Before using downhole video to image a well, it is important to understand the limitations or disadvantages of the system. Limitations include well preparation, cost, and the inability to piggyback the system with other logging tools.
The largest limitation or obstacle to successful imaging is the effort required to prepare the well. In many cases, the wellbore fluids are too opaque to obtain a clear image. If the produced fluids are to opaque to provide a clear image, then additional effort is required to obtain a clear image. In some cases, letting the well stand idle for a period of time can lead to a separation of fluid and yield clear images once the camera reaches the base of the oil pad. However, the impact on costs due to lost production or downtime must be considered. In Coalinga, wells that had been idle for a period of one to two weeks were found to be clean enough for unassisted imaging. However, in most cases, it was necessary to pump fluid down open-ended tubing placed just above the static fluid column. This required the services of a pump truck and several hundred barrels of a non-damaging fluid, usually a 2% NH4CL or 3% KCL solution. Each well usually required 200-300 barrels of fluid pumped at a rate of 2-4 bbl/minute to clean the fluid column up enough for clear video imaging. Thus in order to image the entire well, two runs were required. The first trip consisted of a run down the annulus between the tubing and casing to the point just above the fluid level, and a second run through the tubing with clean fluid being pumped downhole at the same time.
Another limitation to downhole video technology is the cost. A random survey of video logging costs between various geographical areas found a tremendous range of rates that did not follow any set pattern of cost per foot, etc. Thus it is important to check with other operators within the region as well as outside the region to determine a fair price. Another cost factor is the actual cost of the tool. Care should be considered when running a camera in a hostile environment, especially when less expensive, mechanical tools are available. As always, this requires special consideration of the value of information.
A final disadvantage of the tool is its limitation to the field of vision and the inability to piggyback other logging tools with the system. Thus any attempts to gain data beyond the wellbore required multiple logging runs. However, several companies are working on combining the downhole video camera with a suite of production logs including spinners, tracer tools and even gamma and neutron tools. When introduced on a regular basis, this will make the downhole video/combo tool the preferred method of production logging.