OR/14/056 About the Total Organic Carbon (TOC) dataset

From Earthwise
Jump to: navigation, search
Cooke, I L. 2014. User Guide Total Organic Carbon (TOC) data. British Geological Survey Internal Report, OR/14/056.

Background

Great Britain has abundant shale at depth although the distribution is not well known. The BGS is investigating the location, depth and properties of the shale as well as the processes that lead to economic accumulations of gas.

BGS has produced a review dataset, based on existing published analyse. The data has been compiled as part of ongoing research of shale gas basins through the use of conventional oil and gas well data to identify potential targets; for example, total organic carbon and shale formation crops and thicknesses. This dataset represents the data gathered for this purpose and provides information on the content and variation within prospective some shale units.

Rock property characteristics, which are a function of the original depositional setting, subsequent geological history and mineralogy, are used to infer the possible presence of shale gas. A number of factors are considered in determining the quality of a source rock including:

  • Total Organic Carbon (TOC)
  • Net to gross organic-rich shale thicknesses
  • Kerogen type
  • Thermal maturity
  • Porosity and transport properties
  • Fracture properties

These result in the thermal decomposition of organic matter at depth and under high pressures. This process is often associated with coal, oil and gas fields and may be locally important where gasses have migrated from depth; or where there is slow release from previously deeply buried, low permeability, organic-rich rocks. It can be measured by heating a rock sample at very high temperatures in a furnace and combusting the carbon (organic matter) into carbon dioxide (CO2). The amount of CO2 that is released is proportional to the carbon content of the rock sample. The sample may also contain non-organic sources of carbon such as calcite or siderite and their presence must be corrected (using acid digestion) in order to determine an accurate TOC content.

The data has been derived from borehole analysis, with sampling being undertaken by the BGS Organic Geochemistry Laboratory. The analysis results are supported by expert knowledge, the dataset also underpins the conclusions published in Smith (2010)[1].

The data reflects already processed and validated boreholes. BGS holds more data of this type and work is continuing to validate further borehole data.

The British Geological Survey has an ongoing development programme to produce datasets that inform and support research. A suite of energy related datasets are currently under development and these are complimented by existing BGS assets.

The data has been derived from publications of analyses of organic rich shale sampled from BGS (formerly IGS) boreholes (see Smith 2010).Related products:

Products under development:

  • Vitrinite reflectance

Who might require this data?

  • Hydrocarbons exploration companies
  • Hydrocarbons service companies
  • Central government
  • Academic researchers and modellers

Total organic content, the amount of organic carbon in a geological formation is an indicator in exploration for shale gas/oil. Anyone involved in hydrocarbon exploration, government decision makers or academics working in the field of shale gas exploration and development may be interested in this dataset.

Extensive research is currently being carried out in this area and whilst the dataset currently encompasses a limited number of borehole locations it is expected that further boreholes will be interpreted and will continue to be added.

What the dataset shows?

The dataset shows location of boreholes where TOC analysis has been carried out. Each borehole has been sampled at a series of depths and samples have been analysed to evaluate the total organic content of each sample. The results of the analysis are given in the attribute table, the analysis techniques and table fields are described in the Technical Information section below.

References

  1. SMITH, N, TURNER, P, WILLIAMS, G. 2010 UK data and analysis for shale gas prospectivity. In: Vining, B A, Pickering, S C, (eds.) Petroleum Geology: From Mature Basins to New Frontiers: Proceedings of the 7th Petroleum Geology Conference. Geological Society of London, 1087–1098.