The Effect of Key Cement Additives on the Mechanical Properties of Normal Density Oil and Gas Well Cement Systems

Abstract

Recent advances in oil and gas cementing technology allow for the modeling and prediction of both compressive and tensile stresses upon an annular cement sheath, throughout the life of a well. Given the knowledge of the type and magnitude of stresses likely to be encountered in a specific location in a wells annulus gives designers target parameters for designing the mechanical properties necessary in the set cement to be able to sustain those stresses without failing. Such a mechanical failure in a cement sheath can cause a loss of annular isolation. However, the authors feel the ability to model these stresses is only one-half of the information necessary to design cement systems for long-term zonal isolation. While some good work has been done on certain lower density cement systems in an attempt to develop fit-for-purpose designs with improved tensile and flexural strengths, the authors have found that some wells requiring higher density cement systems, also need cements with "enhanced" mechanical properties. Towards this end, the authors have conducted mechanical properties research of several relatively common cement additives. These included organic materials as well as non-organic materials. For this study, these materials were added to oilfield cements with water contents averaging from 50 to 66 % by weight of cement (bwoc). Besides the more common unconfined compressive strength tests, the samples are also subjected to tensile and/or flexural strength testing. While the API has long ago established procedures for running unconfined compressive strength tests, there are currently no API standards in place covering the testing methodology for tensile and/or flexural strengths of oilfield cements. Accordingly, the authors present not only the mechanical properties achieved with the use of the various materials tested, but also the methodology used to achieve their data. In an effort to more closely scrutinize the effect each individual material has on the mechanical properties of the set cement, each additive is examined independently. Armed with this information, design engineers should be equipped to propose cement systems that produce effective long-term zonal isolation at the induced annular stresses of their own wells. Introduction In the process of oil and gas well drilling various types of cement systems are being placed into the annular space between the casing and the formation. The purpose of this cement is to structurally support the casing string and prevent casing corrosion, as well as to create a competent hydraulic seal for long-term zonal isolation during the entire operational life of the well. As mentioned by Ravi1, the cement should meet a wide range of short-term criteria such as free water, thickening time, filtrate loss, gelling, strength development, shrinkage, etc., as well as certain long-term requirements like resistance to chemical attack, thermal stability and mechanical integrity of the cement sheath. In today's oil and gas fields, it is common to find design engineers who understand that changes throughout the life of a well can significantly impact induced stresses on the annular cement sheath responsible for maintaining annular isolation. Changes in wellbore stresses can affect the mechanical integrity of the cement sheath and can be caused by a variety of different factors such as:production rate changesdepleting reservoirsformation compactionworkoversstimulation treatmentspressure and temperature changessecondary and tertiary recovery methods

Enhancing the cement quality using polypropylene fiber

“…Several previous studies suggested the use of different types of fibers such as the Wollastonite, organic, monofilament, and silicic fibers to improve properties of oil well cement at different conditions, the evaluated fibers were able to improve the strength (Shi et al 1995;Heinold et al 2002;Morris et al 2003;Iremonger et al 2015) and mitigate the loss circulation (Elmoneim et al 2000;Ilyas et al 2012;Al Maskary et al 2014;Arshad et al 2014) of the cement.…”

Effects of Nanoclay and Silica Flour on the Mechanical Properties of Class G Cement

“…32−34 They can be very useful in controlling the hydration reactions of cement slurries due to their higher surface area. 35 These materials can enhance the compressive strength and integrity of the cement sheath, as well as control and reduce fluid losses from the cement slurries. 36,37 There are some applications reported in cement and concrete.…”

“…Nanomaterials are used in the formulation of cement to increase its strength and durability. , Nanomaterials have a wide range of applications in different areas of petroleum engineering, such as exploration, drilling, and production. − They have been used in other science fields such as biomedicines, electronics, polymer science, and catalysis . The application of nanotechnology in the field of oil well cementing can provide solutions to many problems related to integrity and durability of cement slurries. − They can be very useful in controlling the hydration reactions of cement slurries due to their higher surface area . These materials can enhance the compressive strength and integrity of the cement sheath, as well as control and reduce fluid losses from the cement slurries. , There are some applications reported in cement and concrete.…”

New Lightweight Cement Formulation for Shallow Oil and Gas Wells

“…This study is primarily about lightweight cement slurries. Such cement systems, with densities in the range of 4–13.5 ppg, can be designed through nitrogen gas injection, , the addition of water extenders like bentonite and sodium silicate, or replacing proportions of cement with low-specific gravity materials, such as microspheres, fly ash, silica fume, and ground granulated blast furnace slag (GGBFS). , …”