Wireline logging tools, widely used for oil and gas exploration, are used to monitor downhole formation conditions, such as pressure, temperature, electrical resistance, density, viscosity and porosity from water- or oil-muds filled wellbores. These tools are integrated with electrical feedthroughs, interconnectors, connectors, bulkheads and other electrical component packages for power, data and signal transmissions. They must be highly reliable when exposed to harsh environmental conditions; if not, component failures can lead to unplanned interruption of normal oil field operations and loss of revenue.

Figure 1. HSG High-Tg sealing material (XTS) based electrical component packages for downhole and geothermal logging tool integrations. Source: HSGFigure 1. HSG High-Tg sealing material (XTS) based electrical component packages for downhole and geothermal logging tool integrations. Source: HSG

Successfully employing electronic equipment and electrical component packages in downhole logging and drilling services and operations mean overcoming several challenges. Qnnect (formally Hermetic Solutions Group), a worldwide manufacturer of electronic enclosures and interconnects for harsh environments, has developed various ultra-high temperature and high-pressure electrical component packages (US Patent 9,966,169, 2018) that outperform all other electrical feedthrough and connector component packages currently used in the oil and gas exploration industry.

New trends require survival in harsher environments

Downhole wireline logging requires the placement of electronic equipment thousands of feet below Earth’s surface in the vicinity of the drill bit, as shown in Figure 2. The integrated electrical feedthroughs, connectors and interconnects perform a critical role in transmitting electrical power to electronic sensors, circuits and equipment, which send and receive a variety of well formation logging data and signals from the bottom hole to a surface data processing center. Traditionally, several logging tools may be used, including:

  • Seismic profile tools for measuring the distribution of seismic fields
  • Electrical resistivity logging tools for measuring the vertical electric resistance variation
  • Distributed temperature logging tools for mapping thermal variations along a drilling well
  • Nuclear logging tools for detecting the presence of unstable isotopes in the vicinity of a wellbore; penetrating capability of the particles and photons permits their detection through casing and annular materials
  • Gamma ray logging for identifying lithology and stratigraphic correlation to provide a record of total gamma radiation detected

Figure 2. Downhole wireline logging for formation characterization and accurate assessments of an oil and gas reservoir. Source: HSGFigure 2. Downhole wireline logging for formation characterization and accurate assessments of an oil and gas reservoir. Source: HSG

More recently, many other logging tools developed by Halliburton, Schlumberger and Baker Hughes have been developed, making it possible for full reservoir characterization and more accurate reserve assessments. For example, an ultrasonic imaging service can provide high resolution images in oil- and water-based muds, showing fractures and geological features. The deployed electrical feedthroughs or interconnectors used on these instruments must not only transmit high-quality, low-noise data, but also transmit high-resolution images to the surface data processing center while withstanding harsh environmental conditions including the following:


Current legacy electronic packaging materials and data logging tools can withstand temperatures of up to 150° C for long-term field deployments of up to 10 to 20 years, or 200° C to 260° C for short-term logging services over a few hours or days. Other downhole and geothermal wellbores, located in harder sub-formations (igneous or metamorphic versus sedimentary for oil and gas), have reported temperatures greater than 200° C, and a few reported temperatures in excess of 370° C. As oil and gas industry energy exploration transitions from on-shore to off-shore and from low-temperature downhole to geothermal wellbores, wireline logging tools must be capable of routinely withstanding high temperatures, sometimes over 200° C. This presents a significant challenge for material selection and package design practice on any electrical feedthroughs, interconnectors, connectors and bulkheads that have to be integrated with any wireline logging tools. On one hand, an optimal electrical component package design must ensure that thermo-mechanical stresses are below the maximum allowable tensile and compression strengths at maximum operating temperatures for the metal header, sealing glass and pin material. On the other hand, the glass transition temperature (Tg) of the sealing glass material must withstand at least greater than the maximum downhole temperature to avoid sealing material induced failure mode.


The steady-state hydraulic pressure in most downhole and geothermal wellbores may vary from 15,000 psi to 25,000 psi (15 ksi to 25 ksi), but peak dynamic pressure variations may reach as high as 40 ksi with frequencies of 1 kHz to 10 kHz. A wireline logging tool deployed at the bottom of a hole can be subjected to lithostatic, fracture and hydrostatic pressures. While the hydraulic pressures are generally proportional to the depth of the wellbore, they can vary widely depending on the wellbore fluid density and wellbore depth. Increased logging or drilling depths from the conventional 3,000 m to over 10,000 m require wireline logging tools, integrated electrical feedthroughs and connectors to withstand higher hydraulic pressures. This exemplifies the importance of the electrical component package design, ensuring that thermo-mechanical stresses remain below the maximum tensile and compression strengths at maximum operating temperatures for the metal header, sealing glass and pin material.


Wireline logging tools are commonly operated either in water-mud or oil-mud based fluids that may include salt water or brine, sour gases (carbon dioxide or hydrogen sulfide) or alkaline (pH greater than 10) corrosive fluids at high temperatures and pressures. These environments can corrode logging tools, resulting in reduced lifetimes and increased logging service or drilling operation costs. To maintain a reliable long-term logging service with minimal maintenance cost, wireline logging tools with integrated electrical feedthroughs or connectors must be resistant to corrosion. The well-known specialty metals, such as Inconel, titanium and stainless steel must be used as metal header materials due to their excellent anti-corrosion performance.


Water vapor or moisture in water-mud or moisture-rich wellbores can significantly corrode the logging tool package as well as potentially result in failure of electrical insulation due to moisture ingress in the sealing material. Conventional sealing glass and thermoplastic materials are hydrophilic, making it difficult to operate such equipment under moisture-rich wellbores for long-term logging service operations. To increase the reliability of electrical component packages, the sealing glass material must be hydrophobic to maintain electrical insulation even at elevated temperatures.


Downhole wireline logging equipment, integrated electrical feedthroughs and connectors must be capable of surviving severe mechanical shock and vibration. Electrical feedthroughs and connectors that integrate glass- or ceramic-based materials with metals are especially prone to cracking under high mechanical shock and vibration. Typically, sealing glass cracks occur at the bonding interface between the sealing material and the metals — headers or pins — which may lead to loss of hermeticity and deterioration of electrical insulation by moisture ingress. Improved materials and design practices provide more robust hermetic sealing on any integrated electrical feedthroughs and connectors, making them less susceptible to severe shock and vibration during logging tool installation and operation.

The reliability of electrical feedthroughs, connectors, interconnectors and bulkheads under these harsh environmental conditions will affect the operation and reliability of wireline logging tools and their associated service costs.

Design and material challenges

New trends in oil exploration require an electrical component packaging design to reliably withstand these harsher and more hostile environments, which typically entails hermetic sealing of all electrical component packages at the factory. Hermetic sealing evacuates the atmosphere air within the enclosure and replaces it with inert atmosphere, ensuring no leaky channels by which external gases, vapors, corrosives or moisture can present.

One of the key challenges of hermetically sealed electrical component packages used for downhole wireline logging is that the harsh downhole environments may cause hermeticity failures by cracking the sealing glass or other sealing materials, resulting in moisture ingress. Moisture can cause several problems, including:

  • Condensing onto electronic components and causing corrosion
  • Penetrating the sealing material and degrading electrical insulation resistance
  • Combining with surface contamination — such as sodium or chloride — causing electrochemical reactions
  • A variety of other problems, such as electrical leakage, arcing or short-circuiting and contamination or fogging of electro-optical devices

Sealing materials are especially prone to failure in downhole electronic component packages. When sealing glass materials are used for electrical insulation, the bonds between the metal and glass materials may fail because the sealing glass has a relatively low glass transition temperature (Tg). For example, thermoplastic polyetheretherketone-based material (PEEK) has a glass transition temperature of approximately 145° C. Downhole temperatures greater than 150° C may cause deteriorated reliability and even failed logging or drilling operations.

Thermal expansion coefficients among electrical components must also be compatible. An electronic component package, such as a feedthrough or connector consists of three sub-components: a metal header, a glass-based seal and one or more metal pins — each material having different coefficients of thermal expansion. As a result, when the electronic component package is exposed to high temperatures, high differential thermal stresses could develop at interfaces between these components, leading to mechanical failure if thermo-mechanical stresses exceed the material’s maximum allowable tensile or compression strength. These stresses can be exacerbated when they occur in the presence of high hydraulic pressures and dynamic or vibration environments during logging tool installation and operation.

High-Tg sealing and hydrophobic sealing material sealed electrical component packages

Qnnect (formally Hermetic Solutions Group), a worldwide manufacturer of electronic housings and enclosures for harsh environments, has developed ultra-high temperature (200° C to 400° C) and high pressure (30 ksi to 100 ksi) electrical component packages that exceed the performance of all other electrical feedthrough or connector packages in the oil, gas and energy exploration industries. This was accomplished by leveraging the development of hydrophobic sealing material with glass transition temperatures (Tg) greater than 400° C (US Patents 10,291,008 and 10,483,745, 2019). These materials include high glass transition temperature borosilicate and bismuth-boron-silica (XTS) sealing glasses, and Inconel, hastelloy, and stainless-steel pin, header and shell materials that can resist corrosive fluids and withstand high temperature and high-pressure environments. Table 1 highlights some of the unique mechanical properties of these materials.

Table 1. Hermetic Solutions sealing materials. Source: HSGTable 1. Hermetic Solutions sealing materials. Source: HSG

The high mechanical and electrical strengths, water-repelling properties and high glass transition temperatures of the Qnnect (formally Hermetic Solutions Group) sealing materials enable the sealed packages to reliably operate in high pressure environments up to 100 ksi, and high temperature environments ranging from 200° C to 400° C. The water-repelling properties of these insulating materials could provide a significant advantage over existing hydrophilic sealing glass for moisture-rich wellbore logging and exploration. The electronic component packages shown in Figure 1 are available in several different configurations and suitable for a wide range of applications.

By leveraging high-Tg sealing material (XTS) and its hydrophobicity, an electrical feedthrough or connector’s performance design can be extended at temperatures greater than 150° C and pressures greater than 25 ksi. As shown in Figure 3, an XTS glass sealed non-magnetic and anti-corrosion stainless steel and gold plated BeCu pin electrical feedthrough offers up to 30 amps of current capacity, and can withstand pressures up to 50 ksi and temperatures up to 300° C. Such performance characteristics will satisfy the most stringent requirements for current and future high-pressure and high-temperature downhole and geothermal wellbore logging applications.

Figure 3. Maximum allowed pressures at different temperatures from an XTS glass sealed non-magnetic and anti-corrosion 316L stainless steel and gold plated BeCu pin assembly. Source: HSGFigure 3. Maximum allowed pressures at different temperatures from an XTS glass sealed non-magnetic and anti-corrosion 316L stainless steel and gold plated BeCu pin assembly. Source: HSG


Qnnect (formally Hermetic Solutions Group) is a global developer and manufacturer of electronics packages for harsh environments in the oil exploration, aerospace, defense, power, energy, telecom, optical and medical industries. The company is headquartered in Painesville, OH, and has over 350,000 sq ft of manufacturing space in 11 locations across the United States, Canada and the U.K. Its dedicated engineering staff provides value-added services, including prototype development and validation, testing, device assembly, laser hermetic sealing, final packaging and sterilization. Qnnect & its family of companies’ products adhere to strict quality control certifications, including NadCap, ISO9001:2008, AS9001/C and ISO 13485. More information about Qnnect products and capabilities can be found on the company website.