Multi-finger calipers have provided an excellent overview of internaltubing condition for the past fifty years. However, understanding the finedetails of pipe condition over short intervals required familiarity andtraining in interpreting the raw curves produced by these tools. Thedevelopment of digital caliper data and 3D visualization software hasdramatically altered pipe condition evaluation at Prudhoe Bay, Alaska. 3D visualization software allows the average engineer to quickly andaccurately understand the details of localized tubing damage. Additionally, computer processing of digital caliper data supports quick correlation oftubing damage to wellbore geometry, other leak detection logs, previous caliperdata of the same well interval, and cross-correlation of data from differentwells. This has resulted in dramatic improvements to recent wellwork decisions, allowing surgical placement of patches, plugs, and whipstocks. Caliper logshave been used to assess scale buildup prior to coiled tubing scale removaloperations and have been run after removal to evaluate job effectiveness.Additionally, areal corrosion trends and velocity effects have been identified, resulting in recommendations to deter damage. This paper presents several examples of how 3D visualization software hasled to improved wellwork operations based on a study of approximately 500calipers run in the Eastern Operating Area of Prudhoe Bay, Alaska. Introduction Multi-finger caliper tools take measurements of slight changes in tubulardiameter when the fingers come in contact with its surface (Figure 1).Mechanical calipers were originally designed in the 1950's to monitor tubingcorrosion. Real-time digital calipers were developed in the 1990's to monitorcasing wear during drilling operations, dramatically improving on this concept.Since the advent of the digital electronic caliper, analysis techniques havecontinued to evolve into increasingly powerful surveillance tools. History of calipers at Prudhoe Bay, Alaska. Calipers have been usedto inexpensively assess internal pipe condition at Prudhoe Bay for over 25years. Prior to the advent of digital calipers, tabulated reports weregenerated along with the traces of each caliper finger. These "squiggles" (Figure 2) could not be interpreted without significant training and theengineer relied on the caliper company's representative for in-depthanalysis. The introduction of memory multi-finger digital calipers dramaticallyaltered tubing and casing evaluation at Prudhoe Bay. Detailed analysis can nowbe easily performed with software that requires minimal training to use. Since1999, approximately 1000 slickline and coiled tubing-conveyed memory calipershave been run at Prudhoe Bay. Multi-finger imaging tool. Calipers are able to pass through typicaltubing restrictions on a single trip and can record data in the casing stringbelow the tubing, as well as in the tubing itself. The measurements have aresolution of a few thousandths of an inch, an accuracy of +/-0.01 inch, andare not affected by wellbore fluids. Currently, there are four different caliper configurations that can be usedto log various ranges of pipe sizes in a single run. These include conventional40-finger, 2–3/4" OD tools which can log 4–1/2" through 7" pipe sizes, andextended reach versions of the same tool that can reach out to include9–5/8" pipe. Smaller, 1–11/16" OD, 24-finger tools are available in aconventional configuration to log 2–3/8" through 4–1/2" tubulars and inan extended reach configuration to log 2–3/8" through 7" tubulars. While most of these options have been available since late 1999, the40-finger extended reach capability is specific to a new generation of tools.These tools became available in 2006 and can work simultaneously withproduction logging and other diagnostic logging tools. In Prudhoe Bay, thesenewer generation calipers have been run simultaneously with magnetic thicknessinspection tools.

TX 75083-3836, U.S.A., fax 01-972-952-9435. AbstractIn Prudhoe Bay, Alaska, non-rig tubing repairs have become a viable alternative to rig workovers (RWO's) to provide an economic remediation for wells with production tubing by "A" annulus communication. Electricline (EL)-set patches can eliminate tubing communication at a significant cost savings and are particularly attractive in areas where RWO cost is significant, such as offshore, remote, or arctic locations. The advantage of tubing patch repair over a conventional RWO is that there is no need to pull tubing, resulting in the well being returned to service faster. Typical patch deployment costs are less than 5% of the costs for tubing replacement with a RWO. To date, 263 permanent and retrievable tubing patches have been set in 181 wells at Prudhoe Bay. This paper discusses the history of conventional tubing patches at Prudhoe Bay, recommended pre-patch diagnostics, and the use of 3-D advanced caliper viewing software. The paper also provides a systematic approach for the design and deployment of conventional tubing patches.

As well integrity is of utmost importance for personnel safety and environmental interests there is an ever increasing need for tools and systems that verify and confirm the status of wells with suspect integrity. Recent near-surface, outer casing failures caused by external corrosion on relatively new wells in the Kuparuk Field of Alaska prompted research for a non-invasive predictive method to foresee failure and aid repair prioritization. There are a variety of tools and methods available to locate leak points and corrosion inside of tubulars, but very little literature exists concerning external corrosion and damage detection on outer and middle concentric strings of casing. The following method is a valuable qualitative approach used to determine existence and severity of shallow external surface casing corrosion before leaks occur. The technique uses a logging tool that analyzes the variations of metal thickness within three concentric sets of down-hole tubulars and identifies areas where metal loss exists. The metal loss combined with assumed or known internal tubing condition reveals the wells with the highest risk for shallow surface casing leaks. When a high risk area is discovered proactive excavation repair plans can be made before any safety or environmental problems occur. This paper summarizes the tool, technical approach and assumptions, limiting factors, and the remarkable comparison between the metal thickness logs and the actual external surface casing corrosion observed on 12 wells after excavating each up to 27 ft in the Greater Kuparuk Area. Future plans and strategy using the technique are also discussed in the paper. Introduction The Kuparuk field is located on the North Slope of Alaska, approximately 30 miles west of Prudhoe Bay (Fig. 1). The Greater Kuparuk Area (GKA) includes the Kuparuk reservoir as well as several other smaller oil pools in the operating unit. The majority of GKA wells are completed with a conductor casing (CC), a surface casing (SC), a production casing (PC) and tubing. However, about 5% of the 1100 wells in the GKA have a single casing design—only the CC, SC, and tubing are present (Fig. 2). Normally the SC functions as an element of a secondary or tertiary layer of protection between the reservoir and atmosphere. For single casing wells the surface casing is the primary and sometime only layer of protection if there is no packer. Therefore, a degradation of the surface casing resulting from corrosion is considered a serious breach of the integrity of a given well 1. Prediction and mitigation of SC corrosion problems are considered vital steps to maintain the mechanical integrity of the wells, the safety of the personnel, and protection of the environment while maximizing the life of the wells. Cause and Extent of Surface Casing Corrosion Historical records, field investigation and lab results from a previous study (SPE Paper 100432) indicate the near surface casing corrosion is a result of cyclic or consistent moisture ingress of oxygenated water with the annulus between the SC and CC. Elevated well operating temperatures in conjunction with an extremely corrosive environment caused by the soluble salts that leach from the cement create a very aggressive corrosion environment 1. Over the last few years, the aggressive corrosion environment has become increasingly evident as 38 GKA wells have been discovered with severe SC corrosion failures at shallow depths typically less than 30 ft. Most of these corrosion failures are on single casing produced water injection wells. They appear to have a higher failure rate than other GKA wells because they operate at warmer external casing temperatures than multi casing injectors or production wells. To date, 22 of the 38 known failures have been visually inspected and repaired by a process which takes approximately four weeks to complete. In addition to the remaining wells currently waiting for repair, the failure rate is such that several new wells are added to the repair list every year. The driving factor behind running the thickness log was to develop a tool that can recognize and locate metal loss with enough accuracy that it can be used as a proactive tool to prioritize repairs before the corrosion becomes actual leak failures to the environment.

Historically, multi-finger calipers have most often been considered tools for assessing internal corrosive damage to tubing and casing strings or evaluating wellbore obstructions. With the development of high resolution digital tools in the early 1990's and subsequent development of 3D caliper data viewing utilities at the turn of the century, these tools have expanded their roles into more complex well work diagnostic operations. On the North Slope of Alaska, the practice of exploiting new pay zones by drilling and completing side-tracks from existing well bores has grown significantly as the fields mature. The development of coiled tubing drilling and its application to thru-tubing side-track drilling has made a sizeable contribution to the battle against production deline on the North Slope. The practice of utilizing a 'used' wellbore to drill and complete a new well brings an increased need for diagnostics in assessing the integrity of existing completion components, evaluating new drilling practices and confirming the integrity of new completion designs.On Alaska's North Slope, multi-finger calipers have been used extensively in the optimization of thru-tubing side-track drilling and completion operations. Before any drilling begins, they are used to evaluate existing well bores for sufficient integrity to support new drilling/completion operations and cost effective production of the new pay zone. During drilling operations, they are often used to confirm borehole geometry and integrity prior to moving forward with re-completion procedures. Once the new completion components have been installed, multi-finger calipers are used to confirm and document the proper placement and integrity of the new completion components. The development of 3D Visualization tools for multi-finger caliper data has played a key role in extending the utilizing these tools to complex drilling and completion diagnostic applications. The application of 3D multi-finger caliper data visualization toward advanced drilling and completion diagnostic needs on Alaska's North Slope are discussed in this paper.

fax 01-972-952-9435. AbstractAs well integrity is of utmost importance for personnel safety and environmental interests there is an ever increasing need for tools and systems that verify and confirm the status of wells with suspect integrity. Recent near-surface, outer casing failures caused by external corrosion on relatively new wells in the Kuparuk Field of Alaska prompted research for a noninvasive predictive method to foresee failure and aid repair prioritization. There are a variety of tools and methods available to locate leak points and corrosion inside of tubulars, but very little literature exists concerning external corrosion and damage detection on outer and middle concentric strings of casing. The following method is a valuable qualitative approach used to determine existence and severity of shallow external surface casing corrosion before leaks occur.The technique uses a logging tool that analyzes the variations of metal thickness within three concentric sets of down-hole tubulars and identifies areas where metal loss exists. The metal loss combined with assumed or known internal tubing condition reveals the wells with the highest risk for shallow surface casing leaks. When a high risk area is discovered proactive excavation repair plans can be made before any safety or environmental problems occur. This paper summarizes the tool, technical approach and assumptions, limiting factors, and the remarkable comparison between the metal thickness logs and the actual external surface casing corrosion observed on 12 wells after excavating each up to 27 ft in the Greater Kuparuk Area. Future plans and strategy using the technique are also discussed in the paper.