Borehole Video Camera

Basic Concept

Borehole video (or television) logging allows the in-situ depiction of visible features on the interior walls of air- or water-filled boreholes, wells, casing, pipes, tunnels, etc. This wireline method records continuous video footage of the relatively undisturbed borehole, and its real-time viewing capabilities allows tool adjustments and manipulation while logging. Video logging is time- and cost-efficient, requires little to no data processing, and often suffices as a supplement for missing core or incomplete well construction information.

Video logging can be employed to quickly survey wells, identify locations requiring more investigation, or guide the retrieval of items that have been lost in a borehole. Additionally, video logging can directly view well construction, borehole condition, lithology and lithologic features, water level, and changes in borehole water quality (e.g., precipitates, particles, gases, etc.). As such, video logging can be used to improve the interpretation of results acquired with other borehole geophysical methods (Johnson, 1993).

Theory

A video camera and light source are encased in the housing of the down-hole probe, which is suspended from coaxial cable connected to a winch. The surface-mounted components of the video-logging system include an electrically powered cable winch, control unit, television monitor, video recorder, and power supply. Probe motion, image enhancement, and camera view direction are controlled via the control unit using the monitor for visual reference.

Traditionally, a wide-angled camera lens is directed downward toward a rotational mirror that is inclined 45° to the probe axis. This allows for the simultaneous viewing of the borehole wall, which is reflected off the mirror, and a portion of the borehole below the mirror. Probes that contain articulating lenses range between closeup views of the wall and the wide-angled axial view. Often, images are composites of both views and transmitted to the surface unit throughout the log collection (Johnson, 1993).

The surface monitor displays real-time images, which allows the probe ascent/descent and camera rotation to be adjusted and the examination of features while logging. A compass and clinometer are employed during logging and used to determine the orientation of features on the borehole wall as well as the borehole itself. As such, the borehole can be viewed in greater detail and precise measurements of feature location and orientation can be collected during logging (Johnson, 1993).

Video logs contain remarkably sharp, full-color images, and the entire borehole-viewing sequence is recorded. Camera depth is determined by an encoder wheel that is turned by the cable as the probe is moved throughout the borehole. Depth values are transmitted to the control unit, superimposed on the digital images during live-stream, and stored in the recording. Video logs can be viewed immediately after logging, and data are easily transferred and analyzed (U.S. Bureau of Reclamation, 2001).

Applications

Borehole video logging allows for the direct visual examination and verification of various types of naturally occurring features. If, within the borehole, zones of poor/no core exist, video logging makes describing and correlating the missing units possible. Video logging also provides a multitude of supplemental lithologic information such as rock type, rock/mineral texture, grain size, color, and the nature of contacts, for example.

Small-scale geologic structures such as foliation, folds, faults, and solution cavities can also be identified and described. Borehole video logging allows for the observation of groundwater movement, water level, and locations of cascading water that may exist in the well. Furthermore, the description of fracture characteristics (e.g., frequency, aperture size, orientation, and borehole intersection) is easily conducted with the video-logging method.

Borehole video logging can be useful for examining borehole conditions and/or well integrity and determining the nature and degree of naturally or anthropogenically influenced alterations. Before placing casing, screens, pumps, and/or packers, video logging can be used to assess borehole wall stability. Such assessments include the identification of any fractures with broken out zones or enlargement, roughness and angularity, scoring or rifling, and cavities or voids.

Detailed inspections of casing and screen conditions are also conducted with borehole video logging. Such investigations include identifying cracks and holes, rusting, screen opening enlargements, the presence of foreign objects, or any other type of damage. Furthermore, borehole video logging can be extremely beneficial when concerned with boreholes where construction details are unknown.

To its advantage, video logging is quick, can be used in dry or submerged conditions, and often allows for narration and audio storage. However, video logging requires clear water and, therefore, may require pumping water from the borehole. Additionally, video logging requires visual review of the videos for interpretation, which can be time consuming. Older data stored on magnetic tapes can degrade, but digital images can be stored indefinitely on digital media.

Borehole video logging continues to improve with technological advances in camera electronics and data management and is an excellent tool for rapid, general, or preliminary surveys.

However, other borehole imaging techniques (e.g., Acoustic Televiewer and Optical Televiewer) are more suited to conduct complete digital maps of the borehole. Regardless, the borehole video logging method alone has aided in the following:

Quick borehole reconnaissance
Description of lithologic, structural, and hydrogeologic characteristics
Estimation of cavity or void volume
Inspection of well construction and condition
Retrieval of equipment or foreign objects in wells

Examples/Case studies

Craven, M., Carsey, F., Behar, A., Matthews, J., Brand, R., Elcheikh, A., Hall, S., and Treverrow, A., 2005, Borehole imagery of meteoric and marine ice layers in the Amery Ice Shelf, East Antarctica: Journal of Glaciology, v. 51, no. 172, p. 75-84, doi:10.3189/172756505781829511.

Abstract: A real-time video camera probe was deployed in a hot-water drilled borehole through the Amery Ice Shelf, East Antarctica, where a total ice thickness of 480 m included at least 200 m of basal marine ice. Down-looking and side-looking digital video footage showed a striking transition from white bubbly meteoric ice above to dark marine ice below, but the transition was neither microscopically sharp nor flat, indicating the uneven nature (at centimetre scale) of the ice-shelf base upstream where the marine ice first started to accrete. Marine ice features were imaged including platelet structures, cell inclusions, entrained particles, and the interface with sea water at the base. The cells are assumed to be entrained sea water, and were present throughout the lower 100-150 m of the marine ice column, becoming larger and more prevalent as the lower surface was approached until, near the base, they became channels large enough that the camera field of view could not contain them. Platelets in the marine ice at depth appeared to be as large as 1-2 cm in diameter. Particles were visible in the borehole meltwater; probably marine and mineral particles liberated by the drill, but their distribution varied with depth.

Han, Z., Wang, C., and Zhu, H., 2015, Research on Deep Joints and Lode Extension Based on Digital Borehole Camera Technology: Polish Maritime Research, v. 22, no. s1, p. 10-14, doi:10.1515/pomr-2015-0025.

Abstract: Structure characteristics of rock and orebody in deep borehole are obtained by borehole camera technology. By investigating on the joints and fissures in Shapinggou molybdenum mine, the dominant orientation of joint fissure in surrounding rock and orebody were statistically analyzed. Applying the theory of metallogeny and geostatistics, the relationship between joint fissure and lode’s extension direction is explored. The results indicate that joints in the orebody of ZK61borehole have only one dominant orientation SE126° 68°, however, the dominant orientations of joints in surrounding rock were SE118° 73°, SW225° 70° and SE122° 65°, NE79° 63°. Then a preliminary conclusion showed that the lode’s extension direction is specific and it is influenced by joints of surrounding rock. Results of other boreholes are generally agree well with the ZK61, suggesting the analysis reliably reflects the lode’s extension properties and the conclusion presents important references for deep ore prospecting.

Johnson, C.D., 1993, Use of a Borehole Color Video Camera to Identify Lithologies, Fractures, and Borehole Conditions in Bedrock Wells in the Mirror Lake Area, Grafton County, New Hampshire, in Proceedings, USGS Toxic Substances Hydrology Program Technical Meeting: Colorado Springs, Colorado, U.S. Geological Survey, p. 88-93.

Abstract: A submersible color camera was used to describe bedrock lithologies and fractures in boreholes at the U.S. Geological Survey fractured-rock research site near Mirror Lake, Grafton County, New Hampshire. From June through August 1992, video surveys were completed in 29 bedrock wells that ranged in depth from 60 to 230 meters. Use of the submersible camera was prompted by a need to verify and provide additional descriptions of rock types identified in the wells. In two of the wells from which bedrock core was collected, video images together with drill cuttings were used to determine lithologies. These lithologies corresponded to lithologies determined directly from bedrock core samples collected from two wells. For wells from which core was not obtained, video images were used to improve the interpretations of the rock types that were based only on initial logs made at the time of drilling and later detailed examinations of drill cuttings. In addition, the images were used to inspect the conditions of the borehole walls for angularity, stability, or blockage.

Li, S., Feng, X.T., Li, Z., Zhang, C., and Chen, B., 2012, Evolution of fractures in the excavation damaged zone of a deeply buried tunnel during TBM construction: International Journal of Rock Mechanics and Mining Sciences, v. 55, p. 125-138, doi:10.1016/j.ijrmms.2012.07.004.

Abstract: This paper presents results of in situ measurements of fracture evolution within the excavation damaged zone (EDZ) surrounding the tunnel boring machine (TBM) excavated headrace tunnel No. 3 of Jinping II hydropower station, China. Fractures were measured by borehole images obtained with a digital panoramic borehole camera throughout the processes of tunnel excavation and support installation. Boreholes for the digital camera were pre-drilled perpendicular to the tunnel axis from a pre-excavated branch tunnel, and a series of digital images of the borehole walls were made as the TBM passed. Digital processing revealed the lithology, pre-existing fractures and characters of rock core discing of the surrounding rock mass. Processes of fracture initiation, propagation, and closure were observed, and width, occurrence and zoning of EDZ were measured. The relationship between fracture evolution and TBM construction progress is described in detail. Based on true triaxial tests and theoretical analysis of unloading conditions of deep rock masses, the occurrence of tunnelling induced new fractures at the EDZ is discussed with respect to in situ measurement results. The results provide valuable data for EDZ analysis, future designs and the construction of deeply buried tunnels using TBM.

Norbert, S., and Katarzyna, G., 2014, Evaluating selected lithological features using photographs taken with an introscopic camera in boreholes: International Journal of Rock Mechanics and Mining Sciences, v. 72, p. 319-324, doi:10.1016/j.ijrmms.2014.09.017.

Abstract: As far as geological and mining activities are concerned, drilling protection boreholes in rocks is a frequent research and prevention practice [1,2]. The research is most often connected with the evaluation of the rock type and properties [3], and with the identiﬁcation of various discontinuities [4]. The prevention usually consists in combating the methane hazard, the rock burst hazard, and the gas and rock outburst hazard [5–8]. During research activities, the most common boreholes that are drilled are the boreholes from which cores are extracted. Studying cores allows researchers to obtain precious information as to the lithology of the rock layers. In the case of boreholes drilled for the sake of prevention [9–16], drilling boreholes with the aim of extracting cores is not justiﬁable due to economic and time efﬁciency reasons. Such boreholes can be inspected with various sorts of introscopic cameras [17]. The question is: what features of the drilled rock mass are we able to evaluate by means of the imaging methods available now, if we physically do not have the research material (i.e. the core) at our disposal? The Authors of the paper carried out research which involved visualizing the inside of a borehole with an introscopic camera [18]. The camera used all the technological developments which appeared during the last decade, and which concern the digital imaging. The parameters of the applied instrument were discussed, together with the methods of registration and the analysis of the recorded material. A careful inspection of each frame of the ﬁlm paved way for an attempt to describe selected rock features that could be registered by the camera placed inside the borehole.

Roth, M.J.S., Nyquist, J.E., Faroni, A., Henning, S., Manney, R., and Peake, J., 2004, Measuring Cave Dimensions Remotely Using Laser Pointers And A Downhole Camera, in Proceedings, 17th EEGS Symposium on the Application of Geophysics to Engineering and Environmental Problems: Colorado Springs, Colorado, European Association of Geoscientists and Engineers, doi:10.3997/2214-4609-pdb.186.POS17.

Abstract: An ongoing research program at Metzgar Fields, an athletic facility at Lafayette College in Easton, Pennsylvania, has the primary objective of improving site investigation methods for karst features using geophysical methods. Multi-electrode resistivity testing completed in 1999 located a significant anomaly at the test site and subsequent borehole drilling confirmed that a two-meter high void existed below approximately seven meters of bedrock. During the summer of 2003, we measured the dimensions of this cave using laser pointers and a downhole camera originally designed for search and rescue operations. The camera was lowered into the cave down one borehole and the laser pointers were lowered down two other boreholes. Measurements were made using triangulation; the laser pointers were adjusted so that they were aimed at the same point on the cave wall and measurements of distances and angles were taken at the surface. The cave geometry we obtained will be used in the future to make a quantitative comparison between the results of 2D and 3D resistivity testing and actual cave geometry.

Walbe, K., 1986, Utilization of the Borehole Television Camera in Conjunction With Regular Open and Cased-Hole Logging in the Devonian Shale of the Appalachian Basin, in Proceedings, SPE Annual Technical Conference and Exhibition: New Orleans, Louisiana, Society of Petroleum Engineers, 4 p., doi:10.2118/15610-MS.

Abstract: The borehole television camera has greatly assisted the identification and evaluation of potentially productive zones within the Devonian Shale within the Devonian Shale sequence within the Appalachian Basin. The application of this tool in conjunction with open hole logs has helped identify and categorize zones of natural fracturing as well as oil and gas pay zones too thin to be observed on conventional geophysical logs. The cased hole applications include casing collar and perforation inspection as well as identification of fluid and gas entries that are too small to register on conventional production logging suites. In order to give a fuller, more detailed picture of the whole well, the television information is categorized and then digitized to be portrayed in log format and at a similar scale as conventional logs.

Walbe, K., and Collart, D., 1991, Use of the Borehole Television Camera and the Low-Volume Flowmeter To Identify and Measure Gas Flow in Low-Permeability Formations, in Proceedings, Low Permeability Reservoirs Symposium: Denver, Colorado, Society of Petroleum engineers, p. 299-306, doi:10.2118/21835-MS.

Abstract: Within many of the low permeability gas reservoirs of the world identification and measurement of gas entries is difficult due to the low volume of the flow. Also, in many areas, identification of natural fracturing is important since much of this fracturing is related to better production within the low permeability formations. During logging operations the Borehole Television Camera (BHTV) is capable of giving a real-time observation of the wellbore by use of a colour television camera mounted on the end of the camera tool assembly. This camera transmits a picture directly to a monitor within the logging truck. Observed oil and gas entries are noted and natural fracturing can be observed. Also, with the BHTV's internal gyroscope the orientation of the observed fracturing can be recorded. Twin VHS videotape recorders record the logging run for a permanent client record. permanent client record. The Low Volume/High Resolution Flowmeter (HRFM) is used in conjunction with the BHTV in both open and cased hole logging as it is capable of measuring gas flow down to a fraction of an MCF. With the HRFM, flowrate is determined by injecting a tracer gas into the gas flow. The dilution of the tracer gas is then measured at a downstream detector. Mass flow is therefore determined by this method rather than the velocity of the gas in the wellbore as measured by conventional production spinner surveys. Both the BHTV and the HRFM are capable of being run in vertical and horizontal open and cased holes.

References

Morahan, T., and Dorrier, R.C., 1984, The Application of Television Borehole Logging to Ground Water Monitoring Programs: Groundwater Monitoring and Remediation, v. 4, no. 4, p. 172-175, doi:10.1111/j.1745-6592.1984.tb00909.x.

Prensky, S.E., 1999, Advances in borehole imaging technology and applications: Geological Society of London Special Publications, v. 159, p. 1-43, doi:10.1144/GSL.SP.1999.159.01.01

U.S. Bureau of Reclamation, 2001, Borehole Geophysical and Wireline Surveys, in Engineering Geology Field Manual - Second Edition: Washington D.C, U.S. Department of the Interior, Bureau of Reclamation, v. 2, p. 37-81.