Development Of An Electro-Opto Logging Cable And Video System For Offshore And Other Downhole Applications
Authors: Peters C.A. , Schultz P.K. , Cobb C.C. 
Published: October 2008

Over the years, oil and gas well operators have been able to develop solutions to practically all problems that occur downhole. The difficulties and expense incurred in the implementation of these solutions, however, can be significantly multiplied when the problem is incorrectly identified. Before the development of real-time downhole video systems, identification of downhole problems usually involved interpretation of well performance with electronically-collected data, or in some cases, the use of lead impression blocks. Misinterpretation of data often resulted in unsuccessful repair operations. Real-time downhole video eliminated many of the problems by allowing the operator to view actual downhole conditions in real time and accurately identify problems. However, operational difficulties experienced with earlier systems that employed coaxial cable prevented widespread usage of the systems.

This paper will describe the development of a small-diameter electro-opto cable for downhole video use that overcomes many of the operational limitations experienced with earlier cable designs. The discussion traces the cable through several iterations of development to its final form. The broadened scope of downhole video service applications that have resulted from the development of a state-of-the-art small-diameter electro-opto cable and other camera enhancements will also be presented.

The paper will conclude with three case histories of successful video logging jobs made possible by the small diameter cable and enhanced equipment capabilities.

Introduction

Before development of small-diameter electro-opto logging cable, real-time downhole video (DHV) systems relied upon specialized, large-diameter (9/16- inch [14.3 mm]) coaxial cable to transmit the high frequencies required for real-time video when logging in wells of significant depth.' Because of operational difficulty in maintaining pressure control with the large-diameter cables, coaxial systems were primarily used in wells with little or no surface pressure. The difficulties typically experienced when operating large-diameter cable against high pressure are illustrated in Table 1.

Although small-diameter coaxial cable may be used in deep, high pressure DHV applications, its limited bandwidth prevents use with a real time system. If small-diameter coaxial cable is needed because of high pressure and extended viewing depths, a less demanding "video" system that provides a series of still pictures must be chosen. Experience has shown that the superior information provided by a real-time video image is worth the effort to overcome the drawbacks of using large-diameter cable. The increasing need to log or service wells under high- -pressure conditions provided the stimulus for initiating developmental efforts for a small-diameter electro-opto logging cable that could not only facilitate use of real-time DHV in high-pressure conditions but also could be used for production logging-type operations.

The final development of the small diameter fiber-optic cable provided many enhancements to DHV technology. Video quality was improved considerably, and more importantly, the reduction of the cable diameter broadened the scope of downhole video usage. The 7/32-inch [5.6 mm]-diameter electro-opto cable is capable of routine operation in high surface pressure environments.