Real-Time Cement Expansion/Shrinkage Testing Under Downhole Conditions for Enhanced Annular Isolation

Abstract

Ongoing problems with sustained annular gas pressure on producing wells wordwide is a prime indicator that more work is needed in understanding how cement system design can impact long-term annular isolation. One important area is the relative expansion or shrinkage of cement systems as they hydrate in the annulus of a well. Most Portland cement systems undergo chemical and bulk shrinkage as they set. A number of chemical materials have been developed that can be added to cementing systems to overcome this shrinkage, and in some cases, even impart a degree of expansion. However, the process whereby the degree of shrinkage or expansion is measured has almost universally been some type of a single point test, performed at ambient conditions. This is typically the case even if the cement sample was first hydrated under downhole conditions. The authors detail new methodology and test equipment that allows for the tracking of cement shrinkage and/or expansion real-time, under downhole conditions of pressure and temperature. The system allows for the application of curing pressures in either an aqueous or non-aqueous environment. Data acquisition is totally computerized and can be maintained for whatever time interval is required, without exposing the hydrating cement to surface conditions. With this new technology, the authors will detail how cement expansion and shrinkage can be significantly different under downhole conditions of pressure and temperature than when measured at ambient conditions. It has also been observed by the authors that cement expansion or shrinkage is a dynamic process that may take many hours or even days before any significant degree of volumetric stability is achieved. Finally, a successful field application of the new testing methodology will be presented as validation for the transfer of this new technology from the laboratory to the real world of oil and gas well cementing. Introduction Service companies and operators alike have become more aware of the many factors that can influence long-term zonal isolation in a cemented annulus. It is now apparent that a significant change in the physical volume of the set cement in an annulus, be it an excessive reduction (shrinkage), or even excessive increase (expansion), can play a major role in the determination of success or failure for long-term annular isolation. In order to better quantify these cement hydration volume changes, the authors have seen the industry progress from days when positive expansion was tested simply by observing if the setting cement would expand enough to break a glass bottle, to their newest micro-processor controlled expansion testor. Over the years, many skilled in the art of oil and gas well cementation have extensively researched the shrinkage that typically occurs when a Portland cement-based annular sealant hydrates, and undergoes a chemical transition from a liquid slurry state to the final set state, which will hopefully effect a long-term seal of the well's annulus. The fact that most typical Portland cement systems will exhibit some degree of shrinkage during this "setting", or hydration process, has been well documented in the literature, and for the most part is now accepted within the industry. The deleterious effects of cement shrinkage on annular isolation have also been well documented. This acceptance is in spite of the fact that there have been a wide variety of tests and devices developed in an effort to quantify both the type, and amount of shrinkage that occurs, without the oil and gas industry ever standardizing testing for cement volumetric changes during hydration.

Simulation of wellbore construction in offshore unconsolidated methane hydrate-bearing formation

“…Cement volume shrinkage occurs due to cement hydration process. The volumes of cement shrinkage reported in the literature varies from 0.1% to 4.5% (Goboncan & Dillenbeck 2003;Backe et al 1998;Justnes et al 1995;Chenevert & Shrestha 1991;Chenevert & Shrestha 1987). This large variance is not only because the cement volume shrinkage is significantly affected by the temperature and pressure conditions and the employed test method (Reddy et al 2009), but also because the reported values often include shrinkage before the initial set of cement (i.e., shrinkage within the thickening time).…”

Preparation and Characteristics of a pH Intelligent Response Blocking Agent for the Microcrack in the Cement Sheath

“…The primary function of cement sheath in oil and gas wells is to achieve interlayer isolation, prevent interlayer channeling, and ensure the safety of oil and gas production. , However, cement is a brittle material that is susceptible to damage from various harsh external environments encountered during its long-term service life, − including oil and gas well stimulation and injection, tectonic movement, fault slip, and formation fluid corrosion. − As a result, the cement sheath may develop microcracks, which can compromise the integrity of the cement sheath and lead to annulus crossflow. Annulus channeling flow is a significant issue that includes oil, gas, water, and other substances, with annulus water channeling being particularly harmful. , The entry of high-pressure formation water into the reservoir can increase water cuts in the exploitation well and even lead to reservoir flooding.…”

Reduction of fluid migration in well cement slurry using nanoparticles

“…In another great research, fundamental factors were evaluated and studied for their effects on cementing that summarized as heat, pressure, slurry weight, particle size, and finally volume fraction of constituents [29]. In 2003, Goboncan and Dillenbeck discussed about cement-shrinkage and proposed that in theoretical side of view shrinkage happened with two states of overall shrinkage and porosity in cement matrix [30]. Also, Mata and Calubayan presented that usage of low density cements based on the hollow glass spheres, can weaken probability of gas migration in weak formations [31].…”