Feature 'a hard rain's a-gonna fall': torrential rain, flash floods and desert lakes in the Late ... more Feature 'a hard rain's a-gonna fall': torrential rain, flash floods and desert lakes in the Late triassic arden Sandstone of Central england the arden Sandstone Formation of central and western england is a thin but conspicuous arenaceous unit within the Late triassic Mercia Mudstone Group. Sedimentological and palaeontological data point to lacustrine depositional conditions, in contrast to the red desert mudstones above and below which were deposited as continental dryland desert floodplains. the arden Sandstone records deposits of the lake margins and may be the high stand lateral equivalent of the halite and gypsum deposits which formed in the lake centre. the Carnian age of the arden Sandstone potentially links it to the Carnian Pluvial episode, marking the coalescence, spread and freshening of the formerly saline desert lakes, and deposition of sandy, fluvial and lacustrine deposits, during the wetter climate that prevailed for at least a million years.
Bulletin of the Geological Society of Malaysia, 2023
The pre-Cretaceous history of Borneo remains relatively poorly studied. Limited exposures of Pala... more The pre-Cretaceous history of Borneo remains relatively poorly studied. Limited exposures of Palaeozoic and lower Mesozoic rocks are located in NW Kalimantan and in West Sarawak, an area interpreted as the West Borneo basement. Lower Mesozoic sedimentary rocks in West Sarawak were analysed to study their depositional environments and implications for the tectonic evolution. Upper Triassic turbidites in West Sarawak, exposed in the northern part of Kuching city, informally named the Kuching Formation, are the deep marine equivalent to the more widespread, shallow marine Sadong Formation. The Kuching Formation comprises thinly-bedded stacked turbidites, consisting of incomplete Bouma sequences, with multiple, erosive channel sandstone bodies deposited under upper flow regime waning flows. Thin debrites with abundant coaly-material are interbedded with the channel sandstones. The Kuching and Sadong formations both contain volcaniclastic detritus that was derived from the westward-subducting Palaeo-Pacific plate, forming a Triassic Andean-type arc which extended from West Borneo in the south to southern China, Taiwan and Japan in the north. Palaeoproterozoic to Archean detrital zircons in the Kuching and Sadong formations reveal a Cathaysian basement source, providing insights into the nature of the West Borneo basement. Quartz-mica schists (Kerait Schist, Tuang Formation) in fault-contact with the two sedimentary successions may have formed during accretion.
There is renewed interest in a series of Carnian-aged sandstone units across the UK because they ... more There is renewed interest in a series of Carnian-aged sandstone units across the UK because they represent a unique event in the Late Triassic, the Carnian Pluvial Episode (CPE), from 233 to 232 Ma. The North Curry Sandstone Member of the Mercia Mudstone Group in Somerset is of particular importance because it yielded a rich fauna of shark, bony fish and amphibian remains in coarse-grained sandstones to Charles Moore in the 1860s. However, the exact location and age of his important collection had not been identified. Here, we demonstrate that the Moore collection comes from the North Curry Sandstone Member in a location in the village of Ruishton, just east of Taunton, where a new road cutting reveals both the bone-rich units and a complete succession through the CPE, a time of major climatic and biotic upheaval. The 16 m section comprises several sandstones interbedded with red-green mudstones, representing a terrestrial environment with lacustrine, evaporitic mud flat and fluvial deposits.
Lower Cretaceous (Aptian-Albian) sandstones of the Ghaggar-Hakra Formation in the Barmer Basin of... more Lower Cretaceous (Aptian-Albian) sandstones of the Ghaggar-Hakra Formation in the Barmer Basin of northwest Rajasthan, India, have a complex depositional history which is confusing given they are quartzose arenites. The heavy mineral grains are very well-rounded, and the assemblage is dominated by zircon and rutile grains suggesting that the sediments have been recycled multiple times, whilst the presence of staurolite indicates a metapelite provenance component.
Petrographical analysis suggests that extreme diagenesis cannot account for the quartzose arenite composition, despite Early Cretaceous soil formation and at least two periods of subsequent telogenetic modification. An alternative explanation to extreme chemical weathering in the provenance area is that the Ghaggar-Hakra sandstones are multi-cycle sediments derived, at least in part, from the quartzose arenites of the Cambrian Jodhpur Group. This analysis suggests that variations in detrital mineralogy across the Western India Rift System and Indus Basins are the result of transcontinental fluvial transport systems sourcing sediment from specific basement highs (Nagar Parker High, Devikot High, Deodar Ridge and Aravalli Mountain Range) mixed with varying proportions of sediment derived from sandstones of the Jodhpur Group. Consequently, we suggest that Cretaceous fluvial systems were controlled by the local palaeogeographies within the failed rifts of the Barmer and Cambay Basins and that both basins formed barriers to sediment transport from the Aravalli Mountain Range across the northwest Indian plate and into surrounding basins.
The Raageshwari Volcanic Formation (RVF) is a volcanic complex in the southern part of the Barmer... more The Raageshwari Volcanic Formation (RVF) is a volcanic complex in the southern part of the Barmer Basin, NW India, localized around a large rift centre horst block, the Central Basin High. The RVF comprises an initial sequence of acid igneous rocks, which are of ignimbritic origin, termed the Agni Member, overlain by a stacked sequence of basaltic lava flows interbedded with subordinate pyroclastic deposits, the Prithvi Member. Seismic data confirms that the volcanic complex has a conical overall geometry and a layered internal structure produced by successive and extensive flows of basalt and ignimbrite, very similar to that observed in the main Deccan lava outcrops along the western margin of India. U–Pb zircon ages near the top of the Agni Member in the Raageshwari-26 well give an age of 68+/ 2 Ma for a tephrite pyroclastic unit, whilst Ar–Ar analysis of a distal basalt containing phenocrysts of biotite from the Saraswati-4 well gave an older robust Ar–Ar plateau age of 73.7 ± 1.4 Ma. A typical Deccan age of 67.9 ± 1.7 Ma was obtained from the isolated unaltered basaltic andesite in well NE-South-1. Due to depositional on-lap onto the Central Basin High, the overlying alluvial Dandlawas and Fatehgarh formations are absent on the crest of the Central Basin High and Barmer Hill Formation lake sediments rest directly on the basalts. This relationship indicates that the volcanic cone was a structural or topographic high during deposition onto which the Fatehgarh and Barmer Hill formations lake sediments eventually on-lapped. The RVF of the Barmer Basin along with the Deccan volcanics in the Cambay Basin, Narmada Rift and in Saurasthra are all developed within fault-bounded rift basins, in which deep seated faults extend beneath the Deccan volcanic sequence. They are associated with thermal anomalies and thinned continental crust and the presence of a linear low velocity zone at ~100 km depth in the upper mantle region beneath the Barmer and Cambay basins. This is interpreted to be the position of the “conduit” through which plume head material passed through the upper mantle before arriving at the base of the Indian lithosphere. The RVF therefore appears to be an early eruption of differentiated ultrabasic magma from a shallow, secondary magma chamber produced by partial crustal melting.
The Northern Potwar Deformed Zone (NPDZ) of the frontal Himalayas in northern Pakistan hosts many... more The Northern Potwar Deformed Zone (NPDZ) of the frontal Himalayas in northern Pakistan hosts many oil and gas fields located in thrust sheets and associated folds. The presence of fractures in Paleogene carbonates at >3 km target depths with very little or no primary porosity is an essential part of reservoir storage and connectivity. Predicting fracture presence, distribution and orientation is therefore key to successful exploration, appraisal and field development in the NPDZ. The Ratana field is an underdeveloped fractured carbonate reservoir in the NPDZ. Advanced offset vector tile (OVT) PSTM and PSDM processing of a new generation of wide azimuth 3D seismic acquired across the field followed by seismic attribute generation and fracture modelling was used to investigate structural complexities and image fracture networks. Fracture strike characteristics are revealed by PSDM seismic attributes, OVT fracture prediction, FMS/FMI data and structural interpretation across a range of scales. The resulting seismic images show the presence of major WNW-ESE trending back thrusts which cross the field, and predict that steeply-dipping fracture systems are spatially associated with these thrusts. The strike of the OVT-predicted fractures is consistent with the regional trend of the Ratana field bounding thrusts, as well as with the orientation of fractures indicated from FMI/FMS logs. Fractured reservoir is best developed in the Paleocene Patala and Lockhart Formation limestones but is poor in the Eocene Sakesar Formation. Fractured limestone reservoirs occur in the western part of the field where thrust intensity is high, but are less well developed in the gently folded anticline in the eastern part of the field. OVT fracture prediction surface maps are consistent with production data from the field in that areas of high fracture intensity in wells Ratana-2 and Ratana-4 are associated with higher production compared to the less well fractured areas around the Ratana-1and Ratana-3 wells. The advanced seismic acquisition and processing is thus an exceptional example of a step change in seismic imaging at the reservoir and deeper levels, enabling compartment and fracture prediction to provide the Ratana field with a new lease of life. This fracture prediction approach provides a new structural framework for further exploration across the NPDZ and also potentially in other onshore fold-and-thrust belts.
Seismic structural interpretation reveals that the Zamzama Field structure is a single, asymmetri... more Seismic structural interpretation reveals that the Zamzama Field structure is a single, asymmetric, thrusted anticline with two discrete culminations in the hangingwall and a well resolved, pronounced thrust and an original common GWC across these two culminations. Re-interpretation using an Offset Vector Tiling (OVT) re-processed seismic volume indicates that the main thrusts defining the Zamzama structure are much less continuous than previously considered and generally do not hard link. Even the main crestal thrust is discontinuous and separated by a major lateral ramp in the Zamzama East-1 well area, linking the hanging wall with the footwall. These lateral ramps, effectively relay ramps, extend between all crestal thrusts and provide access to the common aquifer across the hanging wall part of the field. There are therefore no separate structural compartments in the hanging wall that are pressure isolated. This absence of compartmentalisation is a major result of the new structural interpretation as the old model was unable to explain the differential water ingress onto the crest of the structure.
Fractures in limestones of the Palaeocene Lockhart Formation in the hanging wall of the Himalayan... more Fractures in limestones of the Palaeocene Lockhart Formation in the hanging wall of the Himalayan Main Boundary Thrust north of Islamabad are examined, and the data analysed using a combination of topology and fractal dimension to characterise fracture patterns and relate them to structural domains. Neither technique alone allows the recognition of the structural domains. However, when considered together for all the fractures within an area, fore-thrusts, pop-ups and back-thrusts can be distinguished. The fractures are considered together, as the characteristics of the individual structural domains are characterised by the cumulative effect of all the different fractures, and in these complexly fractured rocks, the concept of fracture sets is problematic. Fore-and back-thrusts have higher fractal dimensions than pop-up structures. The highest fractal dimensions of both types of thrusts occur immediately adjacent to and decrease away from the central pop-up structure. Topologically, fore-thrust domains have fewer fractures and fracture intersections (nodes), with a longer mean fracture trace length; back-thrust domains contain more nodes (hence also more tips, lines, and branches) resulting in higher fracture densities. Pop-up structure domains are characterised by a low fracture intensity. Using the combined analysis of both the topology and fractal dimension, we show that the fracture pattern characteristics are predictable when related to the different structural settings identified within fold and thrust of the Lockhart Formation.
The Moab Anticline, east-central Utah, is an exhumed hydrocarbon palaeo-reservoir which was suppl... more The Moab Anticline, east-central Utah, is an exhumed hydrocarbon palaeo-reservoir which was supplied by hydrocarbons that migrated from the Moab Fault up-dip towards the crest of the structure beneath the regional seal of the Tidwell Mudstone. Iron oxide reduction in porous, high permeability aeolian sandstones records the secondary migration of hydrocarbons, filling of traps against small sealing faults and spill pathways through the Middle Jurassic Entrada Sandstone. Hydrocarbons entered the Entrada Sandstone carrier system from bends and other leak points on the Moab Fault producing discrete zones of reduction that extend for up to 400 m from these leak points. They then migrated in focussed stringers 2-5 m in height to produce accumulations on the crest of the anticline. Normal faults on the anticline were transient permeability barriers to hydrocarbon migration producing a series of small compartmentalized accumulations. Exsolution of CO2 as local fault seals were breached resulted in calcite cementation on the up-dip side of faults.
Field observations on the distribution of iron oxide reduction and calcite cements within the anticline indicate that the advancing reduction fronts were affected neither by individual slip bands in damage zones around faults nor by small faults with sand:sand juxtapositions. Faults with larger throws produced either sand/mudstone juxtapositions or sand:sand contacts and fault zones with shale-smears. Shale-smeared fault zones provided seals to the reducing fluid which filled the structural traps to spill points.
The Cairn India operated Ravva Field is located off the shore of the Godavari Delta, within the K... more The Cairn India operated Ravva Field is located off the shore of the Godavari Delta, within the KG Basin, on the east coast of India. Oil and gas reserves were discovered in 1987 by the well R-2, which penetrated the then proposed middle Miocene sandstones. These Miocene sandstones were deposited in a NE-SW oriented, wave dominated and lower to upper shoreface, cut by fluvial distributary channels. During the Pliocene to recent times the basin underwent several episodes of tectonic movement which has reactivated pre-existing faults. As a result tilted and rollover fault blocks provide the trapping mechanism in the field. The exceptional quality Miocene reservoirs, comprising high porosity, multi-darcy sands, are sealed by overlying early Pliocene shales. Within the initial phase of field development an extensive suite of litho-biostratigraphic, core, wireline log, and borehole image data together with structural dip data were used to construct a depositional and palaeogeographic mod...
The Cairn India operated Ravva Field is located off the shore of the Godavari Delta, within the K... more The Cairn India operated Ravva Field is located off the shore of the Godavari Delta, within the KG Basin, on the east coast of India. Oil and gas reserves were discovered in 1987 by the well R-2, which penetrated the then proposed middle Miocene sandstones. These Miocene sandstones were deposited in a NE-SW oriented, wave dominated and lower to upper shoreface, cut by fluvial distributary channels. During the Pliocene to recent times the basin underwent several episodes of tectonic movement which has reactivated pre-existing faults. As a result tilted and rollover fault blocks provide the trapping mechanism in the field. The exceptional quality Miocene reservoirs, comprising high porosity, multi-darcy sands, are sealed by overlying early Pliocene shales. Within the initial phase of field development an extensive suite of litho-biostratigraphic, core, wireline log, and borehole image data together with structural dip data were used to construct a depositional and palaeogeographic mod...
ABSTRACT: The Triassic Sherwood Sandstone Group comprises a complex of continental red beds depos... more ABSTRACT: The Triassic Sherwood Sandstone Group comprises a complex of continental red beds deposited by a major fluvial system flowing dominantly down a northerly inclined palaeoslope. Sedimentation took place in several distinct, tectonieally active basins with varying maximum burial depths, ranging from shallow (<1 km) to deep (>3 km). Despite proximal to distal variations in stream type, a distinct suite of early diagenetic events can be recognized throughout all the depositional basins, which is related to the depositional environment. These events are best preserved inthose basins with shallow burial histories, and show many similarities to the processes recorded from modern red beds of the Sonoran Desert, Baja California, although amore advanced grade of diagenesis has been reached in the Sherwood Sandstone. On the margins of the Irish Sea Basin in Cumbria, where burial was shallow, these early diagenetic textures are well preserved. The detrital grains underwent change...
Abstract: The structure and content of the Moab Fault zone are described for 37 transects across ... more Abstract: The structure and content of the Moab Fault zone are described for 37 transects across the fault zone where throws range from less than 100m to c. 960m. The 45km long fault trace intersects a sedimentary sequence containing a high proportion of sandstones with good reservoir properties, interspersed with numerous mudstone layers. Typically, the fault zone is bounded by two external slip zones with the fault zone components separated by up to nine internal slip zones. Fault zone components are tabular lenses of variably deformed sandstones and sandstone cataclasites and breccia, with a wide size range, usually enclosed in a matrix of shaley fault gouge containing mm to m scale ntrained sandstone fragments. Neither fault zone structure nor content can be predicted by extrapolation over distances as little as 10m. Although variable in thickness, haley gouge is always present except where the mudstone is <c. 20 % of the faulted sequence. The distribution of shaley gouge con...
Abstract: Structural geometries, faults and their movement histories, together with the petrophys... more Abstract: Structural geometries, faults and their movement histories, together with the petrophysical properties of flow units, are some of the major controls on hydrocarbon migration pathways within sedimentary basins. Currently, structural restoration, fault-seal analysis and hydrocarbon migration are treated as separate approaches to investigating basin geohistory and petroleum systems. Each of these separate modelling approaches in their own fields is advanced and sophisticated but they are not compatible with each other. Lack of integration produces incorrect palaeogeometries in basin models and inaccur-ate migration pathways. A combined structural restoration and fault-seal analysis technique, integrated with fast hydrocarbon migration pathway modelling code based on invasion percolation (IP) methods, is described. These modelling methods are used to develop a 4D basin modelling workflow in which evolving basin geohistories and geometries form an integral part of the analysis ...
The Moab Fault is a 28 mi (45 km) long, salt-related, normal fault of about 3,100 ft (950 m) maxi... more The Moab Fault is a 28 mi (45 km) long, salt-related, normal fault of about 3,100 ft (950 m) maximum surface throw. The fault cuts a Pennsylvanian to Cretaceous sedimentary sequence, and extends north-westwards from the Moab-Spanish Valley salt anticline along the south-western flank of a salt withdrawal syncline. The surface trace comprises a simple southern segment joined at branch-points to a series of fault splays in the north. Maximum surface throw occurs in the south where the fault is associated with both a footwall high and a hangingwall anticline. The fault trace is bordered by a damage zone, which includes a swarm of minor structures, that is most extensively developed within regions of structural complexity, for example around branch-points, fault bends, overlap zones and fault-related folds. The fault was active from the Triassic until at least the mid-Cretaceous. Distinctive types of veining, calcite cementation and iron oxide reduction are best developed adjacent to th...
Geological Society, London, Petroleum Geology Conference series
Of all the fossil fuels, natural gas is environmentally the cleanest, having a lower carbon conte... more Of all the fossil fuels, natural gas is environmentally the cleanest, having a lower carbon content with respect to energy output than either coal or oil. Global demand for gas has risen steadily over the last decade and forecast demand growth now outstrips all other major energy sources. These two factors should dictate that gas will remain the energy source of choice until renewable alternative energy sources become readily and economically available.The UK is set to face a shortage of proven indigenous gas reserves. However, the known conventional global resources of natural gas are very significant, with reserves projected to last for 60 years at current production levels, and expected un-discovered resources predicted to exceed this figure. In addition, huge volumes of ‘unconventional’ gas resources are trapped in hydrates on the seafloor, in coal beds, in low-permeability sandstone reservoirs (so-called ‘tight gas sands’) or in shale deposits. Whilst the global resource base i...
A multidisciplinary study of the gas-bearing Westphalian red bed sequence of the Southern North S... more A multidisciplinary study of the gas-bearing Westphalian red bed sequence of the Southern North Sea is presented. Comparison with analogous fades in Carboniferous sequences in the UK onshore and the eastern Netherlands suggests that two distinct alluvial red bed units are present, one of Westphalian C and one of Westphalian D age. Development of red pigment in these units was largely the result of contemporaneous pedogenesis. Interpretation of the stratigraphy is complicated by the widespread occurrence of reddening caused by penetrative weathering, both during the Carboniferous and related to the formation of the sub-Permian unconformity.Gas reservoirs are present in sandstones in the Westphalian C red bed unit. This unit has higher net:gross ratios and better poroperm characteristics than the underlying Coal Measures. The better reservoir quality in the red bed unit is largely influenced by late diagenetic alteration related to hydrocarbon migration.A sedimentological and diagenetic model for the formation of the Westphalian C red bed unit implies that this unit is likely to have a distinctive reservoir architecture, which, together with better reservoir qualities, distinguishes it from the hydrocarbon play in the underlying Coal Measures.
Feature 'a hard rain's a-gonna fall': torrential rain, flash floods and desert lakes in the Late ... more Feature 'a hard rain's a-gonna fall': torrential rain, flash floods and desert lakes in the Late triassic arden Sandstone of Central england the arden Sandstone Formation of central and western england is a thin but conspicuous arenaceous unit within the Late triassic Mercia Mudstone Group. Sedimentological and palaeontological data point to lacustrine depositional conditions, in contrast to the red desert mudstones above and below which were deposited as continental dryland desert floodplains. the arden Sandstone records deposits of the lake margins and may be the high stand lateral equivalent of the halite and gypsum deposits which formed in the lake centre. the Carnian age of the arden Sandstone potentially links it to the Carnian Pluvial episode, marking the coalescence, spread and freshening of the formerly saline desert lakes, and deposition of sandy, fluvial and lacustrine deposits, during the wetter climate that prevailed for at least a million years.
Bulletin of the Geological Society of Malaysia, 2023
The pre-Cretaceous history of Borneo remains relatively poorly studied. Limited exposures of Pala... more The pre-Cretaceous history of Borneo remains relatively poorly studied. Limited exposures of Palaeozoic and lower Mesozoic rocks are located in NW Kalimantan and in West Sarawak, an area interpreted as the West Borneo basement. Lower Mesozoic sedimentary rocks in West Sarawak were analysed to study their depositional environments and implications for the tectonic evolution. Upper Triassic turbidites in West Sarawak, exposed in the northern part of Kuching city, informally named the Kuching Formation, are the deep marine equivalent to the more widespread, shallow marine Sadong Formation. The Kuching Formation comprises thinly-bedded stacked turbidites, consisting of incomplete Bouma sequences, with multiple, erosive channel sandstone bodies deposited under upper flow regime waning flows. Thin debrites with abundant coaly-material are interbedded with the channel sandstones. The Kuching and Sadong formations both contain volcaniclastic detritus that was derived from the westward-subducting Palaeo-Pacific plate, forming a Triassic Andean-type arc which extended from West Borneo in the south to southern China, Taiwan and Japan in the north. Palaeoproterozoic to Archean detrital zircons in the Kuching and Sadong formations reveal a Cathaysian basement source, providing insights into the nature of the West Borneo basement. Quartz-mica schists (Kerait Schist, Tuang Formation) in fault-contact with the two sedimentary successions may have formed during accretion.
There is renewed interest in a series of Carnian-aged sandstone units across the UK because they ... more There is renewed interest in a series of Carnian-aged sandstone units across the UK because they represent a unique event in the Late Triassic, the Carnian Pluvial Episode (CPE), from 233 to 232 Ma. The North Curry Sandstone Member of the Mercia Mudstone Group in Somerset is of particular importance because it yielded a rich fauna of shark, bony fish and amphibian remains in coarse-grained sandstones to Charles Moore in the 1860s. However, the exact location and age of his important collection had not been identified. Here, we demonstrate that the Moore collection comes from the North Curry Sandstone Member in a location in the village of Ruishton, just east of Taunton, where a new road cutting reveals both the bone-rich units and a complete succession through the CPE, a time of major climatic and biotic upheaval. The 16 m section comprises several sandstones interbedded with red-green mudstones, representing a terrestrial environment with lacustrine, evaporitic mud flat and fluvial deposits.
Lower Cretaceous (Aptian-Albian) sandstones of the Ghaggar-Hakra Formation in the Barmer Basin of... more Lower Cretaceous (Aptian-Albian) sandstones of the Ghaggar-Hakra Formation in the Barmer Basin of northwest Rajasthan, India, have a complex depositional history which is confusing given they are quartzose arenites. The heavy mineral grains are very well-rounded, and the assemblage is dominated by zircon and rutile grains suggesting that the sediments have been recycled multiple times, whilst the presence of staurolite indicates a metapelite provenance component.
Petrographical analysis suggests that extreme diagenesis cannot account for the quartzose arenite composition, despite Early Cretaceous soil formation and at least two periods of subsequent telogenetic modification. An alternative explanation to extreme chemical weathering in the provenance area is that the Ghaggar-Hakra sandstones are multi-cycle sediments derived, at least in part, from the quartzose arenites of the Cambrian Jodhpur Group. This analysis suggests that variations in detrital mineralogy across the Western India Rift System and Indus Basins are the result of transcontinental fluvial transport systems sourcing sediment from specific basement highs (Nagar Parker High, Devikot High, Deodar Ridge and Aravalli Mountain Range) mixed with varying proportions of sediment derived from sandstones of the Jodhpur Group. Consequently, we suggest that Cretaceous fluvial systems were controlled by the local palaeogeographies within the failed rifts of the Barmer and Cambay Basins and that both basins formed barriers to sediment transport from the Aravalli Mountain Range across the northwest Indian plate and into surrounding basins.
The Raageshwari Volcanic Formation (RVF) is a volcanic complex in the southern part of the Barmer... more The Raageshwari Volcanic Formation (RVF) is a volcanic complex in the southern part of the Barmer Basin, NW India, localized around a large rift centre horst block, the Central Basin High. The RVF comprises an initial sequence of acid igneous rocks, which are of ignimbritic origin, termed the Agni Member, overlain by a stacked sequence of basaltic lava flows interbedded with subordinate pyroclastic deposits, the Prithvi Member. Seismic data confirms that the volcanic complex has a conical overall geometry and a layered internal structure produced by successive and extensive flows of basalt and ignimbrite, very similar to that observed in the main Deccan lava outcrops along the western margin of India. U–Pb zircon ages near the top of the Agni Member in the Raageshwari-26 well give an age of 68+/ 2 Ma for a tephrite pyroclastic unit, whilst Ar–Ar analysis of a distal basalt containing phenocrysts of biotite from the Saraswati-4 well gave an older robust Ar–Ar plateau age of 73.7 ± 1.4 Ma. A typical Deccan age of 67.9 ± 1.7 Ma was obtained from the isolated unaltered basaltic andesite in well NE-South-1. Due to depositional on-lap onto the Central Basin High, the overlying alluvial Dandlawas and Fatehgarh formations are absent on the crest of the Central Basin High and Barmer Hill Formation lake sediments rest directly on the basalts. This relationship indicates that the volcanic cone was a structural or topographic high during deposition onto which the Fatehgarh and Barmer Hill formations lake sediments eventually on-lapped. The RVF of the Barmer Basin along with the Deccan volcanics in the Cambay Basin, Narmada Rift and in Saurasthra are all developed within fault-bounded rift basins, in which deep seated faults extend beneath the Deccan volcanic sequence. They are associated with thermal anomalies and thinned continental crust and the presence of a linear low velocity zone at ~100 km depth in the upper mantle region beneath the Barmer and Cambay basins. This is interpreted to be the position of the “conduit” through which plume head material passed through the upper mantle before arriving at the base of the Indian lithosphere. The RVF therefore appears to be an early eruption of differentiated ultrabasic magma from a shallow, secondary magma chamber produced by partial crustal melting.
The Northern Potwar Deformed Zone (NPDZ) of the frontal Himalayas in northern Pakistan hosts many... more The Northern Potwar Deformed Zone (NPDZ) of the frontal Himalayas in northern Pakistan hosts many oil and gas fields located in thrust sheets and associated folds. The presence of fractures in Paleogene carbonates at >3 km target depths with very little or no primary porosity is an essential part of reservoir storage and connectivity. Predicting fracture presence, distribution and orientation is therefore key to successful exploration, appraisal and field development in the NPDZ. The Ratana field is an underdeveloped fractured carbonate reservoir in the NPDZ. Advanced offset vector tile (OVT) PSTM and PSDM processing of a new generation of wide azimuth 3D seismic acquired across the field followed by seismic attribute generation and fracture modelling was used to investigate structural complexities and image fracture networks. Fracture strike characteristics are revealed by PSDM seismic attributes, OVT fracture prediction, FMS/FMI data and structural interpretation across a range of scales. The resulting seismic images show the presence of major WNW-ESE trending back thrusts which cross the field, and predict that steeply-dipping fracture systems are spatially associated with these thrusts. The strike of the OVT-predicted fractures is consistent with the regional trend of the Ratana field bounding thrusts, as well as with the orientation of fractures indicated from FMI/FMS logs. Fractured reservoir is best developed in the Paleocene Patala and Lockhart Formation limestones but is poor in the Eocene Sakesar Formation. Fractured limestone reservoirs occur in the western part of the field where thrust intensity is high, but are less well developed in the gently folded anticline in the eastern part of the field. OVT fracture prediction surface maps are consistent with production data from the field in that areas of high fracture intensity in wells Ratana-2 and Ratana-4 are associated with higher production compared to the less well fractured areas around the Ratana-1and Ratana-3 wells. The advanced seismic acquisition and processing is thus an exceptional example of a step change in seismic imaging at the reservoir and deeper levels, enabling compartment and fracture prediction to provide the Ratana field with a new lease of life. This fracture prediction approach provides a new structural framework for further exploration across the NPDZ and also potentially in other onshore fold-and-thrust belts.
Seismic structural interpretation reveals that the Zamzama Field structure is a single, asymmetri... more Seismic structural interpretation reveals that the Zamzama Field structure is a single, asymmetric, thrusted anticline with two discrete culminations in the hangingwall and a well resolved, pronounced thrust and an original common GWC across these two culminations. Re-interpretation using an Offset Vector Tiling (OVT) re-processed seismic volume indicates that the main thrusts defining the Zamzama structure are much less continuous than previously considered and generally do not hard link. Even the main crestal thrust is discontinuous and separated by a major lateral ramp in the Zamzama East-1 well area, linking the hanging wall with the footwall. These lateral ramps, effectively relay ramps, extend between all crestal thrusts and provide access to the common aquifer across the hanging wall part of the field. There are therefore no separate structural compartments in the hanging wall that are pressure isolated. This absence of compartmentalisation is a major result of the new structural interpretation as the old model was unable to explain the differential water ingress onto the crest of the structure.
Fractures in limestones of the Palaeocene Lockhart Formation in the hanging wall of the Himalayan... more Fractures in limestones of the Palaeocene Lockhart Formation in the hanging wall of the Himalayan Main Boundary Thrust north of Islamabad are examined, and the data analysed using a combination of topology and fractal dimension to characterise fracture patterns and relate them to structural domains. Neither technique alone allows the recognition of the structural domains. However, when considered together for all the fractures within an area, fore-thrusts, pop-ups and back-thrusts can be distinguished. The fractures are considered together, as the characteristics of the individual structural domains are characterised by the cumulative effect of all the different fractures, and in these complexly fractured rocks, the concept of fracture sets is problematic. Fore-and back-thrusts have higher fractal dimensions than pop-up structures. The highest fractal dimensions of both types of thrusts occur immediately adjacent to and decrease away from the central pop-up structure. Topologically, fore-thrust domains have fewer fractures and fracture intersections (nodes), with a longer mean fracture trace length; back-thrust domains contain more nodes (hence also more tips, lines, and branches) resulting in higher fracture densities. Pop-up structure domains are characterised by a low fracture intensity. Using the combined analysis of both the topology and fractal dimension, we show that the fracture pattern characteristics are predictable when related to the different structural settings identified within fold and thrust of the Lockhart Formation.
The Moab Anticline, east-central Utah, is an exhumed hydrocarbon palaeo-reservoir which was suppl... more The Moab Anticline, east-central Utah, is an exhumed hydrocarbon palaeo-reservoir which was supplied by hydrocarbons that migrated from the Moab Fault up-dip towards the crest of the structure beneath the regional seal of the Tidwell Mudstone. Iron oxide reduction in porous, high permeability aeolian sandstones records the secondary migration of hydrocarbons, filling of traps against small sealing faults and spill pathways through the Middle Jurassic Entrada Sandstone. Hydrocarbons entered the Entrada Sandstone carrier system from bends and other leak points on the Moab Fault producing discrete zones of reduction that extend for up to 400 m from these leak points. They then migrated in focussed stringers 2-5 m in height to produce accumulations on the crest of the anticline. Normal faults on the anticline were transient permeability barriers to hydrocarbon migration producing a series of small compartmentalized accumulations. Exsolution of CO2 as local fault seals were breached resulted in calcite cementation on the up-dip side of faults.
Field observations on the distribution of iron oxide reduction and calcite cements within the anticline indicate that the advancing reduction fronts were affected neither by individual slip bands in damage zones around faults nor by small faults with sand:sand juxtapositions. Faults with larger throws produced either sand/mudstone juxtapositions or sand:sand contacts and fault zones with shale-smears. Shale-smeared fault zones provided seals to the reducing fluid which filled the structural traps to spill points.
The Cairn India operated Ravva Field is located off the shore of the Godavari Delta, within the K... more The Cairn India operated Ravva Field is located off the shore of the Godavari Delta, within the KG Basin, on the east coast of India. Oil and gas reserves were discovered in 1987 by the well R-2, which penetrated the then proposed middle Miocene sandstones. These Miocene sandstones were deposited in a NE-SW oriented, wave dominated and lower to upper shoreface, cut by fluvial distributary channels. During the Pliocene to recent times the basin underwent several episodes of tectonic movement which has reactivated pre-existing faults. As a result tilted and rollover fault blocks provide the trapping mechanism in the field. The exceptional quality Miocene reservoirs, comprising high porosity, multi-darcy sands, are sealed by overlying early Pliocene shales. Within the initial phase of field development an extensive suite of litho-biostratigraphic, core, wireline log, and borehole image data together with structural dip data were used to construct a depositional and palaeogeographic mod...
The Cairn India operated Ravva Field is located off the shore of the Godavari Delta, within the K... more The Cairn India operated Ravva Field is located off the shore of the Godavari Delta, within the KG Basin, on the east coast of India. Oil and gas reserves were discovered in 1987 by the well R-2, which penetrated the then proposed middle Miocene sandstones. These Miocene sandstones were deposited in a NE-SW oriented, wave dominated and lower to upper shoreface, cut by fluvial distributary channels. During the Pliocene to recent times the basin underwent several episodes of tectonic movement which has reactivated pre-existing faults. As a result tilted and rollover fault blocks provide the trapping mechanism in the field. The exceptional quality Miocene reservoirs, comprising high porosity, multi-darcy sands, are sealed by overlying early Pliocene shales. Within the initial phase of field development an extensive suite of litho-biostratigraphic, core, wireline log, and borehole image data together with structural dip data were used to construct a depositional and palaeogeographic mod...
ABSTRACT: The Triassic Sherwood Sandstone Group comprises a complex of continental red beds depos... more ABSTRACT: The Triassic Sherwood Sandstone Group comprises a complex of continental red beds deposited by a major fluvial system flowing dominantly down a northerly inclined palaeoslope. Sedimentation took place in several distinct, tectonieally active basins with varying maximum burial depths, ranging from shallow (<1 km) to deep (>3 km). Despite proximal to distal variations in stream type, a distinct suite of early diagenetic events can be recognized throughout all the depositional basins, which is related to the depositional environment. These events are best preserved inthose basins with shallow burial histories, and show many similarities to the processes recorded from modern red beds of the Sonoran Desert, Baja California, although amore advanced grade of diagenesis has been reached in the Sherwood Sandstone. On the margins of the Irish Sea Basin in Cumbria, where burial was shallow, these early diagenetic textures are well preserved. The detrital grains underwent change...
Abstract: The structure and content of the Moab Fault zone are described for 37 transects across ... more Abstract: The structure and content of the Moab Fault zone are described for 37 transects across the fault zone where throws range from less than 100m to c. 960m. The 45km long fault trace intersects a sedimentary sequence containing a high proportion of sandstones with good reservoir properties, interspersed with numerous mudstone layers. Typically, the fault zone is bounded by two external slip zones with the fault zone components separated by up to nine internal slip zones. Fault zone components are tabular lenses of variably deformed sandstones and sandstone cataclasites and breccia, with a wide size range, usually enclosed in a matrix of shaley fault gouge containing mm to m scale ntrained sandstone fragments. Neither fault zone structure nor content can be predicted by extrapolation over distances as little as 10m. Although variable in thickness, haley gouge is always present except where the mudstone is <c. 20 % of the faulted sequence. The distribution of shaley gouge con...
Abstract: Structural geometries, faults and their movement histories, together with the petrophys... more Abstract: Structural geometries, faults and their movement histories, together with the petrophysical properties of flow units, are some of the major controls on hydrocarbon migration pathways within sedimentary basins. Currently, structural restoration, fault-seal analysis and hydrocarbon migration are treated as separate approaches to investigating basin geohistory and petroleum systems. Each of these separate modelling approaches in their own fields is advanced and sophisticated but they are not compatible with each other. Lack of integration produces incorrect palaeogeometries in basin models and inaccur-ate migration pathways. A combined structural restoration and fault-seal analysis technique, integrated with fast hydrocarbon migration pathway modelling code based on invasion percolation (IP) methods, is described. These modelling methods are used to develop a 4D basin modelling workflow in which evolving basin geohistories and geometries form an integral part of the analysis ...
The Moab Fault is a 28 mi (45 km) long, salt-related, normal fault of about 3,100 ft (950 m) maxi... more The Moab Fault is a 28 mi (45 km) long, salt-related, normal fault of about 3,100 ft (950 m) maximum surface throw. The fault cuts a Pennsylvanian to Cretaceous sedimentary sequence, and extends north-westwards from the Moab-Spanish Valley salt anticline along the south-western flank of a salt withdrawal syncline. The surface trace comprises a simple southern segment joined at branch-points to a series of fault splays in the north. Maximum surface throw occurs in the south where the fault is associated with both a footwall high and a hangingwall anticline. The fault trace is bordered by a damage zone, which includes a swarm of minor structures, that is most extensively developed within regions of structural complexity, for example around branch-points, fault bends, overlap zones and fault-related folds. The fault was active from the Triassic until at least the mid-Cretaceous. Distinctive types of veining, calcite cementation and iron oxide reduction are best developed adjacent to th...
Geological Society, London, Petroleum Geology Conference series
Of all the fossil fuels, natural gas is environmentally the cleanest, having a lower carbon conte... more Of all the fossil fuels, natural gas is environmentally the cleanest, having a lower carbon content with respect to energy output than either coal or oil. Global demand for gas has risen steadily over the last decade and forecast demand growth now outstrips all other major energy sources. These two factors should dictate that gas will remain the energy source of choice until renewable alternative energy sources become readily and economically available.The UK is set to face a shortage of proven indigenous gas reserves. However, the known conventional global resources of natural gas are very significant, with reserves projected to last for 60 years at current production levels, and expected un-discovered resources predicted to exceed this figure. In addition, huge volumes of ‘unconventional’ gas resources are trapped in hydrates on the seafloor, in coal beds, in low-permeability sandstone reservoirs (so-called ‘tight gas sands’) or in shale deposits. Whilst the global resource base i...
A multidisciplinary study of the gas-bearing Westphalian red bed sequence of the Southern North S... more A multidisciplinary study of the gas-bearing Westphalian red bed sequence of the Southern North Sea is presented. Comparison with analogous fades in Carboniferous sequences in the UK onshore and the eastern Netherlands suggests that two distinct alluvial red bed units are present, one of Westphalian C and one of Westphalian D age. Development of red pigment in these units was largely the result of contemporaneous pedogenesis. Interpretation of the stratigraphy is complicated by the widespread occurrence of reddening caused by penetrative weathering, both during the Carboniferous and related to the formation of the sub-Permian unconformity.Gas reservoirs are present in sandstones in the Westphalian C red bed unit. This unit has higher net:gross ratios and better poroperm characteristics than the underlying Coal Measures. The better reservoir quality in the red bed unit is largely influenced by late diagenetic alteration related to hydrocarbon migration.A sedimentological and diagenetic model for the formation of the Westphalian C red bed unit implies that this unit is likely to have a distinctive reservoir architecture, which, together with better reservoir qualities, distinguishes it from the hydrocarbon play in the underlying Coal Measures.
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Papers by Stuart Burley
Petrographical analysis suggests that extreme diagenesis cannot account for the quartzose arenite composition, despite Early Cretaceous soil formation and at least two periods of subsequent telogenetic modification. An alternative explanation to extreme chemical weathering in the provenance area is that the Ghaggar-Hakra sandstones are multi-cycle sediments derived, at least in part, from the quartzose arenites of the Cambrian Jodhpur Group. This analysis suggests that variations in detrital mineralogy across the Western India Rift System and Indus Basins are the result of transcontinental fluvial transport systems sourcing sediment from specific basement highs (Nagar Parker High, Devikot High, Deodar Ridge and Aravalli Mountain Range) mixed with varying proportions of sediment derived from sandstones of the Jodhpur Group. Consequently, we suggest that Cretaceous fluvial systems were controlled by the local palaeogeographies within the failed rifts of the Barmer and Cambay Basins and that both basins formed barriers to sediment transport from the Aravalli Mountain Range across the northwest Indian plate and into surrounding basins.
Field observations on the distribution of iron oxide reduction and calcite cements within the anticline indicate that the advancing reduction fronts were affected neither by individual slip bands in damage zones around faults nor by small faults with sand:sand juxtapositions. Faults with larger throws produced either sand/mudstone juxtapositions or sand:sand contacts and fault zones with shale-smears. Shale-smeared fault zones provided seals to the reducing fluid which filled the structural traps to spill points.
Petrographical analysis suggests that extreme diagenesis cannot account for the quartzose arenite composition, despite Early Cretaceous soil formation and at least two periods of subsequent telogenetic modification. An alternative explanation to extreme chemical weathering in the provenance area is that the Ghaggar-Hakra sandstones are multi-cycle sediments derived, at least in part, from the quartzose arenites of the Cambrian Jodhpur Group. This analysis suggests that variations in detrital mineralogy across the Western India Rift System and Indus Basins are the result of transcontinental fluvial transport systems sourcing sediment from specific basement highs (Nagar Parker High, Devikot High, Deodar Ridge and Aravalli Mountain Range) mixed with varying proportions of sediment derived from sandstones of the Jodhpur Group. Consequently, we suggest that Cretaceous fluvial systems were controlled by the local palaeogeographies within the failed rifts of the Barmer and Cambay Basins and that both basins formed barriers to sediment transport from the Aravalli Mountain Range across the northwest Indian plate and into surrounding basins.
Field observations on the distribution of iron oxide reduction and calcite cements within the anticline indicate that the advancing reduction fronts were affected neither by individual slip bands in damage zones around faults nor by small faults with sand:sand juxtapositions. Faults with larger throws produced either sand/mudstone juxtapositions or sand:sand contacts and fault zones with shale-smears. Shale-smeared fault zones provided seals to the reducing fluid which filled the structural traps to spill points.