New downhole components meet needs for extreme high temperatures

HT wells are hardly a new phenomenon in the oil field, and the oil and gas industry has kept pace with the challenge by developing downhole tools that can withstand the impact of extreme conditions. As operators push into deeper, harsher, and more complex reservoirs to produce oil and gas, temperatures are rising, so much so that HT environments are impacting the ability of directional drilling and logging tools to provide critical downhole data to ensure safe, reliable, and efficient drilling. To take industry to the next level, new-generation downhole tools are designed to function reliably in extreme HT environments.

FIGURE 1. Life expectancy has increased as plastic-encapsulated electronics on a plastic board (left) have evolved to ceramic-encapsulated electronics on a plastic board (right) and ceramic and metal components with no plastic. (Images courtesy of Schlumberger)

As drilling has become more challenging, companies have come to rely on sophisticated LWD and directional drilling tools that continuously measure and transmit critical information from downhole to the surface in real time while steering the well to the desired target reservoir. Today the components – electronics, sensors, elastomers, and seals – required for these tools typically can withstand temperatures up to 175°C (350°F), which is important when considering that reliability decreases greatly with temperature increases and exposure time.

Extending HP/HT applications

Schlumberger deployed a multifunctional LWD service along with a formation-pressure-while-drilling service for an exploration well in Norway where the reservoir temperature exceeded 175°C. Key to the success of the operation was that the selected technology functioned without battery power. Since a battery is often impacted by high temperatures, the power had to be provided by a down-hole turbine/alternator located in the MWD tool. The tool was able to acquire the real-time information the operator needed to make the correct decisions to drill the well successfully.

Temperatures in new producing regions increasingly are reaching well above the 175°C threshold of downhole tools currently available to the industry. Commercially available downhole tool components cannot withstand these temperatures in the while-drilling application. Operators often have to drill HT wells without the benefit of LWD technology, relying instead on rotary equipment to reach total depth (TD). That limitation poses the risk of well collisions, reduction of real-time data to mitigate the risk of kicks and losses, and missing targets, along with the need to confirm final well positioning with a subsequent wireline run.

Industry forecasts indicate that the need for high-level HT and HP/HT services will continue to increase. With that challenge at hand, Schlumberger is developing next-generation LWD and directional drilling technologies that will allow customers to drill in reservoirs with temperatures beyond 175°C – environments where existing down-hole technology is no longer applicable.

HP/HT challenges

Extremely high temperatures pose a number of challenges for downhole tool components such as sensors used for directional inclination and gamma-ray measurements and elastomers and seals used on downhole connections that ensure electronics are performing at the proper pressure while enabling equipment such as turbines and alternators that power LWD tools to function.

FIGURE 2. Newer components have been developed for the HT frontier.

Elastomers tend to lose their mechanical properties and crack when exposed to extremely high temperatures, causing pressure fluid to leak and further damaging the components. Extreme heat also can trigger a chemical reaction on the components that accelerates corrosion, impacting the welds. When combined with the downhole environment of shock and vibration, these problems become especially difficult to manage and ultimately lead to an increase in failure rates.

The biggest challenge involves the electronics themselves, traditionally designed as plastic-encapsulated components mounted on plastic boards that have a life expectancy of 1,000 hours at 150°C (300°F), dropping to 100 hours at 175°C. Ceramic-encapsulated components last longer at 175°C but are bigger and heavier than plastic parts.

Since space is restricted in dowhole tools, the best solution is a mix of both ceramic and plastic components. As temperatures increase, the life expectancy of the components decreases. The reliability of a system composed of plastic boards will always be linked to the plastic component.

Over the last years Schlumberger made a large investment in developing electronic components that can withstand high downhole temperatures. The company developed a proprietary ceramic electronics technology that can operate in 200°C (400°F) environments with a life expectancy that far exceeds companies’ operational needs.

After extensive testing and qualification in test facilities, these technologies have been successfully field-tested in multiple global markets where they were validated in reservoirs with temperatures in excess of 200°C. In one Southeast Asia well with a reservoir temperature above 200°C, newly designed directional inclination tools allowed an operator to drill and log the well all the way to TD in one run, resulting in considerable time savings and reduced risk from the previous drilling workflow.

Three key sectors for HT applications

Early successes in field tests indicate these new technologies will deliver an important step-change in the development of HT reservoirs worldwide, targeting three high-profile sectors for application:

• Temperatures in the North American directional land market, particularly high-volume gas development plays such as the Haynesville, which is the biggest HP/HT region, can reach as high as 185°C (365°F), which has been recorded. Improved downhole tools will allow access to reservoirs where operators either cannot drill or are forced to drill with a minimum amount of technology, which is contributing to nonproductive time, higher costs, and failures;
• The Gulf of Thailand is a region characterized by fast factory drilling to produce the high volume of gas for the supply of Asian markets. Here, reservoir static temperatures can exceed 200°C. Operators encounter bottomhole circulating temperatures higher than 175°C. Often, drillers have to pull out of the hole, lay down the LWD and directional drilling equipment, and proceed with only rotary equipment to reach TD – without the benefit of any downhole measurements to steer the well; and
• International offshore oil and gas drilling is where operators are pushing the boundaries of E&P. While this sector includes reservoirs worldwide, key locations are the North Sea, Mexico, Malaysia, Australia, Indonesia, the east coast of Africa, and the Gulf of Mexico (GoM). These areas provide a growing HP/HT market where bottomhole pressures above 30,000 psi and temperatures up to 200°C are encountered. Drilling for deep gas on the GoM shelf also is impacted by high temperatures. Wells in this sector are expensive to drill, and any lost time or failure of equipment can be catastrophic. Companies need downhole measurements to reduce risk while drilling and also want assurance that they can gain reliable downhole data in case they are unable to perform a wireline run post-drilling because of the complexity of these wells.