A Real-Time Fiber Optic Downhole Video System

Abstract

ABSTRACT This paper provides a brief historic look at downhole video in the petroleum industry, including early tool designs, configurations, and uses. Evolving technological improvements are addressed, including fiber optic telemetry. Advantages of recent innovations are covered. A review of the varied uses of downhole video, such as wel1 tubular inspection, viewing natural gas and oil production, and assisting in fishing operations is presented. INTRODUCTION Without the ability to see downhole, alternate methods of determining downhole conditions have been developed. However, as with any task, working blind can make what might otherwise be routine very difficult. Misinterpretationsor perceptions can lead to poor decisions and disastrous results. After spending even a short period of time trying to solve downhole problems, it has most likely been heard, thought, or said, "if we could only see downhole." The first downhole cameras were used primarily in shallow water wells in the 1970's. Having vision downhole proved to be very helpful, hence the use of cameras in the water well industry became common place. Naturally the desire to work in deeper environments followed. Of course this desire brought with it many problems. Telemetry, high pressure and temperature, functional OCU1ar material, lighting, opaque fluids and condensation have been among the most difficult problems to overcome. Over time much progress has been made. Advances in the development of video equipment combined with oilfield technology have produced downhole video cameras capable of working in the extreme environments routinely found in oil and gas wells. However, the large diameter of thecoaxial cable required to handle the high data rates needed to transmit a real-time video signal has been a persistent problem when working in wells with surface pressure. Recent innovations include the development of a fiber optic downhole video system anda 7/32 in. fiber optic logging cable. The benefits of this new fiber optic system include a cable diameter reduction of 55% with a transmitting range in excess of 20,000 feet. In addition, the superior signal transmission quality of fiber optics over conventional transmission means provides much sharper resolution. SYSTEM DEVELOPMENT The earliest downhole video systems used in the petroleum industry were modified water well systems. There were many limitations, resolution or picture quality was modest, and the frequency of equipment failure was considerable. However, the images of downhole conditions that were recorded were not available through any other means. Real time viewing of natural fractures, gas and oil production, fluid flows while injecting, casing failures, leaks, and downhole fish was finally available. The results were intriguing. A plan to design and build a downhole video system specifically designed to operate in an oil and gas well environment was developed in the early 1980's. One of the first oil field downhole video systems had a target depth of 10,000 feet, a 2-1/4 in. overall diameter, which was small enough to traverse 2-7/8 in. tubing, and a maximum working pressure of 5,000 psi.