Cement pulsation is a relatively new technology to counteract the problem of flow after cementing by delaying the development of gel strength and suppressing the loss of wellbore pressure that can cause flow after cementing. A cement testing protocol for cement pulsation and our experience applying it to an actual, instrumented, cement pulsation job in the field are described. The protocol uses conventional mud and cement lab test equipment to measure the mud and cement properties that determine the feasibility of, and allow simple performance predictions for, cement pulsation for a particular field application.
Cement pulsation (CP) is the application of pressure pulses to a recently cemented annulus while the cement is curing. It was originally proposed by Haberman1 as a potential means of suppressing the problem of flow after cementing. Recent full-scale experiments in a test well have demonstrated that the application of pulsation can prevent the development of gel strength in high gel strength, non-Newtonian fluids2. Recent field trials3,4 have demonstrated that cement pulsation delivers pressure pulses that can be detected by pressure sensors installed at the bottom of a cemented annulus and that can delay the development of cement gel strength and therefore can delay or prevent the loss of wellbore pressure that can cause flow after cementing.
Cooke et al5 measured pressures in the annuli of several wells during and following cement jobs. Those tests proved that pressure in a cement column typically decreases as the cement cures. This decrease in hydrostatic pressure is widely accepted as the cause of flow after cementing. The loss of pressure is generally understood to result from the combination of decreasing downhole cement volume due to filtrate losses and/or hydration and increasing cement gel strength opposing fluid movement to restore downhole pressure. The results of this phenomenon may be insignificant, may be flow after cementing that requires remedial cementing to restore wellbore integrity, or in the worst cases, results in a surface or underground blowout.
John Haberman1,6 the inventor of cement pulsation, described the process and its early applications. Recent research to both develop and evaluate the effectiveness of the cement pulsation process has been documented by Newman et al3,4. They provide detailed descriptions of the process, its practical application in instrumented field trials on actual primary cement jobs, and the results of those trials. Analytical modeling of the cement pulsation process to provide improved job design, job monitoring, and post-job analysis has been described by Manowski and Wojtanowicz7, Kunju and Wojtanowicz8, and Chimmalgi9. Although this modeling requires fluid rheology parameters to predict or analyze the performance of a pulsation job, a protocol to measure such parameters did not exist. Therefore the work and the resulting protocol described herein was conducted to correct that shortcoming. The protocol was developed as part of an overall effort to both conclusively evaluate and to develop the cement pulsation technology.
A cement testing protocol for cement pulsation is proposed which is analogous to the pre-job tests performed for conventional primary cementing operations.
