Palaeozoic petroleum systems of the Irish Sea

This report synthesises the results of the 21CXRM Palaeozoic project in the Irish Sea to describe the Palaeozoic petroleum systems of that area. One hydrocarbon play system dominates the basin system: Namurian organic-rich marine shales (Bowland Shale Formation) generated oil and gas with a peak during maximum burial of the system in late Jurassic/early Cretaceous time. These hydrocarbons passed to reservoirs in the Triassic Ormskirk Sandstone (Sherwood Sandstone Group) by way of structures generated during the Variscan Orogeny and Cenozoic inversion, resulting in the Morecambe, Hamilton and other gas and oil fields The Palaeozoic study of the wider Irish Sea area has assessed the potential for more widespread petroleum systems situated outside the well-known play, particularly within the Carboniferous. Within the Main Graben system of the East Irish Sea Basin, Coal Measures strata were partially removed following Variscan inversion and early Permian uplift. They are not rich in coals, and not inferred to be a significant source rock. There is some potential in the Millstone Grit and Yoredale sequences, as some shales (particularly those associated with marine bands) are known to have high Total Organic Contents. The source rock potential of shales within the Carboniferous Limestone sequence is poorly constrained by data. A Devonian source rock is unproven and considered unlikely. Potential Namurian source rocks, such as the Yoredale Group, have been largely eroded in the Peel and North Channel basins, considerably reducing their prospectivity, although terrestrial sequences of equivalent age in the Solway Basin may offer better potential. The variable seismic data quality at Carboniferous levels and sparsity of deep well control have led to challenges in interpretation, particularly of the deeper picks. The interpretation of the surfaces contains a strong model-driven element, evidenced by the onshore relationships and areas where seismic picks can be made with the greatest confidence. Based upon the integration of regional seismic mapping with a limited well, source rock and reservoir property dataset, the most prospective parts of the region, outside the Ormskirk conventional gas play, are considered to be: The thick Westphalian sequences preserved in the Eubonia Tilt-Block in Quadrant 109, outside the main Permian-Mesozoic graben system and unaffected by Cenozoic inversion. The presence and quality of seals form a major risk as the Cumbrian Coast Group seal is thin or absent and Carboniferous intraformational seals are required but untested. Based on the limited dataset available in adjacent basins, reservoir quality is also a significant risk. A belt of Variscan inversion structures correlated with structures on the Formby Platform, and Ribbledale Foldbelt onshore, from which hydrocarbons have leaked into the overlying, Ormskirk-hosted Hamilton fields. The biggest risk here is whether reservoirs remain unbreached at the Pre-Permian level, and retain good poroperm characteristics at depths of about 2500 m. A more speculative play lies in the extensive carbonate platform in Quadrant 109 and surrounding the Isle of Man, in reefal facies with enhanced secondary porosity. Here, source rock presence and migration pathways, reservoir properties and seal quality are major risks

A study of the f0(1370), f0(1500), f0(2000) and f2(1950) observed in the centrally produced 4pi final states

The production and decay properties of the f0(1370), f0(1500), f0(2000) and f2(1950) have been studied in central pp interactions at 450 GeV/c. The dPT, phi and |t| distributions of these resonances are presented. For the J = 0 states, the f0(1370) and f0(2000) have similar dPT and phi dependences. These are different to the dPT and phi dependences of the f0(980), f0(1500) and f0(1710). For the J = 2 states the f2(1950) has different dependences to the f2(1270) and f2'(1520). This shows that the dPT and phi dependences are not just J phenomena.Comment: 14 pages, Latex, 4 Figure

A coupled channel analysis of the centrally produced K+K- and pi+pi- final states in pp interactions at 450 GeV/c

A coupled channel analysis of the centrally produced K+K- and pi+pi- final states has been performed in pp collisions at an incident beam momentum of 450 GeV/c. The pole positions and branching ratios to pipi and KK of the f0(980), f0(1370), f0(1500) and f0(1710) have been determined. A systematic study of the production properties of all the resonances observed in the pi+pi- and K+K- channels has been performed.Comment: 16 pages, Latex, 5 Figure

Experimental evidence for a vector-like behaviour of Pomeron exchange

Evidence is presented that the Pomeron act as a non-conserved vector current. A study has been made of the azimuthal angle phi, which is defined as the angle between the pT vectors of the two outgoing protons, in the reaction pp -> pp(X0) for those resonances (X0) which are compatible with being produced by double Pomeron exchange. These distributions have been compared with a model which describes the Pomeron as a non-conserved vector current and a qualitative agreement is found. In addition, when one of the particles exchanged is known to have spin 0, namely pi-Pomeron exchange, the phi distribution is flat.Comment: 13 pages, Latex, 4 Figure

Seismic interpretation and generation of depth surfaces for Late Palaeozoic strata in the Irish Sea Region

This report describes the methodology and results of a regional seismic interpretation of the basins of the Irish Sea. It does not review the basins of the Celtic Sea. The aim of the interpretation was to map the distribution of Palaeozoic basins and highs, interpreting the key Devonian-Carboniferous surfaces and main structural elements of the area. About 40,000 km of 2D seismic reflection data have been interpreted and tied to key released wells in the project area. The seismic and well data were augmented by donated reports from sponsor companies. A set of 8 depth structure maps of key horizons have been produced for the pre-Permian succession. These maps provide a key dataset to aid assessment of the petroleum systems of the Palaeozoic strata within the study area. The surfaces, supplied digitally at a grid spacing of 5000 m, give a regional view of the topography of the horizons, and comprise: ‘UVAR’ (Variscan Unconformity) beneath Permian and Triassic strata Base Warwickshire Group (late Westphalian - ?Stephanian) Top Namurian (Base Pennine Coal Measures Group) Top Intra-Namurian (Top Bowland Shale in south, Base Millstone Grit elsewhere) Top Visean (Lower Carboniferous) Intra-Visean (amalgamated with Top Middle Border Group in north) Base Carboniferous (amalgamated with Base Clyde Plateau lavas in the North Channel to South-West Arran Sub-Basin) ‘UCAL’ Acadian (Caledonian) Unconformity) It is important to note that the variable data quality and sparsity of deep wells leads to a seismic interpretation which is strongly driven by regional geological models, themselves heavily dependent on inference from the onshore area. This is particularly the case with the deeper Carboniferous horizons which are not penetrated by any well and which may be only weakly reflective. In such cases, picks from better quality data may be interpolated through areas with poor quality data, as a modelled surface, to ensure a continuous surface for gridding. The well dataset has been re-interpreted (Wakefield et al., 2016) before integration with the seismic interpretation. The following general observations are made: The present study has confirmed the Permian-Mesozoic structural framework for the region established by Jackson and Mulholland (1993) and Jackson et al. (1995, 1996, 1997). The basin recognised in Quadrant 109 by Jackson and co-workers (op. cit.) is reinterpreted as a major Carboniferous half-graben structure controlled by a syndepositional fault on its NW side. It continues beneath thin Permo-Triassic cover into the Eubonia Basin and Ogham Platform, preserving a thick Westphalian succession, including inferred Warwickshire Group strata. It is inferred to have continued eastward into the Lagman Basin prior to its tectonic dissection by a combination of Variscan inversion and Permo-Mesozoic graben development along the Keys Fault. A belt of Variscan fold/thrust inversion structures on the Godred Croven Platform is correlated with structures on the Formby Platform and Ribblesdale Foldbelt onshore. CR/16/041 Last modified: 2016/05/30 09:37 10 The area of Carboniferous (undivided) subcrop depicted on mapping by BGS (1994) to north and west of the Isle of Man has been reclassified into Visean and Namurian elements. The presence of significant thicknesses of Carboniferous strata in the southern part of the North Channel is regarded as doubtful, but farther north, in the Larne, Rathlin and South-West Arran Sub-basins, greater thicknesses may be present. A detailed description of tectono-stratigraphic development based on the seismic interpretation is given in Pharaoh et al. (2016b), integrated with the petroleum system analysis

A study of the etapipi channel produced in central pp interactions at 450 GeV/c

The reaction pp -> pf (eta pi pi) ps has been studied at 450 GeV/c. There is clear evidence for an a2(1320)pi decay mode of the eta2(1645) and eta2(1870). In addition, there is evidence for an a0(980)pi$ decay mode of both resonances and an f2(1270)eta decay mode of the eta2(1870). No evidence is found for a JPC = 2++ a2(1320)pi wave.Comment: 15 pages, Latex, 4 Figures Branching ratio a2pi /f2 eta correcte

A search for charmonium states produced in central pp interactions at 450 GeV/c

A search for centrally produced charmonium states has been presented. There is no significant evidence for any charmonium production. An upper limit of 2 nb is found for the cross section of chic production using the decay chic(1P)-> J/psi gamma.Comment: 10 pages, Latex, 4 Figure

A study of the centrally produced pi0pi0pi0 channel in pp interactions at 450 GeV/c

The reaction pp -> pf (pi0pi0pi0) ps has been studied at 450 GeV/c. The pi0pi0pi0 effective mass spectrum shows clear eta(547) and pi2(1670) signals. Branching ratios for the eta(547) and pi_2(1670) are given as well as upper limits for the decays of the omega(782), a1(1260) and a2(1320) into 3pi0.Comment: 10 pages, Latex, 4 Figure

A study of the centrally produced baryon-antibaryon systems in pp interactions at 450 GeV/c

A study of the centrally produced ppbar, ppbarpi, ppbarpipi and lambda lambda channels has been performed in pp collisions using an incident beam momentum of 450 GeV/c. No significant new structures are observed in the mass spectra, however, important new information on the production dynamics is obtained. A systematic study of the production properties of these systems has been performed and it is found that these systems are not produced dominantly by double Pomeron exchange.Comment: 13 pages, Latex, 4 Figure

A study of pseudoscalar states produced centrally in pp interactions at 450 GeV/c

A study has been made of pseudoscalar mesons produced centrally in pp interactions. The results show that the eta and etaprime appear to have a similar production mechanism which differs from that of the pi0. The production properties of the eta and etaprime are not consistent with what is expected from double Pomeron exchange. In addition the production mechanism for the eta and etaprime is such that the production cross section are greatest when the azimuthal angle between the pT vectors of the two protons is 90 degrees.Comment: 11 pages, Latex, 3 Figure