The two principal functions of oilwell cementing are to restrict fluid movement between zones within the formation and to bond and support the casing. Apart from these, the cement sheath also protects casing from corroding, protects the casing from shock loads when drilling deeper, and plugs lost circulation or thief zones. Once cement is placed in the wellbore, initial setting occurs wherein development of compressive strength becomes more important for further drilling operations. Early strength development is important to help ensure structural support to the casing and hydraulic and mechanical isolation of downhole intervals. Delays in strength development cause significant amounts of lost time because of the need to wait on cement (WOC). Typically, an accelerator is often used to enable early strength development in cement. It is desired that an accelerator should improve overall compressive strength without causing excessive gelation. Nanomaterials (being smaller in size and higher in surface area) are used in several fields, including catalysis, polymers, electronics, and biomedicals. Because of a higher surface area, these materials can also be used in oilwell cementing to accelerate the cement hydration process. Moreover, they are often required in small quantities. This paper documents a case in which nanosilica was used in cement formulations to develop high early strength. Nanosilica also helps enhance final compressive strength and helps control fluid loss. Using the correct quantity of nanosilica, it is possible to design cement slurry with low rheology and good mechanical properties while controlling fluid loss.
Downhole CO 2 in the presence of water forms carbonic acid, which reacts with cement. Some of the final products are water soluble and are leached out. This could cause loss of long term mechanical integrity of the cement sheath, among other issues. Hence, long term prediction of cement sheath carbonation is important to help ensure the cement system designed for CO 2 environments creates and maintains zonal isolation throughout the life of the well. This paper discusses a series of long term tests performed to better understand the effects of CO 2 on cement quantitatively. CO 2 downhole generally falls within two categories-dry CO 2 , which is a result of carbon capture and sequestration (CCS) activities, and wet CO 2 , which accounts for naturally formed CO 2 . Cement samples are tested under downhole conditions of high-pressure/high-temperature (HP/HT) in two different environments-supercritical CO 2 and carbonic acid, which represent the two different types of CO 2 present in the wellbore, respectively. Different types of cement blends have been used in the study to understand the effects of cement composition on corrosion caused by CO 2 .Cement samples were periodically withdrawn from the autoclaves to test for transient permeability, compressive strength, Brinell hardness, and chemical composition (X-ray diffraction [XRD], inductively coupled plasma [ICP] tests, pH indicator testing, and thermogravimetric analysis [TGA]). All of the samples were tested for a total of one year. It was observed that chemistry played a very important role in determining how resistant the cement is to attack from CO 2 .This study helped provide clear insight into a method that can be used for testing different cement blends for long-term integrity under varying corrosive environments. Knowing the performance of particular cement chemistry under downhole conditions provided considerable benefit in terms of understanding long term integrity of the cement sheath.
A number of reservoirs around the globe are deep, and often it is necessary to drill and cement through salt zones to reach the reservoir section. Brazil offshore is one example where reservoirs are buried deep, and the salt zones there are quite challenging to drill through and cement. Many of these salt zones contain chemically reactive salts, such as magnesium and calcium chloride, and usually pose unique challenges during placement of the slurry and subsequent cement slurry hydration and compressive strength development. These salts, especially MgCl2, chemically interact with the cement slurry, thereby altering the mechanism and kinetics of cement hydration, leading to premature gelation and shorter thickening times. Mitigating these effects is a challenge and is important to successfully place the cement slurry in the annulus and for the slurry to develop the required mechanical properties, such as compressive strength. In the present study, slurries were formulated to overcome gelation issues with the required compressive strength for successful zonal isolation. The slurries were designed in such a way that they can take up to 12% contamination by weight of water (bwow) of the MgCl2-based salts known as carnalite and tachyhydrite. Pertinent data that characterize performance of these slurries are presented in this paper.
The primary objective of oilwell cementing is zonal isolation (i.e., restricting fluid movement across various zones within formations). Another equally important function is to support casing from various operationally induced mechanical and thermal stresses. To achieve successful zonal isolation, the cement sheath should possess important properties, including low permeability, high early compressive strength, good tensile strength, etc. This article presents a detailed experimental investigation of the effects of various nanomaterials on cement slurry properties. Nanomaterials are used in several fields, including catalysis, polymers, electronics, and biomedical applications. Because of their small particle size, these materials have high surface energy and hence higher reactivity. For this reason, nanomaterials are often necessary in small quantities for enhancing specific properties of the base material. The development of high-performance fluid systems for oil and gas applications is possible through nanotechnology. In recent years, many studies have shown the usefulness of nanomaterials in enhanced oil recovery (EOR) and drilling fluid applications. Investigations have also shown the use of nanomaterials in oilwell cementing. The experimental investigation of the effects of various nanomaterials on cement slurry properties shows that the addition of a mere 1.5% of halloysite increased tensile strength by approximately 141%. Similarly, the addition of nano-alumina resulted in achieving early compressive strength at temperatures as low as 40°F. Hence, these nanomaterials can act as nonchloride-based accelerators for low-temperature applications. Additionally, it was observed that, to obtain the greatest benefit of using nanomaterials, it is necessary to disperse them in desired media before use. The results of this study on the applications of nanotechnology in oilwell cementing provide an opportunity to use nanomaterials for enhanced cement slurry properties with minimal cost.
Expansion additives have been used in cement plugs to mitigate the potential risk of plug failure resulting from shrinkage. These additives are effective only when their amount is tailored for downhole boundary conditions, and their role should be well understood. This work discusses using an improved testing method that enhances the dependability of the volume change measurement and exhibits the impact of test boundary conditions on the shrinking and expanding behaviors of cement plugs. Boundary conditions investigated with this method include temperature, pressure, water access to the cement from the formation, and the role of mechanical constraints. Dependability is demonstrated by verifying the repeatability and reproducibility of the method at two different laboratories. Together with the noninvasive continuous volume change, supplementary measurements, such as ultrasonic compressive strength, tensile strength, and chemical composition analysis, have provided inferences about the mechanism of volume change. The new method embodies all attributes listed in API 10 TR2 (1997), including a constant external stress state in all measurements and a constant pore pressure during total volume change measurement. The results of percentage volume change from this test method present an extremely small variance, highlighting its repeatability; additionally, the measurement was reproducible between laboratories. Expansion value increased with a decrease in confining pressure, and excessive expansion in the absence of an effective confining pressure produced weak samples. The absence of outside water caused cement containing the expansion aid to shrink more than its neat equivalent; such observations highlight the importance of fluid boundary on the action of expansion additives. These observations were possible because the test method can capture temporal and boundary condition effects more aptly. Thus, the improved method provides a dependable measurement for tailoring plug properties.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.