Abstract
This paper describes the design, implementation, and evaluation of an environmental logging microsystem (ELM) for operation at elevated pressure and in corrosive environments, at temperatures up to 125°C. The ELM units are intended to be deployed in large quantities, allowed to collect data, and then retrieved, interrogated, and re-charged. Powered by a rechargeable battery embedded within the system, each ELM incorporates pressure and temperature sensors, control electronics, optical communication elements, and power management and battery re-charging circuits. The pressure sensor is a customized capacitive transducer chip on a sapphire substrate; details are provided in a companion paper. The electronic components and battery used in ELM are selected on the basis of functionality and form factor; packaged components are selected for ease of assembly and for added protection against the environment. The pressure sensor, electronics and battery are assembled on a flexible circuit board, folded into a stack with dimensions 7.2 mm × 6.6 mm × 6.5 mm, and encapsulated in a steel tube filled with optically transparent silicone caulk. This encapsulation provides mechanical protection against shock and abrasion, as well as chemical protection against high salinity environments, while allowing the ambient pressure and temperature to be transferred to the sensing elements. Results are reported from high-temperature and high-pressure tests reaching 125°C and 7,250 psi in brine and other corrosive environments in laboratory conditions. Field tests that were conducted in a brine well to a maximum depth of 1,235 m are also described. The recorded data were post-processed to interpret the environmental pressure and temperature.
Highlights
DOWNHOLE environmental monitoring can provide significant benefits to the petroleum and natural gas industry
The environmental logging microsystem (ELM) electronics were characterized for the consumption of static current and dynamic current, and for deployment lifetime
The encapsulated ELMs were subjected to a series of high-pressure high-temperature (HPHT) tests in a laboratory; these tests validated system performance at rated pressure and temperature limits of 50 MPa (7,250 psi) and 125°C in various ambient media, including American Petroleum Institute standard brine (API brine)
Summary
DOWNHOLE environmental monitoring can provide significant benefits to the petroleum and natural gas industry. Cross-well imaging, which is another interrogation method, is performed by propagating seismic or electromagnetic waves between boreholes to generate formation mapping [5] These techniques typically provide downhole data with high spatial resolution close to the wellbore, but limited spatial resolution in the hydraulic fractures and reservoirs. Microsystem packages for downhole applications have been reported in the recent past [26] These packages used steel shells capped by glass or sapphire, presenting rigid walls that did not allow pressure transfer into the package. The ELM system comprising the customized pressure sensor, electronics, all necessary software, battery, and polymer-filled tubular steel package serves as a versatile platform for downhole environmental sensing with high spatial resolution and large deployment range.
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