Revolutionizing Complex Casing Integrity Analysis in the Middle East Using High-Resolution Acoustic Imaging Free

The recent deployment of high-resolution acoustic imaging has significantly advanced the region's cased hole well integrity and completion performance assessment capabilities. This novel technology provides submillimetric image-based analyses of features and defects commonly found in oil and gas wells. In a single pass, the fluid agnostic technology captures full-circumferential 3D point clouds of data for up to 55,000 feet of cased hole and quantifies common issues such as inner and outer diameter wall loss, connection damage, and assesses complex components. This technology surpasses traditional inspection devices like multi-finger caliper, magnetic flux leakage, pulse eddy current, and single element rotating ultrasound tools in resolution, accuracy, and visualization capabilities. It enhances operators' ability to quantify corrosion rates, conduct burst pressure analyses, evaluate corrosion inhibitor programs, and prioritize remediation activities. This paper introduces the technology and presents an example of technology deployment, highlighting the significant impact on well integrity assessments and operational decision-making that the technology has provided.

Initially introduced by Robinson et al. (2020), high-resolution acoustic imaging exceeds the resolution and performance of traditional cased hole inspection tools by using solid-state piezoelectric sensor arrays and novel imaging modes to achieve 0.25 mm (0.01 in) imaging resolution. In a single pass, this 2-7/8-in diameter technology provides direct measurements of inner diameter (ID) and outer diameter (OD) wall loss defects in a fluid-agnostic, full-circumferential manner. The acoustic waves are controlled using proprietary software and advanced imaging modes to generate cohesive acoustic wavefronts that capture high-fidelity 3D details of the casing. Current generations of the high-resolution acoustic technology have up to 512 individual transducers arranged around the imaging probe circumference that are controlled in a specific manner to compensate for decentralization and tool eccentricity. This solid-state arraybased probe enables electronic focusing such that multiple casing sizes can be assessed from a single tool run. An image of the highresolution acoustic imaging tool is shown in Figure 1.

This technology provides significant advantages over legacy tools commonly used for well integrity evaluations. Multi-Finger Calipers (MFC), which have been used by the industry for over 50 years, offer low-resolution datasets and require contact with the casing wall which can introduce errors due to dynamic effects and decentralization. Magnetic Flux Leakage (MFL) tools infer wall loss by measuring the loss of magnetic flux and correlate this lost flux signal to known calibration. These devices struggle with complex corrosion patterns, gradual wall loss, and subtle defects like splits and cracks, thereby limiting their effectiveness. Pulse Eddy Current (PEC) devices pulse a magnetic field in the casing to analyze the rate of eddy current decay when the signal is cut off. An average thickness reading is then calculated using calibrated values based on ideal casing specifications. Due to this averaging and non-representative calibration information, PEC tools cannot accurately assess thickness in areas with complex corrosion and varying casing specifications. Lastly, Single-element ultrasonics offer limited spatial resolution and azimuthal coverage, making them less effective in providing repeatable defect detection. Additionally, these tools require multiple runs to swap heads for assessing wells with varying casing diameters. Figure 2 shows an unwrapped thickness heat map of a casing with OD corrosion scanned using legacy single-element rotating head ultrasonics (top image) and high-resolution acoustic imaging (bottom image), plotting well depth vs phase angle. This visual comparison shows how a small percentage of the casing surface is inspected using the legacy device compared to the new acoustic technology. The legacy device's low coverage and low-resolution dataset is likely to miss critical defects and misrepresent the casing's condition and risk profile.

High-resolution acoustic imaging provides direct measurements of ID and OD wall loss defects in a fluid-agnostic, full-circumferential manner and captures direct measurements; it does not require interpretation or calibration. The resulting acoustic data are spatially accurate and three-dimensional in nature. Further information on the imaging methods used in high-resolution acoustic imaging is shared below.

Robinson et al. (2020) showed how capturing diffuse acoustic reflections from a casing ID surface enables this technology to produce high-fidelity textured renderings of the surface, facilitating the detection of corrosion, erosion, scale build-up, and other complex features or components. Figure 3 illustrates the principle of diffuse reflection imaging. Following contact with a defect on the casing surface, the incoming angled acoustic wavefront refracts off the textured casing surface and produces a scattering of diffuse waves. Analyzing the diffuse acoustic signals returned to the angled imaging probe enables the creation of high-fidelity images and direct measurements of the casing's surface at 0.25mm resolution.

This approach creates significant advantages in detecting and measuring small holes, complex corrosion, pinholes, breaches, or other interacting defects. Figure 4 below shows a 3.0 mm pinhole found inside of a region with broader general corrosion. This type of defect is complex and legacy integrity assessment tools would struggle to detect, size, or depict the true nature of the breach.

High-resolution acoustic imaging also measures casing thickness using direct reflection techniques. Direct reflection enables this technology to "see through the steel" and directly measure casing thickness, including assessing corrosion and external wall loss defects.

Figure 5 presents sequential simulation images to explain the process by which casing thickness is measured. A high-frequency wave is emitted from the transducer (frame 1) and travels through the fluid medium towards the casing (frame 2). Energy is reflected immediately after hitting the inner wall of the casing, and some is absorbed by the steel, where it continues to propagate to the outer casing wall (frame 3). The acoustic energy continues to oscillate inside the steel, and with each contact of the inner or outer surface it creates a wavefront that propagates back the sensor for storage (frame 4).

The first signal represents the ID wall profile, followed by any indication of wall loss, and the complete signal of the OD of the casing. By recording the acoustic signal's travel time between the ID, defect, and OD at the probe, and factoring in the known speed of sound in the fluid and casing, a precise map of the casing's ID and OD surfaces can be generated, allowing for an accurate determination of the remaining wall thickness at the defect locations. This method directly measures the ID and OD wall in the time domain.

To better illustrate the high level of detail and image quality achieved through these imaging methods, Figure 6 presents three separate images produced using this technology which depicts a connection parted axially and shifted horizontally. From left to right, the first image shows a sample connection diagram. To the right of this is the unwrapped acoustic intensity view which maps the intensity of the acoustic signal returned from the ID of the casing measured by the solid-state probe. This intensity map is valuable for visualizing breaches and other unique surface texture features that create a visible response compared to the surrounding healthy casing. Next is an axial cross section which slices the well at phase angle positions 180-degrees apart to show the length of the breach. Finally, the figure on the far right shows how 3D point clouds of data are used to generate precise 3D rendering, in this example of the parted connection.

High-resolution acoustic imaging has been adopted by operators globally for use in a variety of critical applications such as completion and production optimization assessments, and imaging wells for a wide array of well integrity issues, including ID and OD wall loss, parted connections, and damage to complex components. These two key applications of this technology are outlined below:

High-resolution acoustic imaging has greatly improved the ability to detect, size, and characterize critical defects that compromise well integrity. The combination of comprehensive and intuitive visualizations with direct measurement at 0.25 mm resolution provides a clear understanding of the root cause of the well integrity defect with the precision necessary for remediation planning. By providing accurate and detailed inspection of the casing ID, OD, and thickness, corrosion, pitting breaches, thread damage, over-torqued and parted casing, perforated/engineered punches, deformation, and ovality, malfunctioning equipment can be reliably identified, understood, and remediated. This comprehensive assessment will result in a decrease in completion operation costs, well downtime, and lost production and only requires a single pass from the acoustic imaging technology.

This improvement in resolution has facilitated advancements in burst pressure calculations. Figure 7 shows the different burst pressure methodologies employed by the American Society of Mechanical Engineers (ASME), ordered from most pessimistic and least accurate to the least pessimistic and most accurate (ASME, 2012). While Barlow and B31G are industry standard calculations for burst pressure, they are also the most pessimistic formulas in the ASME standard.

Legacy inspection devices lack the resolution and run-over-run reliability required to use the advanced Effective Area and RSTRENG methodologies. The high-resolution output of acoustic imaging has facilitated a stepwise improvement in analysis methodology and reduced pessimism. Simpson et. al (2022) demonstrated how the detailed river bottom profiles of defects produced by high-resolution acoustic imaging can be combined with advanced burst pressure calculation methods such as Effective Area and RSTRENG to provide a more accurate burst pressure, especially in complex and interacting defects.

Figure 8 shows four visualizations generated using the data captured by the high-resolution acoustic imaging technology of a casing with a defect. The leftmost visualization is a radial distance map which is uniquely valuable when assessing defects, breaches, or complex components with subtle changes in ID diameter. The following acoustic intensity, axial cross-section, and 3D rendering further detail the defect. The ability to accurately assess defects in terms of surface radial measurement, wall loss compared to nominal casing, and axial and circumferential characterization allows reliable calculations of multiple burst pressure methodologies to be calculated.

Figure 9 shows an example of the advanced burst pressure analysis prepared using this technology. A zoomed-in image of the limiting defect and its river bottom profile is shown in the plot on the right as a blue shape and the calculated burst pressure values on the left in the Limiting Defect Summary. The acoustic imaging tools submillimetric resolution allows the true river bottom profile to be determined and more accurate burst pressure calculations compared to legacy tools where wall loss is given over a depth range – with no shape or specific axial or circumferential sizing. The ability to accurately size this defect's axial length, utilized by the Effective Area calculation, gives a maximum burst pressure close to double that determined by Barlow – where only the maximum defect depth is considered. Differentiators like this allow operators to confidently increase production operating pressures, enabling increased production and revenue.

High-resolution acoustic imaging is the leading technology being deployed to optimize completion designs and production in hydraulically fractured wells by providing operators with dimensionally accurate 3D measurements of perforation entry and exit hole area erosional growth (Figure 10) and assessing plug locations for casing damage. Precise perforation growth and plug damage information allows operators to determine valuable stimulation KPI's, such as Uniformity Index and Proppant Distribution, to unlock the most direct and granular assessment of a hydraulic fracture. To date, over 400,000 perforations and 12,000 plugs have been evaluated and aggregated to form the world's largest and most comprehensive perforation measurement and plug performance.

Laboratory testing was performed to validate the accuracy of the acoustic imaging tool, specifically validating its ability to detect and measure sudden changes in casing thickness. Figure 11 shows the test scanning which was conducted using a machined sample with a constant inner diameter and a stepped outer diameter. The sample measurements were imaged in water and validated using an ultra-high-resolution handheld metrology-grade laser scanner used for localized surface imaging and measurements (Creaform3d. 2024).

Following data collection, measurements of this sample as captured by the acoustic technology and laser scanner yielded the results shown in Table 1. The acoustic imaging average measured thickness is given by combining over 900 measurements both axially and circumferentially across each region of the sample. The average delta in acoustic measurement vs laser scan is 0.005-in, or 0.13 mm. This highlights the accuracy of acoustic measurement techniques, as well as the necessity for this technology due to large tolerances in production casing.

After measuring the thickness captured using both high-resolution technologies, a thickness heat map was generated to visualize the similarity between these devices and their measured data points, Figure 12. The acoustic intensity image variation across a constant thickness region is slightly more than the laser scanner – shown by the patterns in the color mapping. However, Table 1 confirms that the average measured thickness between the laser and acoustic imaging is extremely close. The ability to visually map thickness measurement and defects helps operators better visualize and understand the characteristics of any corrosion or damage discovered downhole. This enables an improved root cause investigation and mitigation implementation.

This novel high-resolution acoustic technology was deployed to investigate several complex well integrity challenges. This section presents an example of well integrity inspection where leveraging advanced high-resolution imaging to assess complex well integrity and completion features. As a result, more informed production and remediation operation decisions could be made and optimized completion programs prepared.

High-resolution acoustics were deployed to assess several complex completions features and the integrity of a 4-1/2-in tubing and 9-5/8in casing. The two primary objectives were to assess the tubing's integrity, with a focus on the Polished Bore Receptacle (PBR), and to quantify the impact of a plasma puncher used to perforate the 4-1/2-in tubing. Following the in-situ tubing assessment, the 41/2-in tubing was removed to allow for manual surface measurements of the punch and direct comparison with the acoustic imaging technology measurements of the punch. With the tubing removed, the integrity of the larger 9-5/8-in casing was subsequently assessed.

A detailed inspection of the tubing punch was completed. Figure 13 and Table 2 summarize this analysis and provide a visual comparison between the high-resolution acoustic intensity view of the tubing punch and the tubing once at the surface. Figure 13 shows two photos taken of the punched tubing at surface (left) and an image of the tubing punch as imaged using the high-resolution acoustic technology (right). The bottom image is an acoustic intensity view of the tubing punch.

Two tubing PBR's were observed and analyzed. Figure 14 displays a high-resolution 3D rendering, acoustic intensity view, and axial cross-section of the upper PBR observed in the scanned interval.

Several instances of notable wall loss were observed. Figure 15 below details the maximum wall loss identified in the well of 78%.

After removing the tubing, the high-resolution acoustic technology was deployed to assess the integrity of the casing, liner hanger, and two Differential Valve (DV) Tools. This analysis determined that the casing was in good condition with no breaches or instances of wall loss greater than 12.5% (nominal API thickness tolerance). Three points of notable ovality were identified, with a maximum of 3.01% as shown in the Figure 16 radial-cross section image. In this image, the nominal casing ID is shown as a solid grey circle and the orange line is the surface of the casing as determined by the high-resolution acoustic imaging technology. The difference between the desired and actual casing surfaces helps to visualize the casing ovality with the measurements L1 and L2 representing the maximum and minimum casing diameters, respectively. A maximum passthrough diameter of 8.40-in was calculated at this depth.

Additionally, the two DV tools were identified and determined to be in good condition. Figure 17 shows an unwrapped radial distance view, acoustic intensity view, and axial-cross section view of the upper DV tool.

Finally, scale deposited on the ID of the casing was identified. Figure 18 below shows a high-resolution 3D model of the casing's ID at one instance of scaling deposition observed on the high side of the casing.

The high-resolution acoustic technology precisely measured the dimensions of the plasma punched hole in the 4-1/2-inch tubing, with downhole measurements successfully verified on surface following the removal of the tubing. Severe wall loss of 78% was detected in the tubing which could be removed from service to ensure the long-term producibility of the tubing string. These images and measurements emphasize the accuracy and actionable data made available through high-resolution acoustic imaging; empowering datadriven decision-making for production and remediation activities. The detailed 9-5/8-in casing analysis confirmed that the casing and two DV tools were in good condition and discovered the presence of scale deposits. Armed with this information, a targeted cleanout operation was designed and executed to remove the ID scaling before re-completing the well with a new tubing string.

The introduction of high-resolution acoustic imaging in the Middle East has provided a novel method for assessing cased hole well integrity and completion performance. This direct measurement technology provides sub millimetric imaging resolution and the run-over-run repeatability required to assess integrity. These direct measurements enable the assessment of metal loss from the casing ID and OD, damage at connections, and other complex downhole components that are unquantifiable by legacy devices. This paper presents the rigorous lab and field validation testing completed, along with an example where technology was deployed the technology to successfully identify, analyze, and repair critical defects to optimize subsequent completion operations and return the wells to production.

The following points summarize this paper's key conclusions:

• High-resolution acoustics provide digitally twinned images of downhole completion components and pipe breaches, which was validated by deploying the technology to image a punched tubing downhole. Following deployment, the punched tubing was pulled from the well to compare the acoustics image with the physical sample. The high-resolution image generated directly matched the physical sample.

• This acoustic technology provides 360-degree ID and OD wall loss measurements and textural maps and was used to identify OD centralizer markings. Using this comprehensive dataset, it was hypothesized that the casing centralizers are the root cause of several casing breaches.

• Legacy technologies lack the resolution and advanced imaging capabilities to complete reliable well assessments in a single run, leading to analysis uncertainty and additional investigation costs. The high-resolution acoustics discovered a large casing breach not detected initially deployed to inspect the well. Using the acoustics data, the well was subsequently repaired.

• Owing to the technology's submillimetric resolution, and being grounded in direct measurement physics, even subtle changes in casing thickness can be measured. This was validated in the lab with the average delta between the acoustics measurement and the laser measurement value being 0.005-in or 0.13 mm.

• The acoustic technology's sub millimetric thickness resolution capabilities were highlighted where the technology was used to determine casing weight.

• Diffuse acoustic imaging is optimal for assessing complex components such as Polished Bore Receptacles, Differential Valves, and casing centralizers.