While assessing post-hydraulic-fracture perforation growth using solid-state, high- resolution acoustic imaging tools, it was noted that plug failures were occurring at a high frequency. Though plug failures can be observed from hydraulic fracture surface pressure and flowrate data, the aggregate frequency, causes, and severity of the resulting erosional damage at plug locations was not previously well understood and highly speculative. The sub-millimetric three-dimensional imagery generated from high resolution solid-state acoustic tools significantly improved the industry's awareness of plug failure frequency, mechanisms of failure, and the resulting impact to stimulation efficiency. These acoustic tools helped to uncover the causes and explore possible solutions to failing plugs. This paper presents aggregate data encompassing casing wall loss at over 2700 plug locations and presents emerging trends that appear across the broader dataset. In addition, this paper showcases the usage of high-resolution acoustic imaging in two operator-specific case studies.

High-resolution acoustic imaging has provided a novel means of quantifying casing thickness; the technology assesses both inner and outer diameter wall loss for downhole casing integrity applications. The technology deploys high-density solid-state arrays with up to 512 transducers to achieve sub-degree azimuthal resolution and submillimetric axial resolution with casing thickness measurements down to 0.08-in minimum thickness. This paper provides background on the technological advancement, details of laboratory validation results, exploration of burst pressure calculation methodologies, and a field case study based on the novel technology. Data gathered by the high-density, solid-state transducer array uses acoustic signals to measure both casing thickness and radial measurements in a single pass. The resulting 3D point cloud of data is analyzed with image-processing-based machine learning algorithms. Validation data was gathered from multiple machined and field samples. Machined defect dimensions were varied to test the detection, sizing, and accuracy capabilities of the platform. A field-based case study is presented to provide a comparison between high-resolution acoustic imaging data and computed tomography (CT) scan data. Finally, examples of RSTRENG burst pressure analyses are presented to showcase the advantages and sensitivities of using higher-resolution datasets and higher-accuracy burst pressure methodologies. The high-resolution acoustic imaging platform was found to offer fundamental improvements over legacy magnetic flux leakage (MFL) and single-element ultrasound-based tools. The acoustic technology relies on direct measurement principles; the results are not inferred through calibration. The time-of-flight-based approach permits a single casing string comprised of different diameters, wall thicknesses, and materials to be inspected from a single logging run. The technology is pipe material agnostic and directly measures the casing thickness of ferrous and non-ferrous metals. The electronic platform permits the capture and storage of submillimetric axial resolution which captures penetration profiles of entire defects. The high-resolution and spatially registered datasets have been leveraged to conduct effective area, RSTRENG, and modified B31G burst pressure calculations with greatly improved defect identification, penetration quantification, interaction rule application, and shape characterization. The advancements presented in this paper are highly pertinent to gas storage and carbon sequestration operators who seek integrity management advancements. The potential to extend well life, optimize workover schedules, and better manage gas storage pressure ratings are real-world benefits of the presented technology.

Summary A novel high-resolution acoustic imaging technology was developed for the identification of downhole obstructions, restrictions, and casing damage in real time. This system is the first downhole imaging platform that incorporates an articulated robotic head to capture a dimensionally accurate three-dimensional (3D) view of the area of interest with a 0.00016-in2 resolution. The imaging head can navigate a well with a positional precision of 0.0005-in; it provides a 3D reconstruction of the adjacent casing and any obstruction that may be of interest. These real-time images can be captured in any fluid, including brine, oil, water, drilling fluids, and bitumen. The device can replace conventional lead impression blocks and optical-based cameras, both of which have struggled to provide definitive results in challenging environments associated with hydraulically fractured wells. Multi-axis robotics allows navigation through the area of interest and provides the operator with a real-time assessment of casing condition or fish location; it removes any ambiguity associated with the size, location, and orientation of a well obstruction. The rendered 3D point-cloud of data is displayed in real time to field personnel on surface allowing for operators to start planning and executing remedial action with high certainty before the tool has come to surface. This paper outlines the novel technology background and a case study of field deployment. The tool was deployed in the field as a three-dimensional method to overcome inconsistent, low-resolution, and ambiguous results provided by legacy technologies still used in industry.

High-resolution acoustic imaging technology provides operators the ability to extract submillimetric measurements of perforations at any depth into the casing wall. Due to its three-dimensional nature, submillimetric acoustic data permits the extraction of highly accurate area-based measurements at any radial distance into the perforation, with key distances at the inner and outer casing boundary. This novel technology is fluid agnostic and is unaffected by fluid opacity or clarity. The platforms robust 3D measurement capabilities have made it into an ideal means to evaluate casing and perforations in challenging environments such as hydraulically fractured wells. The integration of high-resolution acoustic imaging into numerous operators’ hydraulic fracture and completions evaluation workflows has resulted in a highly insightful aggregate submillimetric perforation dataset. This large dataset has led to the development of a method to virtually unplug perforations by using a well-specific "perforation entry and exit-hole area correlation". The correlation established can only be extracted using acoustic based imaging as it requires submillimetric resolution of both the ID and OD profile of each perforation Using this correlation, the resulting set of post-frac perforation exit-hole measurements improves an operators’ ability to complete a holistic well completion evaluation, even when well conditions cause perforations to be plugged. The outcome is improved operational insight through the ability to directly compare stages with plugged perforations to those without. This approach can be applied at any point in the well's life cycle, which allows operators to revisit assessments and virtually unplug obscured and proppant-filled perforations. The methodology requires a sound baseline knowledge of the performance of the downhole perforating charges. The baseline is commonly obtained through a calibration stage, which is a stage of charges that are shot but left unstimulated to provide the control measurements for the specific charge in the given well conditions. Current industry performance of downhole perforating charges is investigating through the aggregated dataset of calibration charges. To validate this solid-state acoustic technology and demonstrates its high degree of accuracy for entry and exit-hole perforation measurements, machined samples were scanned with this technology, and with a metrology-grade laser scanner for comparison. This paper presents a novel virtual unplugging methodology, enabled by highly accurate and validated entry-hole measurements, as well as other insights garnered from the aggregate analysis of the world's largest calibration perforation datasets.

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