Gas Hydrates Monitoring

BCS is assisting the Gulf of Mexico Hydrates Research Consortium and the Center for Marine Resources and Environmental Technologies (CMRET) at the University of Mississippi in their development of a multi-sensor Seafloor Observatory (diagrammed below) to be installed on the continental slope of the northern Gulf of Mexico.

As large volumes of Observatory data become available, an important requirement will be to rapidly ingest the data into a database. BCS has recently developed a software tool, DBXten, which permits rapid ingestion, compact storage and sophisticated querying. This patent-pending tool for handling such data can be added to existing databases. Click here to read BCS’s DBXten presentation (a nine-page PDF file) prepared for the 2008 Annual Meeting of the Gulf of Mexico Hydrates Research Consortium.

The aim of this station is to monitor and investigate the hydrocarbon system within the hydrate stability zone of the northern Gulf of Mexico, and to remotely observe changes in the physical and chemical parameters of gas hydrates. A key component of the monitoring station is a vertical array of hydrophones which will record data that will be analyzed and interpreted using matched field techniques. The ultimate aim of this analysis is to use acoustic energy emitted by passing ships to monitor the sub-bottom layers in the region of the station, with the goal of detecting the occurrence of large-scale changes in the hydrate structures within these layers.

The monitoring station will be installed in 800 m of water in a gently sloping region of Mississippi Canyon Block 118 where hydrate deposits are present. The image below shows some surface properties of the bottom in this region. It is intended that data from the hydrophone array to be situated in this area will be collected and analyzed to detect sub-bottom changes in the hydrates structure.

Bathymetry and acoustic reflectivity of the ocean bottom of Mississippi Canyon Block 118 in the region of the monitoring station. The areas of high reflectivity (yellow and red) correspond to the likely presence of gas hydrates under a surface layer of carbonates.

BCS has designed and developed a simulation, data management and processing software system for the data from the hydrophone array. The purpose of the software is to provide a comprehensive and validated environment for investigating the application of matched field inversion (MFI) techniques to detect changes in the sub-bottom gas hydrate deposits. This approach is based on the expectation that MFI analysis of acoustic array data originating from nearby sources of opportunity (passing ships) can be used to detect such changes. The basic principle is to derive geoacoustic models for the current sub-bottom regions of the station by applying MFI to data from calibration measurements, and then use these models to match with future data obtained from passing sources. The presence of a large mismatch would be taken as evidence of a change.

The software developed by BCS provides a suite of components for generating synthetic data simulating shots and ship noise, transforming these data into a form where they can be used for matched field techniques, and applying these techniques to analyze the data. Methods for simulating acoustic array data from shots or ship noise were developed first, and then used to support the development and validation of matched field methods under controlled conditions. The result was that these methods are now in place and ready to be applied when real data from the array become available.