Wireless H2S Sensor Uses Nanotechnology To Improve Safety In Oil and Gas Facilities
Authors: Wilson Adam 
Published: February 2015

This article, written by Special Publications Editor Adam Wilson, contains highlights of paper SPE 166544, ’An Innovative Wireless H2S Sensor Based on Nanotechnology To Improve Safety In Oil and Gas Facilities,’ by Marco Piantanida, SPE, Maurizio Veneziani, and Roberto Fresca Fantoni, Eni, and William Mickelson, Oren Milgrome, Allen Sussman, Qin Zhou, Ian Ackerman, and Alex Zettl, University of California at Berkeley, prepared for the 2013 SPE Offshore Europe Oil and Gas Conference and Exhibition, Aberdeen, 3-6 September. The paper has not been peer reviewed.

Real-time monitoring of pollutant, toxic, and flammable gases is important for health and safety during petroleum-extraction and -distribution operations. Currently, many methods exist for detecting such gases, but most sensors suffer from slow response times, high power consumption, high costs, or an inability to operate in harsh conditions. This paper demonstrates a small, low-cost, low-power, highly sensitive nanomaterial-based gas sensor specifically targeted for the detection of hydrogen sulfide (H2S).

Introduction

Current personal monitors for H2S are typically electrochemical-based sensors because of their low power consumption, relatively small size, and satisfactory selectivity. However, electrochemical cells typically have fairly slow response times and are prone to degradation or errors at extreme temperatures and humidity. Semiconducting-metal-oxide (SMO) sensors have fast response times and simple interface electronics and can operate in harsh conditions, making them a mainstay of industrial monitoring. However, the power required to operate a conventional SMO sensor is typically hundreds of milliwatts. Therefore, operation of a handheld monitor using conventional SMO sensors is not feasible for long-term monitoring. To overcome this problem, the authors have fabricated very-low-power microheaters and functionalized them with tungsten oxide (WO3) nanoparticles to create an H2S sensor suitable for long-term battery-powered operation.

Description and Application of Equipment and Processes

Microheaters. Two types of microheaters are used in this research. The first is a commercially available microheater. This microheater uses a serpentine platinum heater sandwiched between a thin silicon nitride membrane on the bottom and a silicon oxide membrane on the top. Two gold electrodes provide electrical contact to the sensing layer. The second type of microheater was designed and fabricated at the University of California at Berkeley in the Center of Integrated Nanomechanical Systems. This microheater uses a suspended polysilicon bridge as the heater. The heater is isolated from the sensing layer with a thin silicon layer above and below the heater. Two platinum electrodes on top of the heater bridge provide electrical contact with the sensing layer.

Nanoparticle Functionalization. The WO3 nanoparticles used in this study were suspended in isopropanol by means of ultrasonication and deposited on the microheaters by spincasting or dropcasting.

Sensor Measurement. The WO3- nanoparticle-based microheater sensors are measured by use of a source-measure unit (SMU). One channel of the SMU is used to apply a voltage to the microheater and measure the current. The other channel is used to apply a voltage to the nanoparticle sensing layer and measure the current through the sensing layer. Data are collected with open-source instrument control software.

Gas Delivery. The sensors are exposed to a gas stream of varying analyte concentration by means of a custom-made gas-delivery system. Using mass flow controllers, the gas concentrations are diluted from a target-gas cylinder balanced in nitrogen with air, which was cleaned and dried in-line through activated-carbon filtration and pressureswing adsorption dryers before dilution with the target gas. The humidity of the gas stream is controlled by a controlled evaporator mixer. The concentration of H2S was monitored by use of a reference sensor.

Presentation of Data and Results

Nanomaterials, especially metal-oxide nanomaterials, have been inventively researched for sensing applications because of their large surface-area/volume ratios, which enhance the effect surface reactions and adsorption have on their electrical properties. Nanostructured materials also have the beneficial capability of being heated to high temperatures using very little power. Previous research has shown that WO3 nanomaterials perform well as a sensor for H2S. However, as with most metal-oxide sensors, the sensors must be heated to obtain sufficient sensitivity and response times. Therefore, the authors constructed WO3-nanoparticle-based microheater sensors for detection of H2S.