Final Report: Fiber Optic Distributed Chemical Sensors for Environmental Impact Monitoring in Carbon Sequestration

EPA Contract Number: EPD12022
Title: Fiber Optic Distributed Chemical Sensors for Environmental Impact Monitoring in Carbon Sequestration
Investigators: Alonso, Jesus Delgado
Small Business: Intelligent Optical Systems Inc.
EPA Contact: Manager, SBIR Program
Phase: I
Project Period: March 1, 2012 through August 31, 2012
Project Amount: $79,993
RFA: Small Business Innovation Research (SBIR) - Phase I (2012) RFA Text |  Recipients Lists
Research Category: Small Business Innovation Research (SBIR) , SBIR - Greenhouse Gases

Description:

Reliable gas monitoring, verification and accounting (MVA) is important to making carbon capture, utilization and storage (CCUS) safe and acceptable. There is currently a need for cost-effective monitoring techniques that can cover large areas, operate stand-alone or remotely for several years, and detect gas leaks in the subsurface, both in the vadose zone and in aquifers. Intelligent Optical Systems (IOS) proposed to develop fiber optic distributed sensors for the in situ detection of gas leaks in the geological storage of carbon dioxide (CO2) and to quantify their impact on aquifers. The proposed system incorporates fiber optic sensors in which the entire length of an optical fiber is a chemical sensor, enabling the system to cover large areas. The system incorporates pH and dissolved carbon dioxide sensors, which enable the measurement of key parameters for the detection of CO2 leaks reaching groundwater, and for the quantification of the leak impact on water resources. In addition, sensors for detecting CO2 and H2S in the vadose zone were incorporated, providing the system with unique monitoring characteristics, in particular for injection projects using CO2 streams containing significant quantities of hydrogen sulfide. The feasibility of developing a distributed CO2 sensor was demonstrated previously in an earlier project; in this Phase I project, IOS demonstrated the feasibility of developing pH and H2S fiber optic distributed sensors for leak detection in CCUS.

Summary/Accomplishments (Outputs/Outcomes):

In each of IOS' sensor fibers, a silica glass core is manufactured with a cladding comprised of polymers containing a small percentage of a colorimetric indicator. The indicator changes color in the presence of a specific chemical (H2S or pH). Upon exposure of any segment of the fiber, the analyte to be detected diffuses into the cladding and reacts with the indicator, causing the cladding to change color. The evanescent field of light reflected at the core/cladding interface interacts with the cladding, so chemical exposure anywhere along the fiber dramatically affects the spectrum and intensity of the light it transmits, which allows the quantification of the target chemical parameter (H2S or pH).
 
In this Phase I project, novel colorimetric-based sensor materials for pH were developed by polymerizing polyhedral oligomeric silsesquioxanes (POSS-derivatives). These pH-sensitive materials exhibited a measurement range between pH 4 and pH 8, with resolution of 0.02 pH (at pH 6), and a response time < 2 minutes (t90, from pH 6 to pH 7), which are excellent characteristics for groundwater monitoring. IOS fabricated fiber optic sensor prototypes up to 20 m long by coating bare silica core fiber with novel pH-sensitive materials and demonstrated the variation of the fiber transmittance at variable pH levels from pH 4 to pH 8.
 
Silicone-based polymers doped with a proprietary colorimetric-based chemistry specifically sensitive to H2S were developed. The optimal formulations to prepare highly-sensitive claddings for H2S were achieved by incorporating POSS nanoblocks in the base silicone polymer, which significantly increased the gas permeability, and therefore, the sensor response toward low H2S concentrations. Fiber optic sensor prototypes up to 10 m long were produced using these sensitive materials as claddings, and a rapid decrease in the intensity of the light transmitted by the fiber (in the 5 to 10 second range) to variable concentrations of H2S (in the 1 to 50 ppm range) was demonstrated. A limit of detection below 5 ppm was determined.

Conclusions:

IOS attended two key meetings to evaluate the commercial feasibility of the technology under development and to determine potential team members for commercialization (SPE Applied Technology Workshop "Distributed Fiber-Optic Monitoring for Well, Reservoir and Field Management" and "Carbon Storage R&D Project Review Meeting"). The IOS approach for leak detection in CCUS has raised significant interest in the distributed fiber optic monitoring community, and in companies operating in the oil industry. IOS already has initiated a dialogue with Halliburton and is pursuing a partnership for the field demonstration and commercialization of this technology.

Supplemental Keywords:

greenhouse gas, carbon dioxide, carbon sequestration, environmental impact monitoring, fiber optic, fiber optic sensor, groundwater, vadose zone monitoring, atmospheric gas, gas leakage, aquifer, SBIR