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Borehole imaging devices are currently available for both wireline and loggingwhile-drilling (LWD) environments for use in both openhole and cased wells. Most wireline, and all LWD devices provide indirect images that are derived from a high-density grid of electrical or ultrasonic acoustic measurements. Optical techniques, such as television and photography, provide direct images of the borehole. Imaging devices consist of (1) a rotating sensor (acoustic or electrical) that scans the borehole with each revolution, (2) multiple, azimuthally placed sensors, or (3) a downhole television or photographic camera. Advances in digital acquisition and processing permit real-time display and evaluation of images of the open borehole or the inside of casing. The resolution and borehole coverage of microelectrode devices has increased with newer designs that allow additional measurement sensors per pad, additional pad segments on a four-arm tool, and the introduction of sixarm imaging tools. In nonconductive borehole fluids, a four-arm microinduction device can provide crude images. Macroelectrode imaging tools (laterolog-type; wireline) provide lower-resolution electrical images from either an azimuthal arrangement of sensors around a mandrel (wireline), or from azimuthally sensitive sensors (logging-while-drilling), that scan the borehole during rotation of the bottomhole assembly. In acoustic imaging, recent devices incorporate design changes that provide improved image resolution and operate in a wider range of borehole conditions. Ultrasonic transducers now use lower transmitting frequencies and spherical focusing and these tools also offer surface-selectable acquisition parameters. Acoustic and microresistivity imaging techniques measure different physical properties and these data are complementary. One recently introduced wireline service combines microresistivity and acoustic imaging devices in a single tool for simultaneous, single-pass acquisition. Recent advances in cable and sonde design permit downhole video in a wider range of petroleum environments, in flowing wells, and in tubing. Openhole image interpretation involves qualitative (visual) identification and quantitative characterization of strike and dip on planar features, lithology, bedding, fractures, and vugs. When core is available, features identified on log-derived images can be correlated or calibrated to it, or when core is absent, images may serve as a substitute. Borehole images are useful in formation evaluation (when calibrated), sedimentology, stratigraphy, and structural analysis. Current applications include core orientation, 'reconstructing' missing core, identification and characterization of fractures and depositional features (e.g. bedforms), reservoir architecture, bedding, grain size, porosity, permeability, net sand and net pay counts, faults, folds, and fractures (hydrocarbon, water, geothermal wells, and in rock engineering), evaluation of borehole stress (borehole stability), directional placement of wellbore for optima...
Borehole imaging devices are currently available for both wireline and loggingwhile-drilling (LWD) environments for use in both openhole and cased wells. Most wireline, and all LWD devices provide indirect images that are derived from a high-density grid of electrical or ultrasonic acoustic measurements. Optical techniques, such as television and photography, provide direct images of the borehole. Imaging devices consist of (1) a rotating sensor (acoustic or electrical) that scans the borehole with each revolution, (2) multiple, azimuthally placed sensors, or (3) a downhole television or photographic camera. Advances in digital acquisition and processing permit real-time display and evaluation of images of the open borehole or the inside of casing. The resolution and borehole coverage of microelectrode devices has increased with newer designs that allow additional measurement sensors per pad, additional pad segments on a four-arm tool, and the introduction of sixarm imaging tools. In nonconductive borehole fluids, a four-arm microinduction device can provide crude images. Macroelectrode imaging tools (laterolog-type; wireline) provide lower-resolution electrical images from either an azimuthal arrangement of sensors around a mandrel (wireline), or from azimuthally sensitive sensors (logging-while-drilling), that scan the borehole during rotation of the bottomhole assembly. In acoustic imaging, recent devices incorporate design changes that provide improved image resolution and operate in a wider range of borehole conditions. Ultrasonic transducers now use lower transmitting frequencies and spherical focusing and these tools also offer surface-selectable acquisition parameters. Acoustic and microresistivity imaging techniques measure different physical properties and these data are complementary. One recently introduced wireline service combines microresistivity and acoustic imaging devices in a single tool for simultaneous, single-pass acquisition. Recent advances in cable and sonde design permit downhole video in a wider range of petroleum environments, in flowing wells, and in tubing. Openhole image interpretation involves qualitative (visual) identification and quantitative characterization of strike and dip on planar features, lithology, bedding, fractures, and vugs. When core is available, features identified on log-derived images can be correlated or calibrated to it, or when core is absent, images may serve as a substitute. Borehole images are useful in formation evaluation (when calibrated), sedimentology, stratigraphy, and structural analysis. Current applications include core orientation, 'reconstructing' missing core, identification and characterization of fractures and depositional features (e.g. bedforms), reservoir architecture, bedding, grain size, porosity, permeability, net sand and net pay counts, faults, folds, and fractures (hydrocarbon, water, geothermal wells, and in rock engineering), evaluation of borehole stress (borehole stability), directional placement of wellbore for optima...
Current downhole video systems have successfully been used during the multilateral completion process. The technology is specifically being applied to the testing, inspection, and evaluation of multilateral junctions. Some examples are presented, complete with video footage from different stages in the process of building a multilateral junction. Downhole video field data is also presented demonstrating cases of properly milled casing windows, malfunctioning whipstock equipment, and a casing window inadvertently drilled in an unconsolidated formation. Introduction Confidence in the mechanical integrity of a multilateral junction can be greatly increased with downhole visual examination. Downhole video technology can be used to increase the economic attractiveness of multilateral completion methods by decreasing the risks involved with unknown multilateral junction integrity. It can also provide unique diagnostic information during the drilling and completion to more efficiently complete wells utilizing multilateral technology. Multilateral Technology Background Multilateral completion technology is being used more in recent times due to the positive experiences gained in improving the economics of producing oil and gas in some areas and situations. This technology makes economic sense by reducing the number of platform slots required offshore, reducing cuttings and mud disposal costs, reducing drilling time, increasing zone exposure, and increasing recoverable reserves. Multilateral completions have been classified into four types, or levels, of increasing technical difficulty and expense. - Level 1 is the simple open hole completion type.–Level 2 is a cased bore re-entry with an open-hole lateral or a liner hung in the lateral.–Level 3 is a cased trunk and lateral joined mechanically, but having no pressure seal.–Level 4 multilateral completions have both mechanical and pressure integrity at the junction. As the technical difficulty and investment in rig time and equipment increases, it becomes increasingly important to verify the results and to be able to quickly solve any problems that may arise during the installation. This is especially true of the Level 4 type multilateral junction. Considerable effort is made to establish the pressure seal in these completions, and verification of that seal is important. Downhole Video Technology Background The first camera patents related to borehole imaging date from the 1950s. By the 1970s downhole video cameras were commercially used in shallow water wells. This downhole imaging proved to be very helpful and the technology became commonplace in the water well industry in the late 1970s and continues to this day. By the 1980s, downhole video technology had advanced to the point where it began to be utilized in some shallow, low pressure segments of the oil and gas industry. Some imaging systems did not provide video, but only provided a still image, updated after a period of several seconds. These had limited use regarding inflow characterization, due to the lack of image movement. Today, state of the art downhole video systems provide high resolution, full motion, real-time, interactive visual examination of downhole equipment, conditions, and fluid flows at the depths and pressures needed for them to be useful during multilateral completion operations. P. 517^
This paper was prepared for presentation at the 1998 SPE India Oil and Gas Conference and Exhibition held in New Delhi, India, 7–9 April 1998.
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