well. Unfortunately, all such measurements are performed on samples that have been cured, either under wellbore conditions (for example, pressure and temperature), or laboratory conditions (for example, atmospheric pressure) but tested at atmospheric pressure and temperature. Such properties may at best be useful for comparing different formulations in the selection process but do not provide information about the cement properties under downhole conditions.Using ultrasonic shear wave and compression wave combination measurements, dynamic mechanical properties, such as elastic modulus, bulk modulus, and Poisson's ratio and compressive strength, are measured under pressure and temperature. These measurements are compared with mechanical properties obtained from load vs. displacement under static conditions and acoustic compression and shear wave measurements at atmospheric pressure and temperature. Correlations are made for several slurries. The results are presented. The results also will present cases where the measurements made using this method demonstrated unique advantages over the conventional load vs. displacement techniques.

Nonlinear Stress-Strain Model for Confined Well Cement

“…This size is commonly used in standards and cement studies [14,42,43]. The height to diameter ratio of 2 meets applicable ISRM, ASTM, and cement testing standards [43], which is considered to be the accepted specimen geometry to test the compressive strength of cement [42,44,45,46,47,48]. Mechanical properties of cement Samples 1 in the uniaxial and triaxial tests were measured using an RTR-1000 triaxial rock testing system (GCTS Co., Tempe, AZ, USA).…”

Pore structure evolution and strength development of G-type elastic oil well cement. A combined 1H NMR and ultrasonic study

“…Ultrasonic measurements were performed with the MPro Ultrasonic analyzer, a commercial instrument (Chandler Model 6265 MPro) [18], that uses shear and compression ultrasonic waves to measure mechanical properties of cement samples cured in situ at elevated temperatures and pressures as a function of hydration time. The elastic modulus, Poisson's ratio, and bulk modulus are calculated from the compressive and shear velocities.…”

“…Experiments were conducted at two different curing conditions: (i) ambient temperature (20°C) and atmospheric pressure, and (ii) at 52°C and 16.6 MPa, simulating temperature and pressure at downhole conditions. On the basis of relationships between the velocities of compressive and shear waves and the material properties of an elastic solid, the device provides the relative compressive strength [18].…”

A Review of Recent Research on Contamination of Oil Well Cement with Oil-based Drilling Fluid and the Need of New and Accurate Correlations

“…The effects of oil-based mud have been investigated in the past, especially to understand how the composition and chemistry of OBF affect cement performance [18]. One of the most common pieces of equipment used for cement mechanical properties is the Ultrasonic Cement Analyzer (UCA), which is a great instrument for describing the cement strength evolution [19][20][21][22][23][24]. For example, in 1993, Harder et al [18] carried out laboratory experiments on 17 ppg density Class H Portland cement consisting of fluid loss additives and friction reducers designed for 200 • F. The cement slurry was contaminated (10%, 20%, 30%) with four different types of OBF, which were prepared in the lab with combinations of two base oils (diesel and mineral oil) and two emulsifiers (standard fatty acid and alkanolamide) as shown in Table 1.…”