Air-Drilling, Electromagnetic, MWD System Development

Abstract

Abstract Two-way communications, between sensors and other devices at the bottom of, or along, boreholes and the surface, have traditionally been performed by wirelines and stored-data technology. Telemetry (up-link) and command (down-link) functions have more recently been performed by use of real-time, mud-based methods. As more and more horizontal, slant-horizontal, arc, and other high-angle borehole are drilled (some with air), the need for non-wireline and non-mud-based communications becomes more important because of the difficulty of inserting tools and logs in the absence of a large gravitational force component, and the inability of mud-based systems to operate in air or for that matter in the absence of flow. The oilfield logging industry has developed tubing-conveyed-logging tools, but these too lack the flexibility required, because they still require a wireline. Even with side-entry subs, these tools are too costly or difficult to use in some cases. Air-drilling of directional wellbores is on the rise for a number of reasons, and wireline steering tools and mud-based MWD tools are proving to be less than effective. In recent years new wireless electromagnetic-based real-time borehole communications techniques have been developed with capabilities for supporting relatively-low data rates (compared with wireline) adequate for some applications. These are in commercial use for Measurement-While-Drilling (MWD) systems. Others are -finding their way into non-drilling use n connection with oil and gas reservoir evaluation and completion work. While most of the work has been done in larger boreholes, some systems are being built into drill-strings as small as 2.5 inches (6.35 cm) OD. Wireless electromagnetic borehole communications technology holds out hope for providing reliable, two-way, high-data-rate data and command links in wellbores; regardless of hole size and angle, mud or air, flow and no-flow. cased or open-hole. This paper traces the development of wireless electromagnetic borehole communications technology, and describes the state-of-the-art in oilfield and nonoilfield applications. Development of, and field results from, a recently completed air-drilling model are presented. Electromagnetic (EM) Borehole Communications Historically, the modern borehole communications concept was first realized using an electromagnetic method, the wireline. The wireline presented cable-handling problems in drilling. However, it did better in many cases than competitive methods of the time. When mud pulse-telemetry Measurement While Drilling (MWD) was introduced, it seemed reasonable to trade away the unused high data rate of the wireline for the convenience of the "wire-less" mud-pulse tool. Progress in the drilling industry has slowly put pressure on the MWD-services industry to improve reliability. P. 485