Patent Application
20220205964
The following is a tabulation of some prior art that presently appears relevant:
This invention relates generally to a system and method for autonomously detecting, quantifying, and automatically reporting CH4 leaks to the atmosphere. The invention relates more specifically to a system and method that uploads data autonomously to a central server from one or more CH4 sensor devices located on the fence line around a CH4 source, each device consisting of a CH4 sensor corrected for cross-sensitivities to interfering gases and ambient temperature for improved CH4 leak detection, quantification, and geolocation and reporting, said system being capable of off-grid operation by means of solar, wind, or some other renewable energy source that charges an on-board battery.
A specific need exists for autonomous and accurate detection, quantification, and automatic reporting of CH4 emissions (“leaks”) to the atmosphere. CH4 is flammable, contributes to background ozone pollution, is a potent greenhouse gas, and is a valuable commodity.
Continuous CH4 monitoring is increasingly needed to reduce the risk of flammable leaks, identify and address sources of pollutant and greenhouse gas emissions, and to reduce saleable product losses. CH4 emissions to the atmosphere come from a variety of natural and human sources, and national and international policies to identify and reduce these emissions is of increasing priority. Oil and gas production areas are a significant source of CH4 to the atmosphere, but the location, timing, and magnitude of CH4 emissions are often poorly quantified. A typical oil and gas production basin can encompass hundreds of square miles, with hundreds of thousands of potential CH4 emission sources from the tens of thousands of well pad, gathering, and transmission facilities within a typical basin. Similarly, large concentrated animal feeding operations (CAFOs) can consist of tens of thousands of livestock, multiple sewage lagoons, large manure storage piles, and other sources of CH4 emissions to the atmosphere. Finding and mitigating CH4 emissions at their source has the potential to reduce economic losses, improve air quality, and minimize the climate impacts of the energy production and agricultural practices needed to power and feed a growing global population. Thus, inexpensive, unattended, and autonomous monitoring systems are required to provide a robust and economically feasible continuous CH4 emissions monitoring solution suitable for extensive field deployment and operation.
Many commercially available research-grade CH4 detectors, e.g., the Picarro model G2301 or Los Gatos model 915-0001, are optimized for ambient atmospheric measurements at ultra-trace levels well away from source regions. These detectors offer extremely high sensitivity, high selectivity for CH4, and high instrument stability over time, but can require skilled operators, typically consume tens to hundreds of watts of AC power, and cost tens of thousands of dollars or more for each detector. These research-grade detectors are cost-prohibitive for use in a continuous emissions monitoring network set up to detect, quantify, and specifically attribute methane leaks to individual sites among thousands of well pads in an oil and gas production region, or at the thousands of CAFOs distributed throughout the agricultural regions of the U.S. A wide range of less precise, lower-cost CH4 detectors are commercially available, for both personal exposure monitoring (e.g., the Honeywell GasAlert Extreme) and for combustible gas leak detection (e.g., the Bacharach Leakator®). These detectors are less sensitive than the research-grade detectors mentioned previously and are more prone to undesired sensitivities to gases other than CH4 which can lead to erroneous “false positives,” especially from other combustible gases such as hydrogen, ethanol, and/or carbon monoxide. Typically, these detectors are designed for a fixed installation and require AC power or are designed to be hand-carried and require frequent battery replacement. Detector costs range from hundreds of dollars to thousands of dollars. These CH4 detectors are not typically designed for long-term unattended use in remote locations without reliable AC power and do not provide telemetry of measured CH4 values to a cloud-based server. Modern microfabrication technology has enabled a new class of commercially available, miniaturized, and inexpensive CH4 sensors, typically based on metal oxide semiconductor (MOS) or electrochemical cell (ECC) detection of CH4. These sensors are compact (˜1cm3 in volume) consume very little power (tens of milliwatts) and are sufficiently inexpensive (˜$10 per unit) to enable cost-effective large-scale deployment. Drawbacks to these MOS-type sensors include significant interferences from non-target gases such as carbon monoxide (CO) and non-methane hydrocarbons (NMHCs) and an undesired sensor response from changes in environmental temperature (T) and water vapor (H2O). Without the ability to specifically measure and correct the raw sensor output for interfering gases and ambient temperature changes, these MOS or ECC sensors will suffer from false positives, i.e., spurious CH4 detection due to temperature and humidity changes or due to elevated levels of interfering chemical species. Avoiding false positives from undesired sensitivity to chemical or environmental interferences is essential to maximize the reliability of a CH4 monitoring system, to enhance cost-effectiveness of its incorporation into a large-scale leak detection and repair system, and to accurately monitor CH4 leaks from thousands of potential sources in remote areas.
The present. invention is an integrated hardware and software system that consists of one or more pole-mounted detector boxes installed at fixed locations around the perimeter of a facility to be monitored communicating with cloud-based software for data processing and information dissemination. Each detector box can be solar powered for off-grid use and has sufficient on-board battery capacity for several days of operation without charging. GPI coordinates are determined for each detector box at installation, along with coordinates for components of interest (wellheads, tanks, separators, flares, etc.) at the monitored facility. Once powered, the system continuously detects CH4 using an inexpensive, commercially available metal-oxide semiconductor (MOS) sensor. Ancillary measurements of ambient temperature and humidity are included in each detector box, and measurements of CO are optionally available in each detector box. One box at each monitored facility is equipped with an ultrasonic sensor to measure horizontal wind speed and direction. Chemical sensor voltages, ambient temperature, and relative humidity data are sampled multiple times per second and wind speed and direction data are sampled once per second. 1-minute averages and the standard deviation of the wind direction are calculated, encrypted, and transmitted every 5 minutes by an embedded microprocessor equipped with either a cellular radio or wifi radio to a cloud-based server. Software on the server applies calibrations to compensate for cross-sensitivity to temperature, humidity, and CO to convert CH4 sensor voltages into CH4 mixing ratios in parts per million (ppm), which are logged and displayed along with the ancillary data as a time series on a browser-accessible dashboard. Data are encrypted and available for download in various formats by authenticated users. Deriving and displaying CH4 leak rates, rather than just CH4 concentrations, is a crucial step that greatly enhances the information provided by a continuous monitoring system, offering a more accurate picture of actual leak size by normalizing the effects of atmospheric dispersion on concentration. The system software automatically incorporates wind speed, wind direction variability, and derived atmospheric stability parameters as input to an atmospheric plume dispersion model (e.g., van Ulden, Atmos. Environ., 1978) to calculate, log and display 15-minute-averaged CH4 leak rates as a time series plot in the dashboard. Errors in simulating atmospheric dispersion increase during periods of light and variable winds, so CH4 leak rates are not reported for wind speeds below 1 meter per second and for 15-minute-average wind direction variability in excess of ±30° .
The usefulness of a targeted LDAR program depends critically on the ability of a continuous monitoring system to reliably detect and quantify CH4 leak rates (not just CH4 concentrations), geolocate probable sources, and alert operators to any leaks that rise above some actionable threshold for a given facility. In practice this threshold can vary with facility size, operator requirements, applicable regulations, and other practical considerations. The present system alert threshold is fully user-configurable but by default sends automated text or email alerts to operators when a 4-hour running mean of CH4 leak rates in excess of 2 standard deviations above a 30-day running mean is detected at a monitored facility. Additional calculations use average wind direction and its 15-minute variability to generate an approximate upwind source footprint and automatically identify potential source locations at the monitored facility. Automated alert information transmitted to the operator includes the facility name, location, leak rate and its uncertainty, and the most probable component(s) to which the leak is attributed as a guide for LDAR team response. Leak geolocation accuracy depends on atmospheric transport conditions and improves over time, especially when leak detection by two or more detector boxes permits triangulation to a specific source location or facility component. For each 15-minute average leak rate calculation, the system also generates a .kml file depicting facility components, detector box locations, and the calculated upwind footprint for the leak to provide a visual representation in Google Earth to guide LDAR team decision making (
The present invention simultaneously measures ambient temperature (T), ambient relative humidity (RH) and optionally ambient carbon monoxide (CO) and corrects the raw CH4 sensor signal to account for these confounding factors, maximizing CH4 accuracy and reduce the incidence of “false positive” leak reports. One or more CH4 detector boxes (
The ability to remotely deploy and autonomously detect, quantify and report emissions of methane and other gases to the atmosphere is an important step in the evolution of emissions calculation and reduction. This will assist energy producers, regulators, researchers, and other interested parties to better understand the emission profiles of various locations. Unlike more traditional methods that provide an emission profile at a particular point in time and/or provide a concentration level with little or no insight into the emissions profile outside of the particular time of measurement and the actual emission rate, this system will provide a more complete emission profile by capturing emission information on a continuous basis and provide an actual estimated omission rate, including calibrations that correct for factors that can impact the emission calculation such as temperature and relative humidity. The autonomous nature of this invention further allows for the continuous monitoring of facilities to occur without the need to have personnel on-site, allowing increased levels of information related to emissions without the need to increase headcount. This invention will allow a user to automatically learn of a situation at a particular facility that is of interest and/or may require attention in near real-time rather than the more traditional approach whereby emissions may go for days, weeks, or months without being detected or addressed. Although the description above contains many specificities, these should not be construed to limit the scope of the utility of this capability but as merely providing illustrations of some of several uses.
