When inspecting oilfield surface equipment for integrity issues, the most comprehensive tool available is the combination of the human eyeball and brain. The ability to detect varying colors, textures, and features down to a submillimeter level is unsurpassed. Recording this visual inspection for records or further diagnosis by eye at the surface relies on the latest camera technology.
Video technology has evolved significantly with the advent of high-definition (HD) and 3-D cameras streamed from the helmet of an offshore worker direct to onshore for analysis and storage. Now some of the technology revolution in video technology that we all take for granted in our day-to-day lives is beginning to be deployed in the wellbore environment.
The idea of downhole cameras has been around for many years. The challenge of getting the technology in a camera phone to work at high temperatures and pressures and then transmitting the images back to the surface has meant, however, that the downhole cameras that have traditionally existed have had low functionality with poor quality – still capturing images in black and white. As a result, while occasionally useful for well integrity monitoring, these cameras were limited in their applications.
The latest downhole video technologies can now deliver full-color HD video either streamed to the surface or stored in memory, enabling the techniques applied at the surface to now be applied downhole.
Evolution of downhole video technology
Whether deployed on electric line, slickline, or coiled tubing, the latest generation of downhole video cameras can survey a complete tubing string to give an HD visual image of the tubing wall and completion hardware. Delivering these pictures to the surface requires the marriage of several leading-edge technologies.
Lighting must be provided downhole. Originally this might have been via an unreliable and inefficient filament bulb. Now cameras use LED technology that originated from a McLaren sports car. The camera lenses have to be able to sustain pressures up to 22,000 psi, minimize heat transmission, and pass the maximum light levels. The camera sensor must be able to sustain elevated temperatures for extended periods, which has been achieved using experience learned from the defense and space industries.
Once the image is captured, the data quantities far exceed those normally found in downhole sensors. The downloaded HD movie may be 15 gigabytes; a three-hour downhole video of a completion will be no different. This data can either be stored downhole on memory chips or streamed to the surface. The technology of large-volume high-speed memory chips that can work in well-bore temperatures is still developing. If the images are to be streamed in real time to the surface, traditional electric line systems will only run up to 100 kilobytes (kb)/sec,
which is insufficient for video. High-speed telemetries that will work at speeds greater than 200 kb/sec must be used and combined with the latest in video compression technologies to provide 24-frame/sec color video. Without any one of these key technologies, the video camera will not be able to deliver images of sufficient quality for anything more than basic well integrity work.
Downhole video applications
Basic well integrity work – where the camera is used to image a single wellbore feature – is, however, still a growing application for downhole video technology. Electric-line cameras will have both downview and sideview cameras. The side-view camera can be rotated as required via a motor controlled from the surface.
The advent of full 24-frame/sec downhole video allows the use of camera technology for leak detection. Figure 1 is from a well in which a company was unable to get down due to an unknown obstruction. To ensure that the company got good images in the zone of interest, the well was bullheaded with nitrogen. While running in the well, the camera suddenly captured a previously unknown leak where fluid from the annulus was entering the well. The still image from the video also shows that wells do have color in them, particularly where there is corrosion or damage.
In another case a company knew that it had communication between the tubing and A annulus and that the leak was relatively close to the surface. The oil well was bullheaded with weighted brine, and the A annulus was pressurized with nitrogen. The electric-line video camera, which was capable of streaming live video, was then run in the well to locate the leak. Figure 2 is a snapshot from the sideview camera where bubbles forming at the tubing joint are visible. The flow rate was so low that this leak would not have been detected by most other means.
Cameras also can be combined with other tools such as calipers in a single tool string. The qualitative camera complements the qualitative caliper. In Figure 3, the marks left by the 24-arm caliper run can be clearly seen, along with corrosion pitting on the tubing wall. Only one or two of the caliper arms will be picking up the pitting, and even then the vertical resolution may not be sufficient to obtain a good evaluation of the problem. The camera clearly shows the state of the tubing but cannot measure the depth of the pitting.
Legacy of downhole cameras
Twenty years is often said to be the time it takes for a technology to realize its potential in the oil and gas industry. Downhole camera technology is now reaching that age. Using developments from the media, telecommunications, defense, and space industries, this technology is finally delivering quality visual images that can help operators around the world improve safety, reduce risk, and eliminate uncertainty.