Impact of CO2 corrosion on well integrity is an issue in mature fields of Colombian foothill wells. Concerns in regard to corrosion of casing strings having access only through the existing 7" completion challenged the use of new technology to achieve both: log corrosion on outer strings and do not suspend the well to get a full column of fluid. Therefore, corrosion monitoring was performed through 7" chrome production tubing with a new Electromagnetic Scanning Tool (EMST), in a challenging scenario: shut-in well with 3 outer casing strings with a gas cap in the upper wellbore. The job objectives were first to test the technology to detect metal loss from the outer casing strings as well as loss both inside and outside of production tubing (without pulling the production tubing) and second to establish a base line for future corrosion analysis after the immediate drilling rig intervention for sidetracking. A careful candidate selection was performed based on criticality for CO2 corrosion, completion design, service years and operating status of the well including consequence analysis to get a pilot well for EM logging. In production since 1998, the BA Y16 well was selected to be logged before a thru tubing deepening to reach two other reservoirs and further service conversion from oil producer into a gas injector well; the EMST was run in Q1 2013 and measuring the cumulative thickness up to three strings determining that no external corrosion was present in particular in the section of interest, also the high resolution image showed no presence of internal corrosion. Therefore, a successful operation was achieved meeting the proposed objectives with no HSE incidents and within budget. This technology is proven and has become a solution for further wells where CO2 or bacteria damage has been evidenced including corrosion mapping through chromed and carbon steel in a single run avoiding the excessive costs related to pulling the completion to get access to the outer casing strings.

The evaluation of downhole well integrity is an important business for the oil and gas industry. It is driven primarily by the need to optimize production while maintaining a safe environment despite the inexorable corrosion of casing strings and other harsh downhole conditions. Furthermore, with aging infrastructure, evaluating well integrity to plan plug and abandonment or slot recovery projects is critically important. Many technologies have been developed to address the challenges of evaluating casing and cement integrity under varied downhole conditions. These technologies are necessarily growing increasingly more sophisticated to meet the requirements of evaluating multiple cemented casing strings. In particular, wireline cased-hole logging techniques based on electromagnetic (EM) and acoustic techniques have been applied to casing corrosion and cement integrity evaluation. The acoustic measurement techniques deployed for well integrity evaluation typically include the sonic frequency range of tens of kilohertz up to the ultrasonic frequency range of megahertz. The frequency ranges are appropriate for characteristic resolutions of decimeters down to millimeters for sonic and ultrasonic measurements, respectively. These techniques are sensitive to the elastic properties of materials in the well completion and crucial for assessing zonal isolation. In the domain of evaluating corrosion in one or multiple casing strings, the traditional measurement approach uses EM techniques, which are sensitive to the metal thickness, the electrical conductivity (the inverse of electrical resistivity), and the magnetic permeability of ferromagnetic pipes. The spectrum of common EM casing inspection techniques encompasses a frequency range between quasi-static (direct current) up to about 100 kHz. More recently, transient EM or pulsed-field eddy current tools have been introduced. Specific physics and challenges associated with well integrity measurements must be understood and considered in existing and emerging technology solutions.

TX 75083-3836, U.S.A., fax 01-972-952-9435. AbstractA cluster of fields in the South of Oman consists of heterogeneous platform carbonates at ~4500m depth embedded in salt. These salt-sealed reservoirs have no aquifer support so ultimate recovery will be maximized by injecting miscible gas. During drilling operations, the drilling fluid density has to be high enough to balance the high-pressure carbonate stringers whose pore pressure can be almost lithostatic.When circulating to a lighter completion brine however a huge drawdown is applied to the wellbore causing a microannulus to form between the liner and cement sheath. It is important to close this gap to avoid the miscible gas flowing behind the casing and hence impairing reservoir management. This gas is expected to break through in the higher permeability zones and gas shutoff remedies will be impossible if the casing to formation annulus is not sealed. The increase in ultimate recovery from miscible gas injection will be significantly reduced if gas shutoff in the higher permeability layers is impossible.A special cement was trialed which expands over time to close this micro-annulus. Other cementation challenges include the narrow margin between formation pore and fracture pressures, the wide range of formation permeability, the extremely sour nature of the reservoir fluids and the saltsaturated heavy mud. Multiple cement logging runs were made to evaluate this cement at various times and with various fluid densities in the borehole. The first three logs were made within twenty-one days of pumping the cement; all before the slow cement expansion occurred. The well bore fluid during the first log was mud with a slightly lower density than that used to displace the cement. The log was repeated with a surface pressure applied, and repeated again with a much lighter completion brine giving a 61000 kPa differential to the liner. The micro annulus expected from this pressure change is over 180 micron. This third log showed all the bond apparent in the second log had disappeared. The fourth cement evaluation during a workover was made twenty-one months later, again in the much lighter brine. This final log showed the cement had expanded and the bond was restored.

No abstract

Over time, corrosion in a pipe causes metal loss which reduces the amount of stress a pipe can be exposed to before failure. A radial thickness measurement of the corroded pipe allows for a quantitative analysis of the pipe's strength by identifying areas of significant material loss. The effects of metal loss defects on a pipe compound when the defects are close enough to interact. Thus, the identification and characterization of interacting defects as a defect cluster is required when calculating the remaining pipe strength. A Python-based Techlog* wellbore software platform plugin was developed to provide an analytical workflow to detect and characterize the impact of metal loss defects and defect clusters on remaining pipe strength for downhole wellbore integrity applications. The developed plugin is a fully customizable workflow which can be adapted to any well integrity scenario and pipeline regulatory body standards such as ASME B31G, subsequently meeting clients' reporting requirements. The innovative workflow has additional potential to be ported to completely new applications utilizing various alternative downhole measurements.