AAPG ANNUAL CONFERENCE AND EXHIBITION
Making the Next Giant Leap in Geosciences
April 10-13, 2011, Houston, Texas, USA
Primary Controls on Organic Carbon Content in UK Upper Mississippian Gas Shales
(1) University of Leicester, Leicester, United Kingdom.
(2) British Geological Survey, Keyworth, Nottingham, United Kingdom.
(3) NERC Isotopes Geoscience Laboratory, British Geological Survey, Keyworth, Nottingham, United Kingdom.
(4) Dipartimento de Scienze della Terra 'A. Desio', Università degli Studi di Milano, Milan, Italy.
(5) Department of Earth Sciences, Memorial University of Newfoundland, St. Johns, NF, Canada.
(6) British Geological Survey, Edinburgh, United Kingdom.
(7) Statoil Research Centre, Bergen, Norway.
In recent years, substantial progress has been made in the production technology and assessment of shale gas plays, however, the primary ecological and depositional controls of the enrichment and type of organic material into gas shales are less well studied. These parameters have a major impact on the amount and quality of the associated gas.
Thick Namurian organic-rich mudstones in northern England are within the gas window. Complex palaeoecological and sedimentological processes, combined with cyclical sea level changes, influenced the type and distribution of organic matter input into the mudstones. The apparently monotonous mudrocks typically hold between 1 and 7% total organic carbon (TOC). Terrestrial plants as well as phytoplanktonic and other algae contributed to the organic carbon content of the deposits. The terrestrial material was delivered into the basin from river mouths and occurs throughout the entire mudstone succession, whereas the phytoplanktonic and other algae appear to be only associated with marine sediments.
This study investigates the biological influences on the quality of mudstones as a source and reservoir of shale gas. In detail, the objectives are to: (1) interpret different lithofacies in terms of sedimentary processes and changing local environment; (2) investigate the distribution and abundance of organic matter in relation to lithofacies and determine their potential for gas generation; (3) link palaeoenvironments to larger scale climate change and carbon cycle events; and finally (4) develop a predictive model relating biological input to shale gas prospectivity. For this, a multidisciplinary approach is used. Optical imaging of thin sections allows detailed lithofacies analyses. δ13Corg data are used to delineate horizons with organic material from terrestrial versus marine sources, including the recognition of cryptic marine bands. These techniques are combined with the analysis of palynological samples to document basin-wide changes in environmental conditions.