Vertical effective stress as a control on quartz cementation in sandstones

Temperature-controlled precipitation kinetics has become the overwhelmingly dominant hypothesis for the control of quartz cementation in sandstones. Here, we integrate quantitative petrographic data, high spatial resolution oxygen isotope analyses of quartz cement, basin modelling and a kinetic model for quartz precipitation to suggest that the supply of silica from stress-sensitive intergranular pressure dissolution at grain contacts is in fact a key control on quartz cementation in sandstones. We present data from highly overpressured sandstones in which, despite the current burial temperature of 190 °C, quartz cement occurs in low amounts (4.6 ± 1.2% of bulk volume). In situ oxygen isotope data across quartz overgrowths suggest that cementation occurred over 100 Ma and a temperature range of 80–150 °C, during which time high fluid overpressures resulted in consistently low vertical effective stress. We argue that the very low amounts of quartz cement can only be explained by the low vertical effective stress which occurred throughout the burial history and which restricted silica supply as a result of a low rate of intergranular pressure dissolution at grain contacts

Geological repositories: scientific priorities and potential high-technology transfer from the space and physics sectors

The use of underground geological repositories, such as in radioactive waste disposal (RWD) and in carbon capture (widely known as Carbon Capture and Storage; CCS), constitutes a key environmental priority for the 21st century. Based on the identification of key scientific questions relating to the geophysics, geochemistry and geobiology of geodisposal of wastes, this paper describes the possibility of technology transfer from high-technology areas of the space exploration sector, including astrobiology, planetary sciences, astronomy, and also particle and nuclear physics, into geodisposal. Synergies exist between high technology used in the space sector and in the characterization of underground environments such as repositories, because of common objectives with respect to instrument miniaturization, low power requirements, durability under extreme conditions (in temperature and mechanical loads) and operation in remote or otherwise difficult to access environments

The Geothermal Potential Held within Carboniferous Sediments of the East Midlands: A New Estimation Based on Oilfield Data

ABSTRACT Carboniferous sediments have, to date, been largely ignored when UK geothermal resource assessments have been made. Resources located within deep sedimentary Mesozoic basins, and those associated with radiothermal granites have formed the main focus of resource quantification in recent years. There has been no attempt to formally quantify the resource located within Carboniferous sediments due to their complex structural and diagenetic history. The East Midlands Petroleum Province is the onshore extension of the Southern North Sea Basin. Oil reserves are typically found in Upper Carboniferous sandstone units, and rarely in Lower Carboniferous (Dinantian) Limestones. Exploration within the East Midlands has led to the discovery of over 30 separate fields. In 2011, IGas Energy PLC (IGas) purchased and now operates 16 of these fields. The well records and production data that were obtained as a result of this procurement has been used to produce a first quantification of the geothermal resource held within Carboniferous strata. Using known production data, Horner-corrected formation temperatures and oil/water specific gravity from 23 fields, a value of stored heat has been obtained for each field. In total, the geothermal resource has been approximated as being between 1.74 MW t and 4.36 MW t . Given these fields cover only 0.78% of the East Midlands total area, the potential for a larger geothermal resource base is likely to exist. Removal and sale of heat from the co-produced water will improve the economics of tail end production by lowering the effective total operating expenditure. Reinjection of the cooled water could also help increase the recovery factor of the reservoir; the cooled water having a higher viscosity and hence lower mobility ratio contrast with the oil than would hot water

Rapid Moment Magnitude (Mwp) Calculation for UK Broadband Seismic Stations Using Teleseismic Waves

Determining the magnitude of an earthquake rapidly and correctly is essential to starting simulations to evaluate the potential for tsunami generation and early warning for tsunami-prone countries and rapid response, considering countries that lie in seismically active regions. Although the UK does not have a high degree of tsunami hazard, the UK seismic network can estimate the moment magnitude for large earthquakes which will occur around the globe. This study aimed to test the UK Seismological Network Broadband Seismic Stations to calculate the P-wave moment magnitude (Mwp) using teleseismic waves. The standard way to calculate the Mwp is using the P-wave portion of a seismic wave recorded at different epicentral distances. We selected twenty-five seismic events with a magnitude greater than 6.5Mw and epicentral distances between 17 and 90 degrees. The main issue is selecting the P-wave portion of a seismic wave and using a trial P-wave velocity to estimate the Mwp. We simplified the selection of a P-wave portion of seismic waves using a theoretical formula that works with epicentral distance, P-wave arrival time and an apparent P-wave velocity, which calculates the S-wave arrival time. The results show the variation between the Harvard centroid moment tensor (CMT—Mw) and Mwp, which is about ± 0.1 magnitude units in most events and ± 0.2 for some events. These results prove the Mwp technique can be applied to the UK broadband seismic network broadband seismic stations and encourage the use of it immediately following a destructive earthquake anywhere in the world