Our solutions-focused research and development provide innovation to deliver well integrity for the life of the well. Read more about how we are addressing increasing well complexity below.
Quantifying 2D and 3D Fracture Leakage Pathways Observed in Wellbore Cement after Uniaxial Compressive Loading
Simon Iremonger and Jared Taylor, Sanjel Energy Services Inc; Xinxiang Yang, Ergun Kuru, Murray Gingras and Zichao Lin, University of Alberta
Stress-induced fractures in wellbore cement can form high-risk pathways for methane or carbon dioxide leakage yet little to no quantitative information on the impact of these fractures has been reported. To investigate this, scanning electron microscopy (SEM) and micro computed tomography (micro-CT) techniques were utilized to quantify the 2D and 3D geometrical parameters of cement fractures in mature thermal thixotropic cement samples that were subjected to pre- and post-peak compressive stress. A novel simulation method was also proposed to quantify the impact of the stress-induced realistic 3D fractures on the cement permeability.
Results show that: i-) For pre-peak samples, 90% of the 2D fractures have length and width smaller than 100 μm and 5 μm, respectively. Although higher compressive stress reshaped the 3D fractures and increased the fracture length and width, no well-propagated fractures were observed; ii-) For post-peak samples, distinctly visible (> 0.1 mm) well-propagated fractures were generated but failed to penetrate the entire sample, therefore the effect of stress-induced fractures (up to 1.0% strain) on cement sample's permeability is limited; and iii-) CT-based 3D visualization and simulation both show that inclusion of a correctly engineered fiber additive is able to blunt the fracture propagation in cement samples.
We conclude that up to the uniaxial compressive strength, the monotonic compressive stress is not likely to create leakage pathways in wellbore cement since the 2D fractures observed in SEM images are in limited dimensions and the large 3D fractures characterized in CT images have poor connectivity. Inclusion of a fiber additive is expected to enhance cement integrity by limiting the fracture propagation.
Design and Application of a New High Performance Lightweight Thermal Cement
Jared Taylor and Simon Iremonger, Sanjel Energy Services.
Lightweight cements offer significant performance benefits over conventional higher density cement blends, including; improved mechanical properties and stress resilience, lower thermal conductivity, lower ECDs and improved returns to surface and potentially lower risk of casing collapse due to trapped annular pressure. However, a number of challenges exist in developing lightweight blends for thermal applications specifically concerning achieving short wait on cement at low bottom hole static temperature while also ensuring long-term chemical and mechanical stability at high temperatures. Here we report the development of a new lightweight thermal cement by utilizing hollow glass microspheres. Further fine-tuning of the desired slurry properties including controllable thickening times, zero free water, low fluid loss and short WOC was achieved through cost-effective additive adjustment, and the mechanical properties of the cement we validated by long term curing at both ambient and high temperaures (340 °C). To ensure that the high performance achieved in the controlled lab environment was maintained once deployed at full-scale field level an extensive QA/QC program was undertaken. This process involved collecting dry bulk field samples and confirming performance (thickening time, free water, rheology and fluid loss) prior to every job. After initial optimization of the blending process, a 100% success rate was achieved over the course of a more than a twenty jobs. Overall, a high quality lightweight thermal cement with excellent long-term mechanical properties was successfully developed and deployed.
Direct Strain Mapping of a Cement Sheath; A New Tool for Understanding and Preventing Cement Failure in Thermal Wells
Simon Iremonger, Sanjel Energy Services; Benjamin Cheung and Jason Carey, University of Alberta
The design and application of a new cement integrity validation test apparatus for improving thermal cement integrity will be presented. This novel approach allows direct strain mapping of to-scale cement sheath as it deforms under different wellbore stress scenarios. Not only does this novel technique provide insight into elastic cement deformation but also helps elucidate how cracks form and propagate as the cement sheath deforms. Strain mapping is achieved through Digital Image Correlation (DIC) utilizing dual high speed and resolution camera systems. Reliably capturing crack initiation in the frame of view of the stereo camera system proved to be a significant challenge. After multiple design iterations, the best results were achieved with creating a predefined defect site in the cement sheath. Detailed crack initiation and propagation strain maps were created for thermal cements with and without fiber additives. This testing demonstrated how fibers are able to blunt crack propagation and dissipate energy through a fiber pull out mechanism leading to a more ductile failure. Early results are promising and are consistent with previous tests showing an increase in ultimate failure strength in tensile samples with fiber additives.