Bob Stanton explores small, rugged and fast interconnections for downhole electronic systems
High-speed, bidirectional signal and data transfer from drilling bit to and from the platform control centre is critical. Constant information control of the downhole drill bit system and sensors saves time and money as today’s systems go deeper and into hotter environments. Drill sensors are reporting temperature, pressure and direction control simultaneously with logging data taken from the material they are cutting their way through. Rapid delivery of the wireline logging information becomes critical for aiming the downhole bits and sensors in the highest value concentrations of the mud below. Noting that slurry concentration changes with temperature and underground pressure, timely information is needed at the data acquisition area above. Increases or reductions of on-line API density analysis can help direct or select key positioning of the bore well to achieve optimum quality of the crude source.
In some applications, electromagnetic telemetry is used to transmit downhole information to and from bit to surface. This is done by using a sub-surface antenna in the drill-string and another receiving system on the surface of the drill rig. The EM-wave signals are received at the surface in the data control centre. This method can assist in general position control and drive data well processes and may be used in parallel with electrical data run along the vertical wire line. Because electrical noise, such as electromagnetic interference (EMI), can cause data interruptions and limit some applications, wire-line cabling is used to protect the lower voltage and more exact data being collected by micro sensors at the bit.
The Current Generation
Today’s new sensor modules and chip technologies are being employed to offer exciting new data analysis and higher accuracy. The modules are mounted immediately behind the bit assembly and can be used to analyse on-the- fly logging information at the bit. In narrow electronic processing modules, chips and circuits monitor temperature, location and add inclination, azimuth, pressure and other physical attributes of the bit. Additionally, newer circuit chip technologies and materials with high-speed digital capabilities are being used to improve accuracy and data analysis during exploration. Gamma-ray scintillation heads built with lanthanum halide and cerium bromide survive the environment longer in elevated temperature and pressure environments. The new detection heads’ ability to develop and detect gamma absorption rates offer higher density analysis and better optical resolution of the scintillated materials at the end of the bit. This allows better boar head targeting toward the highest petroleum-based compaction within the mud area being explored.
Higher speed signalling from new sensors is processed initially on circuit boards down at the drill bit level. The lower voltage digital data produced down in the hole is then connected via nano sized connectors into the wire-line system and sent up to the surface. Nano sized connectors and cable have become critical elements in interconnecting these sensor-based monitoring systems. Benefits include their rugged performance capabilities while reducing size and being rapidly adapted in contact format and shapes to match new designs. The Nano-D connector materials and design have extensive experience in both the down-hole and military industries.
Years ago, multiple connector manufacturers worked through a military standard specification (no. 32139) that requires high reliability in areas such as shock, continuous vibration and electrical continuity. These specifications match well with the petroleum industry. Test certifications and performance under stress and extreme environments have helped protect the down-hole industry.
Nano-D connector performance provides a good example of what reliability can be achieved by a miniaturised connector. Based on a pitch of 0.635mm, these devices are only a quarter of the volume and have 80% less mass than larger Micro-D connectors. The connector’s pin and socket elements are also plated to Mil. B488-type II, Code C class 1.27. This requires a strong nickel plate barrier that is then over-plated with 50 micro inches of gold. The spring pin and socket connector system has proven reliability over wide ranges of shock, vibration and thermal changes. Made of BeCu (beryllium copper), with high tensile strength, at 17,200ksi, they easily withstand the rigors of use and abuse that is often experienced in oil and gas work. Finally, the connector pin and socket elements are crimped to high temperature, Teflon-insulated wiring that is carefully laser stripped to avoid nicking miniature wiring without the need for solder. This provides the highest thermal performance.
Nano-D connector metal shells are constructed of aluminium alloy 6061 and nickel plated to specification AMS-C-26074. Insulators are moulded of LCP per Mil. -M-24519 from Ticona E-130i that yields excellent thermal properties from -50°C to over 210°C. Connectors were initially designed with jackscrews to hold them in place. Since then, latching Nano-D connectors have been taking over and also match the mating, shock and vibration expectations needed in military and in downhole circuit use.
High-speed digital signal processing sensors used in downhole detection are more portable and expanding the demand for small light-weight cables and connectors. Ruggedised and environmentally sensitive applications fit the Nano-D family of connectors well. As mentioned earlier, logging while drilling (LWD) signal transmission is better when there is little delay getting from the bit to the controller at the surface. Designs are available that include IEEE 1394 fire-wire cable and expands on to USB 3.1 formats and CAT-6a wiring.Many of these formats support a wide range of new designs ranging from circuitry used in small military vehicles, satellite sensors and learning machinery. Higher speed data serial links can be supported with smaller size cable and rugged nano connectors. Formats from USB 3.1, PCI Express 2.0/3.0, HDMI and others reaching up to 10 Gigabit Ethernet circuits are included. Downhole logging cable designs are often required to manage noise-induced jitter and alien crosstalk from other cable in the wireline. Circuit to circuit shielding is often used in conjunction with special noise drain wires. Other noise intrusion and signal isolation can be protected with metal Nano-D connectors and special back-shells.
Design Variations
Omnetics’ Nano-D connector applications are continuing to grow and expand with a number of design variations to accommodate special applications. Their size accommodates up to 30 AWG PTFE insulated wiring and support many emerging technologies that use less than one ampere. Short run wiring and cabling will continue to be used within sensor modules down inside the bit and logging area of the bore system. Connecting modules to one another using nano sized connectors makes easy assembly and assured performance in high vibration applications. Metal shells and aluminium cable shielding is available to provide additional noise abatement and signal interruptions. Specially designed insulators will continue to evolve that include combinations of power and signal combinations are available that can include small coax, power and signals within the connector as new sensors and applications emerge.
Bob Stanton is directory of technology at Omnetics