Real real-time drill pipe telemetry: a step-change in drilling: high speed data transmission through the drill pipe has been a long-sought goal—it's finally nearing commercial use

World Oil, Oct, 2003 by Perry A. Fischer

For over 50 years, technology has been proposed that would allow formation evaluation and borehole navigation while drilling in real-time. The savings in drilling/rig time and cost would be substantial. In 2000, Grant Prideco and Novatek formed a joint venture corporation, IntelleServ, to commercialize a high-speed drill pipe telemetry system. In 2001, US Department of Energy's National Energy Technology Laboratory (NETL) partly funded the venture. The need and uses for this technology, its design, testing and status to date are discussed herein.

BACKGROUND

For the past two decades or so, the need to improve real-time has been partially met by LWD/MWD systems that use mud-pulse telemetry to get the data to surface. This technology is limited by a data transmission rate of, at best, 10 bits per second. This severe limitation means that the data must be more sparse, decimated or summed--all of which limits resolution and eliminates certain data-intensive measurements. Retrieving the data also slows drilling operations. In addition, mud-pulse transmission cannot be used with foam- and gas-based drilling fluids.

In recent years, three technologies have emerged in an attempt to further improve downhole data transmitted in real-time: memory logging on drillstring, electromagnetic (EM) transmission, and disposable optical fiber.

Memory logging on drill-string--although comparable in resolution to electric line logging--is far from real-time, even if the memory module can be circulated to surface. It is best used in situations where electric line cannot be applied, such as deviated and difficult holes.

Another technology, EM transmission, suffers from rapid attenuation of signal. This limits it to shallow depths. Even though hanging off antennae in the drill pipe can extend its depth range, this practice is time consuming and potentially problematic. When EM's added cost is combined with its limited depth range, the technology becomes most appropriate in certain niche applications, such as shallow TVD, under-balanced extended reach wells.

Currently under development is a disposable, fiber optic telemetry system. Proposed in the early '90s at Sandia National Laboratories, the idea received initial funding and passed several testing hurdles. However, the project languished several years until 1999, when GTI and a major service company took an interest in the project. GTI acquired the patent and partnered with Sandia Corp.

The lightly-protected, inexpensive fiber runs the length of drill pipe, from the BHA to surface, and is capable of transmission rates in the 1 million bits per second range. The fiber can be circulated downhole from a surface spool, as well as reverse circulated up from the BHA. For the latter, a special downhole fiber-spool/sub assembly, 10-ft long and weighing less than 100 lb, is being tested. Several hurdles have been overcome and field tests have demonstrated proof-of-concept. Most important, the two greatest concerns--abrasion and breakage of the fiber due to circulation pressures--turned out not to be serious problems. The current effort has focused on temporary deployment of the fiber as the bit nears the zone of interest, rather than continuous deployment from spud of the well. The project has been licensed to a major service company, with commercialization hoped for within two years.

At least 10 patents have been issued during the last 50 years in attempts to create drill pipe telemetry, using both hardwired and induction-based transmission across connections, but none of these have neared commercialization. Like all hard-wired jointed systems thus far, the electric contacts at the drill pipe joints proved too difficult to reliably align, allow perfect contact, and not leak under field conditions. Induction across couplings has a host of problems, most notably signal/field losses and the need for downhole signal-boosting.

In 1997, NETL funded a research and development firm, Novatek, in Provo, Utah, to develop another long-sought goal: a reliable, long-lasting, mud-driven, steerable, percussion drillbit system. Ideally, a high-speed real-time feedback was required for the system, but such systems were unavailable. The company realized that solving the feedback problem was at least as big a project as the percussion drillbit.

Enter Grant Prideco, the world's leading drill pipe manufacturer. Its expertise in drill pipe and coupling design, together with its downhole know-how and marketing abilities, made it the perfect match with Novatek's research. In 2000, the companies formed a joint venture, IntelleServ, with the goal of commercializing a high-speed drill pipe telemetry system. In 2001, NETL partly funded the venture.

THE SYSTEM

It was realized early on that hard-wired drill couplings, no matter how well designed, would probably always be prone to failure as the number of connections and the many connect/disconnect cycles grew. Therefore, induction was chosen as the means to transmit data from joint to joint. This, however, carried with it many problems to overcome.