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Collaborating Authors
Manuscript Title: Characterization of Microannuli at the Cement-Casing Interface: Development of Methodology
Ogienagbon, Adijat (University of Stavanger, Norway) | Khalifeh, Mahmoud (University of Stavanger, Norway) | Yang, Xinxiang (School of Petroleum Engineering, University of Alberta, Canada) | Kuru, Ergun (School of Petroleum Engineering, University of Alberta, Canada)
Abstract Formation of microannuli at the interface of cement-casing can create well integrity issues. X-ray CT and Optical microscopy are technological trends that may have potential for direct visualization of microannuli. CT has an advantage of providing non-destructive visualization of microannuli, but its resolution suffers with increase in casing thickness. Conversely, Optical microscopy has the potential of providing higher resolution needed to detect smaller sized microannuli; however, information about microannuli is limited to only a few sections where samples have been sliced. The objective of the current article is to describe a methodology to examine the interface of cement-casing. Experimental work was combined with literature review. This includes both direct visualization methods, evaluation of current trends to better understand the characteristics and geometric variation of relevant leakage paths. We generate test specimens consisting of cement plugs, various steel casing thickness and nano-coated aluminium casings. Hydraulic sealability tests were conducted by injecting water at the cement-casing interface. Flow rates are then interpreted in terms of microannuli aperture and direct visualization of the cement plug-casing interface by CT and Optical microscopy was implemented. The experimental findings of this article will form a basis for studying geometry and size of microannuli as well as modelling of fluid migration.
- Europe (1.00)
- North America > Canada (0.68)
- North America > United States > Texas (0.68)
- North America > United States > California (0.47)
- North America > United States > West Virginia > Appalachian Basin > Marcellus Shale Formation (0.99)
- North America > United States > Virginia > Appalachian Basin > Marcellus Shale Formation (0.99)
- North America > United States > Pennsylvania > Appalachian Basin > Marcellus Shale Formation (0.99)
- (5 more...)
Large-Scale Laboratory Investigation of the Microannulus Behavior in the Casing-Cement Interface
Moghadam, A. (TNO Energy Transition) | Castelein, K. (TNO Energy Transition) | ter Heege, J. (TNO Energy Transition) | van der Valk, K. (TNO Energy Transition) | Orlic, B. (TNO Energy Transition) | Wollenweber, J. (TNO Energy Transition)
ABSTRACT Maintaining the integrity of the annular cement in the wellbore is paramount in successful hydrocarbon exploitation, subsurface energy storage, geothermal energy production, and geologic carbon sequestration. Debonding at the casing-cement interface can create connected flow paths for fluid leakage along the well leading to loss of zonal isolation. Reliable estimates of potential well leakage rates require large-scale experiments at representative wellbore conditions. We investigated the behavior of the cement microannulus under various loading conditions on two-meter long casing segments cemented against a rock analogue. The results show that once a microannulus forms, it remains open at casing pressures as high as 40 MPa. The normal stiffness of the microannulus at the casing-cement interface ranged between 50 and 900 GPa, while the shear stiffness ranged between 0.15 and 0.22 GPa. Axial displacement of the casing did not lead to a significant change in the aperture. However, axial loading in presence of a casing coupling reduced the hydraulic aperture. The results of this work indicate an agreement between experimental leakage rates, model predictions, and leakage rates measured at (abandoned) well sites reported in the literature. The laboratory results on the large-scale samples provide benchmark data for validating well integrity models. 1. INTRODUCTION Wellbores are commonly used as a fluid conduit for applications such as water, gas, and oil production, or waste, energy, hydrogen, and CO2 storage. Drilling a well through various strata creates a risk of fluid communication between different formations. This can lead to contamination of the subsurface water resources or leakage of fluids to surface (Viswanathan et al., 2008; Vidic et al., 2013). To mitigate the risk of leaks, steel casings are placed in a wellbore at several depths. A cement slurry is pumped through the casing which subsequently flows through the annular space between the casing and the formation. Once the cement is set, it provides structural support to the casing and acts as a barrier to flow in the annulus. It is critical to ensure the integrity of the annular cement. This includes ensuring appropriate type of cement is used for the downhole pressure, temperature, and chemical environment (Bennett, 2016). Subsequent well operations could also damage the cement by causing expansion or contraction of the casing resulting from a change in temperature or pressure (Bois et al., 2012). This has been of interest for energy storage, geothermal energy, and carbon sequestration projects, particularly when targeting old oil and gas wells (Zhang and Bachu, 2011; Davis et al., 2014; Miyazaki, 2009). A damaged cement sheath can create a permeable zone around the casing that allows fluids to move upwards. This also exposes the casing to chemical reactions with downhole fluids (Gill et al., 2012) Therefore, it is critical to understand the well conditions that can lead to cement damage and the resulting rate of fluid leakage.
- North America > United States (1.00)
- Europe > Netherlands (0.68)
- Research Report > New Finding (0.49)
- Research Report > Experimental Study (0.49)
- Well Drilling > Casing and Cementing > Cement formulation (chemistry, properties) (1.00)
- Well Completion > Completion Installation and Operations (1.00)
- Reservoir Description and Dynamics > Storage Reservoir Engineering > CO2 capture and sequestration (1.00)
- Health, Safety, Environment & Sustainability > Environment > Climate change (1.00)
Abstract Cement sheaths are among the most important barrier elements in petroleum wells. However, the cement may lose its integrity due to repeated pressure variations in the wellbore, such as during pressure tests and fluid injections. Typical cement sheaths failure mechanisms are formation of radial cracks and microannuli, and such potential leak paths may lead to loss of zonal isolation and pressure build-up in the annulus. To prevent such barrier failures, it is important to study and understand cement sheath failure mechanisms. This paper describes a series of experiments where we have used a tailor-built laboratory set-up to study cement sheath integrity during pressure cycling, where the set-up consists of down-scaled samples of rock, cement and casing. Cement integrity before and during casing pressurization is characterized by X-ray computed tomography (CT), which provides 3D visualization of radial cracks formed inside the cement and rock. We have studied how contextual well conditions, such as rock stiffness, casing stand-off and presence of mudfilm, influence cement sheath integrity. The results confirm that the rock stiffness and casing stand-off determine how much casing pressure the cement can withstand before radial cracks are formed in the cement sheath, where the rock stiffness is significantly more important than casing stand-off. Furthermore, it is seen that the radial cracks in the cement sheath continue into the rock as well. However, when a thin mudfilm is present at the rock surface, the cracks stop at the cement-rock interface, and the cement sheath withstands less pressure before failure. The bonding towards the rock is thus of importance.
- Europe > Norway (0.66)
- North America > United States > Texas (0.47)
- Research Report > Experimental Study (0.84)
- Research Report > New Finding (0.70)
Measurement of Cement In-Situ Mechanical Properties with Consideration of Poroelasticity
Meng, Meng (Los Alamos National Laboratory (Corresponding author)) | Frash, Luke (Los Alamos National Laboratory) | Carey, J. William (Los Alamos National Laboratory) | Li, Wenfeng (Los Alamos National Laboratory) | Welch, Nathan (Los Alamos National Laboratory)
Summary Accurate characterization of oilwell cement mechanical properties is key to establishing long-term wellbore integrity. The most widely used method is curing cement in an autoclave, demolding, cutting, and transferring it to a triaxial compression apparatus. The drawback of this traditional technique is that the mechanical properties are not measured under in-situ curing conditions. In this paper, we developed a high-pressure and high-temperature vessel to hydrate cement under downhole conditions and then directly measure cement Young's modulus and Poisson's ratio without cooling or depressurization. We validated the setup with water and obtained a reasonable bulk modulus of 2.37 GPa under elevated pressure. We proposed a poroelastic method to calculate cement elastic properties accounting for boundary stiffness and changing pore pressure. We compared the in-situ measurements with traditional triaxial compression tests conducted on the same specimen after retrieval from the vessel. The results show that in-situ measured Young's modulus is more than double, and the Poisson's ratio is 20 to 100% higher than that measured by the traditional triaxial method. One mechanism could be that the depressurization and repressurization process in those traditional tests may generate microdefects or induced stresses that weaken cement mechanical properties. Finally, we applied our mechanical properties measurements to cement wellbore integrity analysis by using a thermoporoelastic model. We found that the initial state of stress plays a significant role in maintaining wellbore integrity. With only mechanical properties differences considered, the estimation with traditional measured properties may mistakenly show cement is safe under some pressure and temperature perturbations.
Abstract The annular cement is often subject to temperature variations, for example heating during steam injection, or cooling during CO2 injection or hydraulic fracturing. Fractures caused by thermal stresses may create flow paths through the cement sheath thereby jeopardizing the well integrity. The objective of this work was to experimentally and numerically investigate the effect of thermal cycles and harsh cooling on downscaled wellbore sections with a focus on the cement sheath failure. Downscaled wellbore sections were each prepared by cementing a casing section within a hollow cylinder of Berea sandstone. One specimen was subjected to a thermal cycling program that included cooling to −50 °C and heating to 80 °C. Two other specimens (dry and wet) were used in harsh cooling experiments with solid CO2 and liquid nitrogen. CT scanning was performed before the onset of, during and after the completion of the thermal cycling program or harsh cooling experiments. No differences in the distribution of voids and fractures in the cement before and after the thermal cycling were observed. This indicates that the applied temperature range was not sufficient to cause damage in the cement sheath. On the other hand, the harsh cooling experiment using liquid nitrogen resulted in fracturing of both the cement and rock in the water-saturated specimen. Finite-element simulations reproducing the thermal cycling program used in the laboratory experiment were performed. The simulations have shown that thermal radial stresses at cement/casing and cement/sandstone interfaces were relatively low, i.e., from 0.5 to 1.0 MPa, which might explain the lack of thermal-induced damage in CT images. The simulations also suggest that the radial fracture in the water-saturated specimen subject to harsh cooling was caused by a combined effect of tensile hoop stresses and stresses due to water freezing. The fracture was most likely initiated in the sandstone followed by further propagation into the cement. It is likely that well construction materials and the surrounding formation are water-saturated. Thus, cooling well below 0 °C, which may occur during a CO2 blowout, would increase chances for cement and formation failure.
- Europe (1.00)
- North America > United States > Texas (0.68)