Synopsis The Carn Chuinneag intrusion is a foliated granite pluton emplaced in the Moine rocks of the Northern Highlands of Scotland, containing large irregular inclusions of amphibolite. Minor sheet-like apophyses at the margin of the pluton extend into the Moine country rocks. The emplacement occurred after D 1 in static conditions and the Moinian envelope was distended. Structure contours suggest that the intrusion was originally a sheet-like pluton about 4 km (2.48 miles) thick. D 1 structures which are ubiquitous in the Moinian over a wide area surrounding the granite are entirely absent from the pluton. The widespread foliation of the pluton and sheet-like apophyses is equivalent to S 2 in the Moine rocks, and it is folded by major and minor scale D 3 folds closely similar in style to D 3 folds developed in the Moinian both inside and outside the granite aureole. D 4 deformed the whole of the pluton and its Moinian envelope. D 1 and D 2 structures of the Carn Chuinneag area and the Moine Thrust belt at Loch Eriboll are considered to be correlatives. Thus, pre-granite D 1 structures are inferred to be post-Arenig in age.
Summary The Carn Chuinneag granite comprises a suite of acid and subsidiary basic igneous rocks, intruded into the Moine of Easter Ross. Structural evidence indicates that the granite may have been sheet-like or laccolithic in form, and now occupies the core of a major D 3 synform. Hornfelsing of pelitic rocks in the aureole has preserved a variety of sedimentary structures. The former presence of andalusite and cordierite within the hornfels indicates that the granite was emplaced at a high structural level; their alteration to aggregates containing kyanite, may have resulted from burial of the area under the superincumbent load of the Ross-shire nappe during the second episode of deformation.
A pressure difference of 280 psi measured initially on opposite sides of themajor fault in the Hawkins Field led to pressure determinations in the Woodbinesand throughout the East Texas basin. Considering the large area, there isunusually good correlation between pressure losses and points of majorwithdrawals, these losses indicating that the basin pressure has beenmaterially reduced by withdrawals, primarily from the East Texas Field andsecondarily from the old fault-line fields of Limestone and Navarro counties, with the pressure loss varying inversely with the log of the distance fromthese two main areas of basin withdrawals to the measurement points. Apparentlyfaults located throughout the basin serve as local blocks to continuouspressure gradients. Introduction The pressure anomalies found in the Hawkins Field, Wood County, Texas, shortly after discovery have led to an area-wide investigation of the pressuredistribution within the Woodbine sand of the East Texas basin. These pressureswere obtained by drill-stem tests made for that sole purpose while drillingwildcat wells to deeper horizons. The Woodbine sand of Gulf Cretaceous Age isor has been productive of oil and gas in 42 different fields, with the 28 oilfields currently active having produced 118,000,000 bbl of oil during 1949.With one exception, producing energy for all Woodbine reservoirs has been from water drive provided predominantly by expansion of the tremendousvolume of water contained in the Woodbine sand. This producing mechanism wasrecognized at an early date and was described mathematically by Muskat and bySchilthuis and Hurst in 1934, and these principles were applied to the EastTexas Field performance by Buckley in 1938. Factual data on the pressure behavior in the Woodbine sand, especially inareas non-productive of oil, have been generally lacking, making estimates ofpressures at various points within the basin dependent upon mathematicalanalyses involving numerous assumptions. Such factual data have been gatheredand are now presented as possible aid to the industry in further analysis ofthe producing mechanism in tile Woodbine sand. T.P. 3000
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