Techniques for the Study of Foamed Cement Rheology

Abstract

This paper presents methods and laboratory equipment that enable a more accurate assessment of foamed cement used to provide zonal isolation in oil and gas wells. The rotating cup and rotor viscometer commonly used to evaluate foamed cement rheology can introduce a high degree of error. Such errors can lead to the conclusion that low-quality ("quality" defined as the percent of foam in the slurry) cement foams have lower viscosities than their base fluids; such conclusions have been reported by other research organizations.The following attributes of the "bob and sleeve" conventional rotational viscometer are contrasted to those of a threedimensional (3D) design, referred to as the Fann Yield Stress Adapter (FYSA).• Bob/sleeve can exhibit particle or bubble separation. The FYSA provides 3D mixing to maintain a homogeneous mixture of bubbles or particles. • Bob/sleeve produces "wall slip," a common problem with two-phase fluids. The FYSA minimizes wall slip.• Low rev/min of the bob/sleeve may not create sufficient stress to ensure velocity profile distribution in the bob/sleeve cup, resulting in significant errors. The FYSA provides 3D volume averaging shear-stress/shear-rate regimes.A key feature of the FYSA viscometer is that it directly measures the yield point (YP) of a fluid; therefore, it does not rely on statistical regression of shear stress vs. shear rate data. It also measures shear stress vs. shear rate for a variety of complex fluids.The rheology of foamed cement has a direct impact on the hydraulic properties of the slurry. The advantages of applying foamed cement are • Increased wall shear stress for better displacement of drilling mud from the annulus and removal of filter cake from the wellbore walls • Improved fluid-loss control • Prevention of gas migration and water influx during the critical gel-strength period • Reduced slurry density for protection of weak formations This paper presents rheology-testing results using the FYSA and contrasts FYSA results with those obtained using the bob/sleeve method. IntroductionIn the completion of oil and gas wells, cementing operations are employed to seal the annulus and provide zonal isolation, establishing structural integrity for the wellbore. One of the most critical factors to success in any primary cementing operation is effectively displacing the drilling fluid. In today's oil and gas industry, operators are drilling into more difficult formations and drilling highly deviated, multilateral, and high-pressure, high-temperature (HPHT) wells, which make it harder to achieve effective mud displacement.However, because of its good displacement capabilities, foamed cement can be used in many of such challenging situations to help achieve effective mud removal. In studying its displacement capabilities, foamed cement rheology has been recognized to play a huge role in achieving good mud displacement. Therefore, accurately understanding and measuring the properties and rheologies of foamed cement becomes important.

The Influence of Bubbles on Foamed Cement Viscosity Using an Extended Stokesian Dynamics Approach

“…Due to the discrepancy of the results of Ahmed [41] compared to the other experimental results, they are not displayed here along with the simulated results. Olowolagba [42] reports more accurate experimental foamed cement viscosity results and are used to verify the simulated results. The line fitted through the experimental data of Olowolagba [42] is a second order polynomial fit through the data at the lowest shear rate.…”

“…Olowolagba [42] reports more accurate experimental foamed cement viscosity results and are used to verify the simulated results. The line fitted through the experimental data of Olowolagba [42] is a second order polynomial fit through the data at the lowest shear rate. The simulated data of bubbles suspended in a fluid match the most accurate experimental measurements [42].…”

“…The line fitted through the experimental data of Olowolagba [42] is a second order polynomial fit through the data at the lowest shear rate. The simulated data of bubbles suspended in a fluid match the most accurate experimental measurements [42].…”

“…In the book Well Cementing [10], Chapter 14: Foamed Cement [39] a comment is made about the lack of rheological information and the importance of the data. At the time only one study had been referenced [40] and only two other studies [41,42] have been done since the publishing of that book. Some of the conclusions of the studies contradict each other.…”

“…The most recent study, [42], uses a uniquely shaped paddle rather than a bob and sleeve viscometer to measure the viscosity and yield point. The paddle devise, a Fann Yield Stress Adapter (FYSA), was used to minimize wall slippage that can be an issue with bob and sleeve viscometers [42]. The FYSA is designed to minimize wall slippage, measures higher volumes of material, and keeps the bubbles and cement particles better dispersed.…”