No description available.

No description available.

Quartz cement is a major culprit of porosity and permeability loss in deeply buried sandstone hydrocarbon reservoirs. A major debate is whether quartz cement is entirely internally derived or if fluid flow and mass transfer can import silica for quartz cementation. Two Late Jurassic normal faults are exposed within the aeolian (U. Permian) Hopeman Sandstone, onshore within the Inner Moray Firth basin, UK North Sea. The Clashach Fault has a throw <50m. The Burghead Fault has a throw of>100m. The faults crop out within the Hopeman Horst on the southern margin of the 50km wide, 5km deep, half-graben basin. Maximum burial depth of the Hopeman Sandstone within this horst block is 1.5-2.4km. Quartz cementation is asymmetric across the fault planes. Moving through the footwall of the Clashach Fault toward the fault plane, quartz cement volume increases from 9% at 31.7m to a maximum of 26.5% at 13.8m from the plane. From 13.8m to 0.5m from the fault plane authigenic quartz volume decreases from 26.5% to 4.2% at 0.5m. In this zone carbonate cement, which later dissolved, reduced the space available for quartz precipitation. The hanging wall contains mean 4% authigenic quartz. Porosity displays an inverse relationship to quartz cement. Footwall porosity increases from 10% at 13.8m from the fault plane to 18.6% at 31.7m. From 13.8m-0.5m porosity varies inversely with the volume of quartz cement in each sample. Hanging wall mean porosity is 24.5%. Footwall intergranular volume decreases from a maximum of 32% at 13.8m to 28% at 31.7m. At the Burghead Fault, footwall authigenic quartz volume increases moderately from 24.5% at 13m from the fault plane to 29% at 0.5m from the fault plane. Porosity displays an increase from 2.3% at 0.5m to 6.1% at 13m. Permeability decreases from 100-1000mD in poorly cemented hanging wall sandstone to <1mD in extensively quartz cemented sandstones in the footwalls of both faults. Footwall intergranular volume is consistently >30% in the Burghead Fault footwall. Fluid inclusions within footwall quartz overgrowths are single phase, aqueous, indicating cement precipitation <60°C. Quartz cemented microfracture fluid inclusion trails, generated during fault movement, contain 2-phase (L+V) aqueous inclusions with mean homogenisation temperature of 166°C, recording the presence of hot fluids in the sandstone at the time of faulting. Ion microprobe analysis of quartz overgrowth oxygen isotope values for footwall cements around the Clashach Fault shows a linear increase of 8180 values with increasing distance from the fault plane from +17.9960 at 4.2m to +20.8%o at 30.8m. In quartz cements in the footwall of the Burghead Fault, 5180 rises from +17.53% at 0.1m from the fault plane to a consistent range of +19.1%o to +19.596o up to 14m distant. Hanging wall cements have a mean 6180 +23.8960 with range of 6180 +20.1ß'w to +25.09'. 0. An isotopic profile across a single quartz cemented deformation band shows 00 is a minimum mean of +20.7%o. Oxygen isotope and fluid inclusion data records quartz cementation from hot basinal fluids which entered the Hopeman Sandstone adjacent to fault planes. This fluid cooled and mixed with Jurassic meteoric porefluids, precipitating quartz cement at a burial depth of <1.25km. Siliceous fluids were sourced from sediment compaction following Late Jurassic extension in the basin and were expelled up-dip toward the basin margin. Fluid flow was locally focused through the Hopeman Horst, which acted as an exit point for regional fluid expulsion. Within the horst block advecting fluid flow was focused into basinward footwalls by the low permeability vertical fault planes. This was aided by an enhanced reduction in fault permeability by quartz cementation of deformation bands at shallow burial (500m

Naturally deformed clastic rocks such as breccias and conglomerates provide a useful way to study strain and, indh:ectly, the rheology of rocks. However plastic deformation processes may potentially compromise many of the commonly used methods of determining strain in such rocks at high temperatures, since many of these strain analysis techniques rely upon changes in object e.g. grain shape, orientation and distribution. The work reported in this. thesis explores this matter quantitatively by performing a number of deformation experiments on synthetic calcite 'conglomerates' at temperatures where the rate-dependence of grain size-sensitive deformation processes in the clast and matrix can beú varied. In order to control the microstructures of the experimental samples, specimens were fabricated by mixing granulated Solnhofen limestone with powders of Chelometric grade calcite. The mixtures were tumbled for 3 hours duration to ensure uniform intermixing of the powders, and were then hot-isostatically pressed at a temperature of 700úC under a confining pressure of 190 MPa for 72 hours. The resulting samples were fully dense and consisted of sub-angular Solnhofen limestone clasts 60-90J.Ull in diameter, in a foam-textured matrix of Chelometric grade calcite with a grain size of22.2J.Ull ñ7.5J.Ull. All experiments were conducted at temperatures ranging between 400ú -700úC, and at a constant confining pressure (158 MPa) and strain rate (3.0xlO-4 S-I). An initial set of deformation experiments were performed upon pure Solnhofen limestone and Chelometric grade calcite to establish the flow behaviour of the clasts and matrix, respectively. Subsequent experiments were performed upon samples in which the volume fraction of clasts and matrix varied in the range 9:91 to 37:63. In order to assess the accuracy of strain measurements made on deformed conglomerates and, in particular, the potential complicating influence of grain size-sensitive flow on those measurements, the Rf/J and Fry techniques have been used to determine the clast and matrix strains, respectively, in the experimental samples. Detailed microstructural analyses were performed using an automated Electron Backscatter Diffraction (EBSD) technique. The experimental results obtained emphasize the significant role that viscosity contrasts, volume fraction and microstructure have in controlling the bulk strengths of polyphase materials. The results also show that at 550úC there is no strain partitioning between the clast and matrix despite the large viscosity contrast between them whereas at 700úC there is a small but consistent strain partitioning. A rigorous interrogation of the results using the law of mixtures has shown that the component of strain which is accommodated by grain boundary sliding can be quantified in these experiments. Microstructural analysis has shown clearly a temperature dependent change in the development of fabric intensity with strain which may provide a new insight into inferring true bulk strains in rocks deformed at high temperatures.

No description available.

No description available.

No description available.

No description available.

In this work, high-resolution (pressure decay profile permeametry, PDPK and image analysis porosimetry) techniques supported by more conventional core analysis measurements and integrated with macroproperty measurements have been used in the detailed fault seal analysis of deformation bands from two different geological settings. The Hopeman Sandstone, (Inner Moray Firth Basin) is host to cataclastic deformation bands and the sandstone samples from the U.K. sector of southern North Sea host clay-rich bands. With the exception of cemented deformation bands, their formation is shown to be highly dependent upon the composition of the host rock. Detailed PDPK permeability and image analysis porosity maps document microscale changes in permeability and porosity across deformation bands which have experienced varying levels of cataclasis, clay mixing and cementation processes. The greater difference in permeabilities and porosities of deformation bands relative to host rock using these techniques compared to conventional nitrogen permeametry and helium, mercury and Nuclear Magnetic Resonance (NMR) porosimetry is the outcome of their higher spatial resolution resulting in measurements of much smaller volumes or rock. Together with pore-size distribution, capillary pressure, (Scanning electron microscopy, SEM and mercury) grain size and macroproperty characterisation, these results show much reduced deformation band storage capacities relative to the host rock and illustrates their influence as baffles to flow. This effect has been observed directly using positron emission tomography (PET) scanning of deformation bands. Cemented deformation bands (observed using cathodoluminescence, CL) locally tighten the Hopeman Sandstone but are discontinuous and unlikely to have a large impact on fluid flow throughout the fault damage zone.

No description available.