Palaeocene Sandstones Research Articles

Unravelling the widening of the earliest Andean northern orogen: Maastrichtian to early Eocene intra‐basinal deformation in the northern Eastern Cordillera of Colombia

AbstractThe onset of deformation in the northern Andes is overprinted by subsequent stages of basin deformation, complicating the examination of competing models illustrating potential location of earliest synorogenic basins and uplifts. To establish the width of the earliest northern Andean orogen, we carried out field mapping, palynological dating, sedimentary, stratigraphic and provenance analyses in Campanian to lower Eocene units exposed in the northern Eastern Cordillera of Colombia (Cocuy region) and compare the results with coeval succession in adjacent basins. The onset of deformation is recorded in earliest Maastrichtian time, as terrigenous detritus arrived into the basin marking the end of chemical precipitation and the onset of clastic deposition produced by the uplift of a western source area dominated by shaly Cretaceous rocks. Disconformable contacts within the upper Maastrichtian to middle Palaeocene succession document increasing supply of quartzose sandy detritus from Cretaceous quartzose rocks exposed in eastern source areas. The continued unroofing of both source areas produced a rapid shift in depositional environments from shallow marine in Maastrichtian to fluvial‐lacustrine systems during the Palaeocene‐early Eocene. Supply of immature Jurassic sandstones from nearby western uplifts, together with localized plutonic and volcanic Cretaceous rocks, caused a shift in Palaeocene sandstones composition from quartzarenites to litharenites. Supply of detrital sandy fragments, unstable heavy minerals and Cretaceous to Ordovician detrital zircons, were derived from nearby uplifted blocks and from SW fluvial systems within the synorogenic basin, instead of distal basement rocks. The presence of volcanic rock fragments and 51–59 Ma volcanic zircons constrain magmatism within the basin. The Maastrichtian–Palaeocene sequence studied here documents crustal deformation that correlates with coeval deformation farther south in Ecuador and Peru. Slab flattening of the subducting Caribbean plate produced a wider orogen (>400 km) with a continental magmatic arc and intra‐basinal deformation and magmatism.

The Glenlivet gas discovery – an integrated exploration history

The Glenlivet gas discovery made by DONG E&P and partners (Faroe Petroleum and First Oil) in 2009 is one of the most recent discoveries in the offshore West of Shetland region. The exploration target was an amplitude-supported stratigraphic prospect, and the discovery well 214/30a-2 proved the pre-drill model by finding gas-bearing Late Palaeocene sandstones of excellent quality in the Vaila Formation. The exploration success challenged the exploration history of the Faroe-Shetland Basin, where a number of amplitude-driven stratigraphic prospects led to exploration failures in the 1990s. The prospect was identified by means of high quality 3D seismic data and improved petrophysical and seismic understanding combined with regional mapping of the Vaila Formation sandstones. A detailed sedimentological and biostratigraphic understanding of the Palaeocene succession, in conjunction with the above, helped to de-risk the prospect and led to successful drilling.

Podłoże i stratygrafia osadów czwartorzędowych w SW części Pojezierza Mazurskiego

W zbadanym obszarze w podlozu osadow czwartorzedowych wystepują liczne depresje i elewacje, ktorych powstanie jest prawdopodobnie związane z ruchami tektonicznymi, w mniejszym stopniu z deformacjami glacitektonicznymi. Osady czwartorzedowe zawierają osiem poziomow glin zwalowych: po dwa – zlodowacenia podlaskiego i krakowskiego, trzy – zlodowacenia środkowopolskiego i jeden – zlodowacenia baltyckiego. Lądolod zlodowacenia baltyckiego w czasie maksymalnego zasiegu zająl jedynie polnocną oraz zachodnią cześc terenu. SUBSTRATUM AND STRATIGRAPHY OF QUATERNARY DEPOSITS IN SOUTH-WESTERN MAZURY LAKELAND The studies have been carried through in the south-western part of the Mazury Lakeland situated in the upper Wkra and Drweca river drainage basins (Fig. 1). A small number of deep boreholes enabled an approximative only interpretation of topography of the bedrock composed of Maestrichtian marls and Lower Palaeocene sandstones (Fig. 2). The bedrock is distinctly inclined eastwards, with considerable elevations close to Żuromin and Ostroda and with a depression in Ilawa. Map of Quaternary substratum could be prepared with a greater accuracy (Fig. 3). One can easily find a set of deep depressions running from north-west to south-east. At both sides of these depressions substratum topography is quite different. To the south-west there are also deep depressions and aside them, just under the Quaternary deposits, there are Pliocene variegated clays. To the north-east, depressions are generally small and shallow but the whole area is formed mainly of brown coal formation. It makes an impression of “flooding” the previous topography of earlier Tertiary deposits by variegated clays. The present relief of Quaternary substratum is after all an effect of denudation as it is suggested by isolated patches of variegated clays in the northern area. Oligocene deposits occur in the Quaternary substratum mainly in depression bottoms. No examined interglacial sediments in the studied area made stratigraphy to be grounded on references to the surroundings, first of all to the Mlawa area. In the described region the Quaternary deposits are usually 70–l00 m thick and in the substratum depressions – even over 250 m. Generally, eight till horizons can be distinguished: two each of Cracovian (Mindel) and Podlasie (Gunz) glaciations, three of Middle-Polish (Riss) Glaciation and one – of Baltic (Wurm) Glaciation (Figs. 4 – 6). Three lowermost till horizons occur in substratum depressions only, the rest form already more or less continuous beds in a larger area. Some deposits of small rivers were also found; lack of larger rivers is caused by localization of the area in a watershed zone for most of Pleistocene. A more distinct, two-cyclic alluvial series in the western part of the area, was connected with Great (Holstein) Interglacial (Tab. 1); one-cyclic one close to Rybno – with an interglacistadial of Cracovian (Mindel) Glaciation (Fig. 6). The third, uppermost till horizon of Middle-Polish (Riss) Glaciation was referred to Mlawa Glacistadial. It forms vast morainic plateau in southern and south-eastern parts of the area (Fig. 7). On the plateau, there are fragments of fluvioglacial levels (fig. 8) and denuded end moraines, kames and eskers. Till horizon of Baltic (Wurm) Glaciation can be found only in the northern and western part of the area. Locally but especially in the south-western part on the area, this till series was removed by fluvioglacial erosion.

Irregular silica cementation in sandstones and its implication on the usability as building stone

Palaeocene sandstones outcropping in Western Spain have long been used for building purposes. Their use varies considerably: in some cities they have been the main stones used in the construction of buildings such as churches and cathedrals (Zamora), whereas in others, such as in the historic district of Salamanca, which has been a World Heritage site since 1988, they have been used in the lower part of the town's most striking monuments [two cathedrals (12th and 16th centuries), the Main Square (1755) and the House of Shells (15th century)] for protection against erosion and weathering, because they are more resistant than the Eocene sandstones used for the higher parts of the monuments. Although in some cases this solution has been successful, in others the results have been less satisfactory. Palaeocene sandstones have an important, although irregular, silica cement content. According to their uniaxial compression strength (UCS) they may be strong or very strong rocks, but under wet conditions some select samples display a significant decrease in their UCS. Furthermore, two types of opal cement can be found, one isotropic and the other birefringent, the former being the most efficient. Strength is even higher when isotropic opal cement is found together with alunite [ KAl 3 (SO 4 ) 2 (OH) 6 ].

Diagenesis and reservoir quality evolution of palaeocene deep-water, marine sandstones, the Shetland-Faroes Basin, British continental shelf

The Palaeocene, deep-water marine sandstones recovered from six wells in the Shetland-Faroes Basin represent lowstand, transgressive and highstand systems tract turbiditic sediments. Mineralogic, petrographic, and geochemical analyses of these siliciclastics are used to decipher and discuss the diagenetic alterations and subsequent reservoir quality evolution. The Middle-Upper Palaeocene sandstones (subarkoses to arkoses) from the Shetland-Faroes Basin, British continental shelf are submarine turbiditic deposits that are cemented predominantly by carbonates, quartz and clay minerals. Carbonate cements (intergranular and grain replacive calcite, siderite, ferroan dolomite and ankerite) are of eogenetic and mesogenetic origins. The eogenetic alterations have been mediated by marine, meteoric and mixed marine/meteoric porewaters and resulted mainly in the precipitation of calcite (δ 18O V−PDB=−10.9‰ and −3.8‰), trace amounts of non-ferroan dolomite, siderite (δ 18O V−PDB=−14.4‰ to −0.6‰), as well as smectite and kaolinite in the lowstand systems tract (LST) and highstand systems tract (HST) turbiditic sandstone below the sequence boundary. Minor eogenetic siderite has precipitated between expanded and kaolinitized micas, primarily biotite. The mesogenetic alterations are interpreted to have been mediated by evolved marine porewaters and resulted in the precipitation of calcite (δ 18O V−PDB=−12.9‰ to −7.8‰) and Fe-dolomite/ankerite (δ 18O V−PDB=−12.1‰ to −6.3‰) at temperatures of 50–140 and 60–140 °C, respectively. Quartz overgrowths and outgrowth, which post- and pre-date the mesogenetic carbonate cements is more common in the LST and TST of distal turbiditic sandstone. Discrete quartz cement, which is closely associated with illite and chlorite, is the final diagenetic phase. The clay minerals include intergranular and grain replacive eogenetic kaolinite, smectite and mesogenetic illite and chlorite. Kaolinite has been subjected to mesogenetic replacement by dickite. The K-feldspar and plagioclase grains have been albitized. Dissolution of calcite cement and of framework grain (feldspar, volcanic fragments and mud intraclasts) has resulted in a considerable enhancement of reservoir quality.

The Maureen Field, Block 16/29a, UK Central North Sea

abstract The Maureen field comprises the Maureen, Mary and Morag Accumulations, the reservoirs being Palaeocene Sandstones, Upper Jurassic sandstones and Permian dolomites respectively. The field lies about 10 km NNE of the Moira Palaeocene field. Maureen was discovered in 1973, came on-stream in 1983 and produced 217.4 MMBBL (from an estimated STOIIP of 397 MMBBL). The field ceased production in October 1999. It is trapped in a four-way dip closure over a salt dome and scaled by the overlying Lista Formation mudstones. The reservoir is up to 450 ft gross thickness, with core porosity from 18-28% and good sand connectivity. Morag was discovered in 1979. came on-stream in 1991 and produced 2.6 MMBBL before being shut-in in 1994. It produced from clean fractured dolomites in a stratigraphic trap. Mary was discovered and came on-stream in 1991. The initial well died after 1 year. A later well was put on-stream in 1997. Mary produced 2.83 MMBBL before final shut-in in June 1999. Reservoir quality is reasonable, but sand distribution is problematic. All the oils are sourced from the Kimmeridge Clay formation on the adjacent Maureen Shelf area.

High resolution geochemical and petrographical correlation of deep marine Palaeocene sandstones from the Foinaven Field, West of Shetland

Cores from three wells in the Upper Palaeocene deep-marine reservoir interval of the Foinaven Field, West of Shetland have been analysed using trace element geochemistry and petrography. The 60 m thick turbidite-dominated succession is restricted to the T34 biozone and comprises a series of seismically defined channel and overbank deposits. Petrographic and trace element geochemical data indicate that wells 204/24a-3 and 204/25b-5 have strong similarities and that strata in the remaining well (204/24a-7) have distinctly different signatures. Of the two related wells, 204/25b-5 is dominated by a thick amalgamated sandstone succession, 204/24a-3 by more thinly bedded and finer grained sandstones considered to represent channel and associated overbank deposits respectively. Similarities in geochemical and petrographic data allow division of the biozone in the two related wells into four principal correlation zones with two additional sub-zones. The study has established a high resolution correlation scheme and constrained correlation lengths for reservoir and non-reservoir facies in a deep marine depositional system.

Central North Sea overpressures: insights into fluid flow from one- and two-dimensional basin modelling

Abstract Jurassic and Triassic reservoirs in the Central North Sea are highly overpressured (>40 MPa above hydrostatic pressure). Simulation of the interplay between rapid Tertiary subsidence, seal permeability and fluid flow allows insight into the geological controls on the distribution and magnitude of the overpressure. One-dimensional models demonstrate that, unlike other basins, the overpressure developed in the Graben is not determined by the thickness and permeability of the shale pressure seal. A two-dimensional model simulating lateral flow beneath the pressure seal provides an accurate simulation of the overpressure distribution. Disequilibrium compaction of shale-dominated off-structure regions forms the principal overpressuring mechanism. Lateral flow in the permeable Fulmar sandstones leads to high overpressure and focused vertical escape on an axial high, where the seal is thinner above a subcropping Fulmar Fm. A layered hydrogeological regime is suggested, with shallow Tertiary pressure cells separated from deep Cretaceous-Triassic pressure cells by normally pressured, permeable Palaeocene sandstones. The pre-Cretaceous rift-associated configuration of the Graben, in combination with 3 km of Tertiary subsidence, controls the distribution of overpressure.

Pressure cells and pressure seals in the UK Central Graben

The Central Graben of the North Sea is characterised by high levels of overpressure (up to 40 MPa overpressure at 4500 m depth). We present pressure data for Cenozoic and Mesozoic reservoirs. Palaeocene sandstones control pressures in Tertiary mudstones and Cretaceous Chalk by acting as a regional ‘drain’. We divide the Jurassic into 18 pressure cells. The rift structure of the Graben controls the magnitude of pressure in each cell. Lateral hydraulic communication exists over 10 km distance between deeply-buried terraces (> 5000 m depth) and shallow structural highs (< 4500 m depth). Lateral communication increases pressure in the structurally-elevated sandstones to the minimum stress. This dynamic process produces zones of vertical fluid flow on the Forties-Montrose High, termed Leak Points. Vertical flow at Leak Points produces a 20 MWm −2 heat flow anomaly and controls hydrocarbon retention. Leak Points are water-wet, while deep terraces in hydraulic communication with Leak Points are condensate-bearing. The Kimmeridge Clay Fm. forms the pressure seal in deep terraces.

The Forties Field - 20 Years Young

Summary This paper describes how the development of the Forties field has evolved over the past 20 years; the current issues and activities; and the direction for the future. Introduction In October 1970, BP' s semi-submersible drilling rig SeaQuest struck oil in Upper Palaeocene (Tertiary) sandstones of UKCS Block 21/10 (Figure 1). Four appraisal wells were drilled in 1970 and 1971, which delineated a large oil reservoir at a depth of 2135 metres, covering an area of 93 km2. The maximum thickness of the oil-bearing sandstone was estimated at 187 metres. Reserves were calculated to be 1800 mmstb from an oil-in-place of 4600 mmstb, and production was projected to continue until the year 2000. In 1971 Shell/Essodrilled a successful well, 22/6-1, which demonstrated the south-eastern extension of the field into Block 22/6. The field is a four way dip closed anticline which overlies the Forties-Montrose Ridge and is situated close to the junction of the Central, South Viking and Witch Ground Grabens (Figure 2). The reservoir occurs in thick Upper Palaeocene sandstones deposited as a major sand-rich submarine fan sequence. The field is underlain by a large active aquifer. The development plan evolved during 1972-75. The first major oil field development in the North Sea, it comprised four fixed steel drilling/production platforms, installed in Block 21/10 in 1974 and 1975, with a total capacity for108 wells, a production system capable of handling 500 mbd of oil, later increased to 600 mbd, with 100 mbd of produced water, and a sea water injection system with a capacity of 600 mbd. A schematic diagram of the production system is shown in Figure 3. Development drilling began in June 1975 and production started on 12th September 1975. Plateau production of 500 mbd was reached in1978 and lasted until 1981. A fifth platform, smaller and without processing facilities, was added over the south-eastern extension (South East Forties -SEF) during 1985, with production beginning in March 1987. For more detail on the reservoir reasoning behind the original development scheme see Reference1. Forties is currently producing 111 mbd, the field water cut has only recently passed 60% and 90% of the reserves have been produced. Reservoir Management Reservoir performance has been characterised by excellent vertical sweep through clean sands by the underlying, very mobile aquifer, supported by peripheral sea water injection. There are sufficient permeability restrictions between the three parts of the field, namely SEF, the Main Sand and the Charlie Sand, to cause significant pressure differences between them (Figure 4). Other localised isolated regions have been identified in the FD area during recent infill drilling. The management of the reservoir has been based on treating the three regions separately in terms of pressure support requirements. The primary thrust of reservoir management, common to all areas, has been to track the movement of water within the field to maximise vertical and areal sweep. This has been achieved by performing water shut-off when advantageous to oil flow rate, applying artificial lift when possible, and targeting infill wells at poorly swept areas. With the onset of sea water breakthrough in production wells, bariumsulphate scale deposition has increased in down-hole tubulars and surface facilities (Reference 2). Extended life scale inhibitor squeeze treatments into the formation have been required to inhibit scale deposition. Calcium carbonatescale has also been a problem in gas lifted wells. Generally the deposition of scale is inhibited, but in some cases inhibitor deployment has not been successful. Acid (for carbonate) or chelator treatments have had limited success, while in severe cases wells have been successfully restored to production by milling with coiled tubing (Reference 3).

The Maureen Field, Block 16/29a, UK North Sea

Abstract The Maureen Oilfield is located on a fault-bounded terrace in Block 16/29a of the UK Sector of the North Sea, at the intersection of the South Viking Graben and the eastern Witch Ground Graben. The field was discovered in late 1972 by the 16/29-1 well, and was confirmed by three further appraisal wells. The reservoir consists of submarine fan sandstones of the Palaeocene Maureen Formation, deposited by sediment gravity flows sourced from the East Shetland Platform. The Palaeocene sandstones, ranging from 140 to 400 ft in thickness, have good reservoir properties, with porosities ranging from 18-25% and permeabilities ranging from 30-3000 md. Hydrocarbons are trapped in a simple domal anticline, elongated NW-SE, which was formed at the Palaeocene level by Eocene/Oligocene-aged movement of underlying Permian salt. The reservoir sequence is sealed by Lista Formation claystones. Geochemical analysis suggests Upper Jurassic Kimmeridge Clay shales have been the source of Maureen hydrocarbons. Estimated recoverable reserves are 210 MMBBL. Twelve production wells have been drilled on the Maureen Field. A further seven water injection wells have been drilled to maintain reservoir pressure.

The Forties Field, Block 21/10, 22/6a, UK North Sea

Abstract The Forties Field is located 180 km (112 miles) ENE of Aberdeen, predominantly in UK Licence Block 21/10. It was discovered in 1970, when an exploration well encountered hydrocarbons in Palaeocene sandstone within an anticlinal structure. Four appraisal wells confirmed the existence of a major oilfield, with an area of approximately 90 sq km (35 sq miles) at a depth of approximately 2000 m (6500 ft). The reservoir occurs in thick Late Palaeocene sandstones deposited in two major sand-rich submarine fan sequences. The field has been producing oil since September 1975. Stock Tank Oil Initially in Place (STOIIP) has been calculated as 4343 MMBBL, and original reserves estimated as 2470 MMBBL, representing an overall recovery of 57%. The field came off plateau production of 500 000 BOPD in 1981, and by mid-1989 production had declined to about 250 000 BOPD. After fourteen years production, the field has produced more than 2 billion STB. Remaining reserves are about 500 MMBBL which includes recovery via artificial lift. Field life has been projected to extend beyond the year 2000. Water injection into the aquifer commenced in 1976, and continues at the present day at an average rate of 390 000 BWPD. There is also a significant contribution to pressure support from the underlying aquifer. At present there are 103 available wells in the field, 81 producers and 22 injectors.

THE PROVENANCE AND DISTRIBUTION OF THE PALAEOCENE SANDS OF THE CENTRAL NORTH SEA

A study of the detrital heavy minerals from Palaeocene sandstones of the central North Sea basins has revealed that variations exist which cannot be explained in terms of varying conditions either during or after deposition, and therefore reflect the influence of distinct source areas. Four sand bodies have been defined on a mineralogical basis, two of which occur in the Central Graben and southern Viking Graben, derived from the E. Shetland Platform, the other two being developed in the Moray Firth area, derived from the Scottish landmass. These sand bodies, when related to the existing lithostratigraphic framework, define four phases of basin subsidence, with the sand depocentre alternating between the Central Graben and the Moray Firth basin. This oscillation in basin subsidence, the association with volcanogenic sediments and the apparent basement control on distribution of sands in the Moray Firth indicate a degree of tectonic control hitherto undescribed for the Palaeocene of the area.Studies of sandstones in or around the inferred source areas have revealed that the metamorphic basement was the major contributor to the sands of the Moray Firth, rather than the pre‐existing sandstones of Devonian, Permo‐Trias or Jurassic ages which occur on the margins of the Firth. Likewise the Old Red Sandstone or Permo‐Trias sandstones of the East Shetland Platform are not suitable source rocks for the sands of the Central Graben and in this case it has been necessary to postulate the existence, at least until the end of Palaeocene times, of Carboniferous sands on the Platform. Such sands in the central North Sea have been shown to possess a mineralogy not dissimilar from that of the Palaeocene sands in question.

Depth Control of Intrastratal Solution of Heavy Minerals from the Palaeocene of the North Sea

ABSTRACT Several detrital heavy mineral species from Palaeocene sandstones of the central North Sea basin show surface features attributable to chemical etching. Garnet, staurolite, and kyanite, selected for study because of their basinwide distribution, show an increase in intensity of these etch features with depth, with staurolite and kyanite grains becoming skeletal. The latter two minerals also show a parallel decrease in abundance with depth, ultimately disappearing from the assemblage, staurolite around 8500 (2590 m) and kyanite around 7000 (2135 m). This trend is interpreted as being the result of increasing intrastratal solution with depth.