Cable Adapter For High-Temperature And High-Pressure Problems In The German Ultra Deep Ktb Well
Authors: Greger Bernd , Kessels Winfried , Zoth Gustav 
Published: October 2008

High temperature techniques and high pressure tools are increasingly demanded in exploration or production works. Scientific or maintenance measurements in deep wells or hydro?/geothermal vents require telemetry systems that continue operation even at elevated temperatures or maximum stresses. In the course of the KTB-project a pressure-tight, detachable coupling for a flexible and armored, multiple conductor mineral-insulated cable has been developed by using new materials such as glass or ceramic compounds as well as high-tech manufacturing technologies like laser welding or orbital TIG welding. This connector is designed as data conducting high temperature/high pressure interface between any sensing device and MI-cables as well as a universal connection between MI-cables and all standard logging cables and it will be employed at the ultimate sections of the KTB well. Several components and two entire prototypes of this development have been thoroughly tested at various test facilities up to operational conditions of 1500 bar and 300° C simultaneously. Results verify that the design, which is described, meets severe safety requirements and prove its suitability for hostile environments.

Introduction

As part of an international project for world-wide lithosphere exploration, the German government is funding the continental deep drilling program (KTB). The project started with drilling into crystalline rock in 1987 near Windisch- Eschenbach (North Bavaria, Germany) and it is planned to achieve a final depth of 10.000 m in 1994 [1]. Temperatures in the range of 300°C and simultaneously pressures above 1.100 bar are expected, Among others, scientific results should yield information about the formation, growth and presence of raw material deposits.

However, the project is also technically of special interest, as new technologies for drilling and sensing have to be developed that comply with these extreme and hostile environmental conditions. One of these new developments which have become necessary because of severe conditions at the lower end of the well are special means to conduct logging data from the high temperature sensors at the very bottom up to colder zones where standard equipment is employable, This interface between any sensor head and conventional logging cables - a special coupling device with a heat resistant cable - was the subject of a separate development and is presented hereafter.

Schedule and Organisation

The development of this coupling device has been commissioned by the KTB project management to THETIS Technology GmbH Hanover in 1991 because THETIS was experienced in purpose-built deep sea/high pressure equipment.

Work started with a problem definition phase and a feasibility investigation to detect various conceivable alternatives. Pretests to determine certain mater-i al configurations and welding procedures were followed by the design phase for a first prototype. Next to manufacturing, which ended in January, 1993, an intensive testing program started to experience all components systematically under operational conditions.