Upgrading Formation-Evaluation Electronics for High-Temperature Drilling Environments

Abstract

Technology Update Globally, increasing amounts of hydrocarbon resources are being found in fields that have very high thermal gradients. (It gets hot very quickly as you move downward.) On the drilling side, challenging, high-pressure/high-temperature (HP/HT) wells customarily have been drilled with the simplest of tools, such as turbines and mud motors, which have minimal electronics and make no measurements. Logging-while-drilling tools, which do contain electronics and require electrical power to operate, have not been used thus far in these wells. Most formation-evaluation tools have lots of electronic components, and so initially couldn’t be used in HP/HT wells. However, these wells are often located offshore, where high rig rates force operators to look for all possible means to increase drilling efficiency and optimize wellbore placement for maximum production. Meeting HT Challenges The main challenges in these environments are preventing the electronics from becoming damaged, maintaining measurement accuracy and precision, and generating or supplying the regulated power to the electronics reliably over the duration of the drilling effort. Several parallel technologies have been developed over the past 5 to 6 years that can be used on their own or in combination to address these issues. The technology developments have concentrated on three main themes: HT electronics and the operating environment, new sensor technologies and measurement methodologies to improve accuracy and precision, and active cooling. In this connection, a 2-year project to develop measurement-while-drilling tools that can record and transmit data at temperatures of 230°C—running for 14 days continuously—has been initiated by Halliburton. The purpose of this project was to finalize some of the ongoing developments in high-temperature electronics and sensor technologies and package them into a tool capable of performing in this environment. In considering the operating life of electronics, one of the main issues in HT environments is the increased rate of chemical reactions that cause the electronics to fail. In 1889, Svante Arrhenius documented the fact that chemical reactions require activation energy to proceed. The Arrhenius equation provides the quantitative relationship between temperature and the rate at which a chemical reaction occurs. This relationship is important for our industry because it governs many of the failure mechanisms for downhole electronics. The rate of chemical reactions is defined by the equation K=Ae–Ea/RT, which documents the exponential relationship between rate (K) and temperature (T). Ea is the activation energy for a particular process, and this value can be changed (by adding catalyst or inhibitor). Ae (pre-exponential factor) and R (gas constant) are empirically derived constants. Many reactions double their rate every 10°C.