Settled Barite as a Potential Barrier Material: A Field Case Study

Abstract

Abstract During plugging and abandonment (P&A), sedimented and compacted barite adds considerable complexity to the plugging operation. Casing cut and pull is alone responsible for approximately 50% of the cost to establish a formation-formation barrier. However, if the settled barite in the annulus can be used as an additional barrier element, P&A operations can be simplified, and the cost reduced. With this in mind, it is therefore necessary to investigate the sealing and mechanical properties of settled barite. In this study, settled barite from a field on the Norwegian Continental Shelf is investigated to understand the mechanical and sealing properties of the settled and compacted barite from the wellbore and to compare them with cement properties. Strength and ultrasonic measurements are carried out on cored samples to assess their mechanical properties. Computed Tomography scans give an overview of the sample’s texture, and the Scanning electron microscopy provides insight on the microstructure and changes in the chemical composition of the barite from the oil well. In addition, the cohesion (or resistance to mobilisation) of barite powder is assessed by direct shear strength under various loads using a rheo-powder cell. We start by measuring the mechanical properties of settled and compacted barite, which are relatively similar in all samples. Then, compared with typical cement G, settled barite presents low stiffness and mechanical strength. Finally, we compared the mechanical properties of settled barite powders from the field with those of unused sample from the laboratory. In both cases, the barite powder exhibits low flowability, i.e., it is extremely difficult to mobilize, and this increases with humidity. In this paper, new results on the assessment of settled barite as a barrier material are reported through various mechanical, ultrasonic, and imaging tests of a realistic settled and compacted barite from an oil field and compared to an oil well cement. In this case, we observed that the settled barite has poor mechanical properties for potential use as an additional barrier element. This could be link to the original formulation of the drilling fluids used and the conditions of use in the well.