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Multidisciplinary exploration strategy in the northeast Netherlands Zechstein 2 Carbonate play, guided by 3D seismic
Abstract
The Nederlandse Aardolie Maatschappij has actively pursued the exploration of the Zechstein 2 Carbonate play over the last 40 years. The effort concentrated largely on the SE Drenthe area. It has resulted in the discovery of 20 gas fields with cumulative reserves of some 57 x 109m3. The Zechstein 2 Carbonate Member is part of the Basal Zechstein Unit which developed mainly as an anhydrite platform at the southern fringe of the Southern Permian Basin. The facies within the member reflect platform, slope and basinal settings. The subsurface data collected in the exploration and development of the Zechstein fields have led to a detailed sedimentological model for the member.Prospects in the member are seismically defined as structural highs at Top Zechstein 2 Anhydrite level. However,as exploration moves towards the search for more subtle traps, 3D seismic becomes indispensable. Basal Zechstein isochore maps based on 3D seismic, display the topography of the Basal Zechstein platform. These maps are used to assess reservoir potential and gross reservoir thickness. Variations in reservoir parameters, especially porosity, of the Zechstein 2 Carbonate Member are reflected in the seismic response. Quantitative studies based on 3D seismic allow spatial prediction of specific reservoir parameters. Detailed fracture studies in gas fields have demonstrated a relationship between seismically detectable fault patterns and core-scale reservoir enhancing fracture patterns. The Collendoornerveen exploration well demonstrates the successful integration of the various disciplines.
... As a result, a connection was established between the Southern Permian Basin and the Barents Sea. The Saalian and Altmark pulses influenced the distribution of basal Upper Rotliegend sands (Van der Baan, 1990; Van de Sande et al., 1996; NITG, 1998). The Tubantian II pulse is thought to be of compressional origin and related to the Uralian orogeny (Geluk, 2005 ), and marks the second, final , consolidation of Pangea at the end of the Permian (Vai, 2003). ...
... The southern limit of the Z2 Carbonate (or Main Dolomite) lies considerably more to the north compared to the Z1 Carbonate (cf.Figs 13, 16). Within the Z2 Carbonate, three facies realms can be identified: platform , slope and basin (Van de Sande et al., 1996; Geluk, 72 Permian > M.C. Geluk 2000). ...
... These rocks have source rock potential, with a total organic-carbon content of up to 1.2% (Lokhorst, 1998). In the vicinity of the carbonate platforms, slumps and turbidites of displaced shelf deposits have been identified (Garoussi & Taylor, 1992; Van de Sande et al., 1996 ). The slope facies consists of light-coloured limestones and dolomites, and of platform sediments redeposited by mass flows. ...
Permian deposits in the Netherlands are represented by the Lower Rotliegend, Upper Rotliegend and Zechstein groups. The Lower Rotliegend Group (Middle Permian), of volcanic origin, is present only locally. The Upper Rotliegend and Zechstein groups, Middle
to Late Permian in age and deposited under warm and arid climatic conditions, are present throughout most of the Netherlands. The Upper Rotliegend Group represents fluvial, eolian and playa-lake deposits, with the lake situated in the northern offshore area. The Zechstein
Group comprises a series of marine evaporites and carbonates, which show a gradual retreat of the sea during its deposition. By the end of this deposition, continental and more humid conditions had returned. The depositional thickness of the Permian reaches almost 2000 m
in the northern offshore. The regional unconformity at the base of the Permian represents in most places a hiatus of 40 to 60 Ma. The Permian deposits contain more than 95% of the large reserves of natural gas in the Netherlands; they also contain exploitable rock salt and potassium-magnesium salts. The thick layer of Zechstein rock salt deformed into a large number of salt pillows and diapirs, and strongly influenced the post-Permian structural development of the country.
... As a result, a connection was established between the Southern Permian Basin and the Barents Sea. The Saalian and Altmark pulses influenced the distribution of basal Upper Rotliegend sands (Van der Baan, 1990; Van de Sande et al., 1996; NITG, 1998). The Tubantian II pulse is thought to be of compressional origin and related to the Uralian orogeny (Geluk, 2005 ), and marks the second, final , consolidation of Pangea at the end of the Permian (Vai, 2003). ...
... Figs 13, 16). Within the Z2 Carbonate, three facies realms can be identified: platform , slope and basin (Van de Sande et al., 1996; Geluk, 72 Permian > M.C. Geluk 2000). ...
... These rocks have source rock potential, with a total organic-carbon content of up to 1.2% (Lokhorst, 1998). In the vicinity of the carbonate platforms, slumps and turbidites of displaced shelf deposits have been identified (Garoussi & Taylor, 1992; Van de Sande et al., 1996 ). The slope facies consists of light-coloured limestones and dolomites, and of platform sediments redeposited by mass flows. ...
Permian deposits in the Netherlands are represented by the Lower Rotliegend, Upper
Rotliegend and Zechstein groups. The Lower Rotliegend Group (Middle Permian), of
volcanic origin, is present only locally. The Upper Rotliegend and Zechstein groups, Middle to Late Permian in age and deposited under warm and arid climatic conditions, are present throughout most of the Netherlands. The Upper Rotliegend Group represents fluvial, eolian and playa-lake deposits, with the lake situated in the northern offshore area. The Zechstein Group comprises a series of marine evaporites and carbonates, which show a gradual retreat of the sea during its deposition. By the end of this deposition, continental and more humid conditions had returned. The depositional thickness of the Permian reaches almost 2000m in the northern offshore. The regional unconformity at the base of the Permian represents in
most places a hiatus of 40 to 60 Ma. The Permian deposits contain more than 95% of the
large reserves of natural gas in the Netherlands; they also contain exploitable rock salt and potassium-magnesium salts. The thick layer of Zechstein rock salt deformed into a large number of salt pillows and diapirs, and strongly influenced the post-Permian structural development of the country.
... In 1948, the Nederlandse Aardolie Maatschappij (NAM, a subsidiary of SIPM and Esso) ing most Zechstein-2 Carbonate Member (ZEZ2C) gas fields and some other fields, and the existing 3-D seismic coverage (reproduced, with permission from Springer Verlag, from: Van de Sande et al., 1996). ...
... Generalised stratigraphy of the NE Netherlands, detailing the 'Basal Zechstein Unit', an informal unit in the Zechstein Group, of which the further subdivision is shown in Figure 3 (reproduced, with permission from Springer Verlag, from Van de Sande et al., 1996). ...
... The main dolomite unit may reach locally a thickness of 120 m. Detailed 3-D seismic data have revealed complex platform outlines, isolated off-platform highs and intra-platform basins ( Van de Sande et al., 1996). The facies distribution of the ZEZ2C Carbonate Member was largely controlled by the palaeo-relief of the ZEZ1A Anhydrite Member that formed a platform (Figs 5B, 6 and 8). ...
Hydrocarbon exploration in The Netherlands has a chequered history from
serendipitous oil shows via chance oil/ gas discoveries to finding the
largest continental European oil field in 1943, followed by finding the
largest gas field in the world in 1959. The present contribution traces
the development of moderate to good porosity/permeability trends in
depositional facies of Zechstein Stassfurt carbonates in a ‘gas
play’ intermediate in significance between the above two plays but
all in the northern part of The Netherlands. Various depositional facies
in the Stassfurt carbonates were turned into ‘carbonate fabric
units’ by diagenetic processes creating or occluding the
porosity/permeability. This formed moderate to good gas reservoirs in
barrier-shoal, open-marine shelf and proximal-slope carbonates in the
subsurface of the province of Drenthe in the NE Netherlands. The
diagenetic models forming these carbonate fabric units are linked to the
variety of facies in a depositional model which shows explain and
predicts the reservoir trends. Such depositional/diagenetic facies are
‘translated’ into characteristic petrophysical values
recognisable on wire line logs in uncored wells, and in characteristic
seismic expressions that show these trends in undrilled areas. This
approach has been proven to be effective in delineating porosity trends,
visualised by 3-D seismic in the Collendoornerveen field, and thus
provides a new exploration ‘tool’ in hydrocarbon exploration
.
... This study reports conventional triaxial deformation experiments performed on anhydrite rock from the base of the Permian Zechstein sequence [Van de Sande et al., 1996], which caps many depleted gas reservoirs and potential CO 2 storage sites in the Netherlands and the North Sea. Our aim was to determine the mechanical behavior and damage characteristics of this material and to assess if there are any mechanical or chemically coupled effects of CO 2 -charged pore fluid that might threaten integrity as angle of up to 60° to the sample axis. ...
... The nature and suggested rate for reaction (5) imply that for simple CO 2 penetration by reaction with a static pore fluid (no long-range advective transport), the resulting penetration depth would be approximately 30 cm in 1000 years and ~3 m in 10000 years. For an anhydrite formation of 50 m thick, such as the Zechstein [ Van de Sande et al., 1996], this amounts to 0.6-6% penetration. In practice, this represents an upper bound, as the reaction will undoubtedly slow down as the reaction front advances into the anhydrite. ...
... The K12-B reservoir is a depleted gas reservoir overlain by Zechstein anhydrite caprock. Following geological data [Van de Sande et al., 1996;Van der Meer et al., 2006b], we take the sandstone reservoir and the anhydrite member at the base of the Zechstein to be 150 and 50 m thick respectively, with the reservoir-caprock interface located at a depth of ~3800 m (see Figure 12a). Though the K12-B reservoir is oval in plan view (5 km × 8.5 km), we consider a circular reservoir with a diameter of 10 km, and overlain by a disc-shaped plate of caprock. ...
Maintaining caprock integrity is prerequisite for geological storage of CO2. We investigated the mechanical strength and damage behavior of anhydrite-rich caprock, which seals many potential CO2 storage sites around the world. Conventional triaxial tests were performed at temperatures of 20°C–80°C, confining pressures of 1.5–50 MPa and strain rates of ∼10−5 s−1. We determined the failure and dilatation envelopes for dry anhydrite and studied the effect upon strength and dilatation of high-pressure pore fluids (Pf = 15 MPa), namely presaturated CaSO4 solution and CO2-saturated CaSO4 solution. For dry samples, we observed an increase in strength with confining pressure and a slight weakening with temperature. Fluid penetration prior to failure resulted in a direct effective pressure effect on strength, but not on volumetric behavior. Fluid penetration during failure is too slow to influence mechanical and volumetric behavior. Overall, we found no short-term chemical effects of CO2 and pore fluid on the strength of anhydrite. Penetration of the samples by CO2-saturated pore fluid was more effective than by solution alone, most likely as a result of the lower interfacial tension of the CO2/water system. Simple analytical calculations based on the elastic flexure of a seal formation, combined with our failure and dilatation envelopes, show that, for realistic conditions, caprock integrity will not be compromised by mechanical damage. In addition, long-term chemical reactions of anhydrite with CO2 will most likely not lead to significant CO2 penetration, though more research is needed.
... The Zechstein in the Netherlands was the subject of several papers. Visser (1955), Brueren (1959), Van Adrichem Boogaert & Burgers (1983), Clark (1986), Van der Poel (1987, Van der Baan (1990), Van der Sande et al. (1996), Geluk et al. (1996Geluk et al. ( , 1997 and Geluk (1999) presented details on the sedimentology, paleogeography, reservoir development and tectonics. The stratigraphic framework of the Zechstein has been published by Van Adrichem Boogaert & Kouwe (1993-1997. ...
... ( Fig. 5).This is commonly recognised throughout the Southern Permian Basin (Sannemann et al., 1978;Cameron et al., 1992;Strohmenger et al., 1996a;Taylor, 1998) and reflects the progradational or aggradational infill of the basin (Clark, 1986;Van der Sande et al., 1996).This sigmoidal shape is caused by a thinning of the carbonate unit on both the landward and the basinal side, with a maximum thickness development on the carbonate slope or the transition to the platform. In the Zl Carbonate Member, local disturbances of this generalised isopach pattern occur, suggested to be the effect of synsedimentary tectonics (M.A. Ziegler, 1989;Geluk, 1999). ...
... The facies map of the Z2 Carbonate Member (Fig. 7) has been constructed based upon publications and well data. The map of the eastern Netherlands was adopted from the publication by Van der Sande et al. (1996), and is based upon 3-D seismic data (Fig. 3). Outside this area, the map is based upon well data. ...
The Late Permian Zechstein carbonates in the Southern Permian Basin were deposited under marine conditions. The carbonates form part of a largely progradational infill, with a gradual northward facies shift. The paleogeography of the Zechstein carbonate deposits has been reviewed recently on the base of well data, cores and publications. This has resulted in three updated maps of the carbonate units. These maps reflect the increase in knowledge of the palaeogeography of the Zechstein as a result of several decades of subsurface exploration. It is found that deposition of the carbonates was controlled by various factors, i.e., rifting during deposition of the basal Zechstein, sea-level fluctuations and basin subsidence. This resulted in an overall E-W orientated facies distribution in the Zechstein carbonates, and in the gradual northward shift of the various facies belts in time.
Reefs in the Zl Carbonate Member and off-platform highs and turbidites in the Z2 Carbonate Member have been identified as potential future exploration targets.
... This windward orientation of the margin facilitated the development of high-energy ooidal shoals that characterise the (Z2) Hauptdolomit Formation stratigraphy. Oolite grainstones observed in the Hauptdolomit Formation core from well 47/18-1, and large-scale hummocky cross-stratification, with southwest-directed palaeocurrent directions documented in Zechstein (Z1) oolite shoal deposits exposed onshore in Yorkshire (Kaldi, 1986a), provide strong evidence that development of the margin in this area was also strongly influenced by onshore directed trade winds, which are consistent with published facies models for Zechstein (Z1-Z2) carbonate margins (Van de Sande et al., 1996). It therefore seems highly likely that the development of the resultant Z2 shelf-margin in the study area palaeomorphology was controlled by tectonically-linked slope failure enhanced by protracted onshore-directed storm wind-and wave-action. ...
... The morphology of the Z2 margin in the study area is consistent with the findings from equivalent strata in other parts of the SPB. Comparable features and margin palaeomorphology of embayments and promontories have been mapped equivalent Zechstein facies elsewhere in the SNS subsurface from seismic to the south of the MNSH, in Quadrants 36, 37, 42 and 43 (Patruno et al., 2017), as well as in the Netherlands subsurface from the mapping of the Basalanhydrit Formation using onshore seismic data ( Van de Sande et al., 1996), and beyond (e.g. Germany and Poland; Ziegler, 1989;Strohmenger et al., 1996;Geluk, 1999;Wagner, 2004;Jaworowski and Mikołajewski, 2007;Kotarba and Wagner, 2007;Słowakiewicz and Mikołajewski, 2009). ...
Seismic interpretation, geological mapping and depth conversion of the Zechstein Supergroup (Z2 cycle), using high-quality well-calibrated three-dimensional (3-D) seismic, has revealed the complex palaeomorphology of a deeply-buried ancient carbonate shelf-margin on the southwestern margin of the Southern Permian Basin. The new mapping shows that the margin comprises a series of corrugated embayments and promontories which extend up to 5 km (3 mi) into the basin and locally have a palaeobathymetric relief of >200 m (650 ft). Well calibration across the margin demonstrates a strongly bipartite lateral thickness distribution between a high velocity anhydrite-dominated shelf and a lower velocity halite-dominated basin. Strong lateral and vertical velocity variations in the Upper Permian Zechstein Supergroup are known to have major impacts upon seismic imaging and depth conversion in the SPB. The resulting uncertainty remains one of the major challenges when interpreting and assessing the prospectivity of the underlying Upper Permian, Rotliegend Group (Leman Sandstone Formation) reservoirs in the UK Southern North Sea. An understanding of the Zechstein shelf edge's 3-D physiography and its velocity variation has implications for the delineation of traps containing the prospective reservoirs that lie below. Recognition of the complexity and effects of this shelf-margin contributed to the recent Juliet Discovery whose position outside of the presently defined Rotliegend Group play fairway suggests that prospectivity is more extensive along the basin margin than previously thought. As such, the work provides a means by which to identify and delineate new structures and extend the life of this mature yet prolific gas province.
... For example, the principal cap rocks of oil and gas reservoirs in the Middle East such as Iran, Iraq, Qatar, and Saudi Arabia (Alsharhan and Nairn, 2003), Dongping field in the Qaidam Basin, China (Ma et al., 2018), Algeria, Netherlands and USA (Grunau, 1987) are made of anhydride mineral. There are many CO 2 potential storage sites in the North Sea and Netherland that are overlaying by anhydride rocks (van de Sande et al., 1996). Moreover, anhydride lithotype shows potential for storage of radioactive waves in the USA (Dean and Johnson, 1989). ...
This study investigates the effect of stress magnitude and stress history on porosity and permeability values of anhydride and carbonate rocks. Porosity and permeability properties are measured for twelve anhydride and carbonate core samples under stress loading and unloading conditions. The results of permeability measurements show that tighter core samples are more stress dependent while the anhydride samples are generally more sensitive to the stress. The gap between stress loading and unloading (hysteresis) is more considerable at lower effective stress values. The results also indicate that the hysteresis is more noticeable in the anhydride core samples. The gas slippage factor is also determined which specifies the flow channels systems of rocks. Three different flow channels systems are observed in the anhydride core samples while the carbonate core samples show one flow channels system. Porosity measurements show that, it has less sensitivity to the effective stress for both anhydride and carbonate core samples.
... Gas and oil from Zechstein reservoirs are mainly produced from either Z2 or Z3 carbonates, whilst the seal is provided by overlying salts. Exploration focus has traditionally been on the porous oolite belts within the Z2 and Z3 carbonates (Van der Baan 1990; Van de Sande et al. 1996), which run approximately East-West, parallel to the southern border of the basin. These oolite belts have good primary reservoir properties, which may be enhanced by diagenetic leaching and early charging (Van der Baan 1990). ...
The Southern North Sea Basin area, stretching from the UK to the Netherlands, has a rich hydrocarbon exploration and production history. The past, present and expected future hydrocarbon and geothermal exploration trends in this area are discussed for eight key lithostratigraphic intervals, ranging from the Lower Carboniferous to Cenozoic. In the period between 2007 and 2017, a total of 95 new hydrocarbon fields were discovered, particularly in Upper Carboniferous, Rotliegend and Triassic reservoirs. Nineteen geothermal systems were discovered in the Netherlands onshore, mainly targeting aquifers in the Rotliegend and Upper Jurassic/Lower Cretaceous formations. Although the Southern North Sea Basin area is mature in terms of hydrocarbon exploration, it is shown that with existing and new geological insights, additional energy resources are still being proven in new plays such as the basal Upper Rotliegend (Ruby discovery) for natural gas and a new Chalk play for oil. It is predicted that hydrocarbon exploration in the Southern North Sea Basin area will probably experience a slight growth in the coming decade before slowing down, as the energy transition further matures. Geothermal exploration is expected to continue growing in the Netherlands onshore as well as gain more momentum in the UK.
... Gas fields producing from the Zechstein occur in the Lower Saxony Basin in the east, and the Central Netherlands Basin in the west of the Netherlands (Fig. 16). The reservoirs are platform carbonates that developed along the southern margin of the Southern Permian Basin, and that are sealed by Zechstein salt and anhydrite (Van der Baan, 1990; Van de Sande et al., 1996;Geluk, this volume). The traps are predominantly fault-dip closures, with some four-way dip closures. ...
... Gas fields producing from the Zechstein occur in the Lower Saxony Basin in the east, and the Central Netherlands Basin in the west of the Netherlands (Fig. 16). The reservoirs are platform carbonates that developed along the southern margin of the Southern Permian Basin, and that are sealed by Zechstein salt and anhydrite (Van der Baan, 1990; Van de Sande et al., 1996;Geluk, this volume). The traps are predominantly fault-dip closures, with some four-way dip closures. ...
A great variety of proven hydrocarbon plays and trap styles are present in the sedimentary succession of the Netherlands, which starts in the Middle Paleozoic and has been deformed by several periods of structurations. The thick Permian Zechstein salt in much of the subsurface provides an effective seal between a prolific Paleozoic gas system and a mixed, Mesozoic, gas and oil-prone hydrocarbon system. The giant Groningen gas field represents two- thirds of the Dutch recoverable gas reserves.it contained an initially recoverable gas volume of ca. 2700 BCM in thick, mainly fluvial sandstones of the Permian Upper Rotliegend. The Rotliegend play is formed by a near-ideal superposition of i) thick westphalian successions with abundant coal layers as source rock for gas, ii) thick Upper Rotliegend sandstones as reservoir, and iii) the thick Zechstein salt as seal.
Triassic plays are second in terms of proven volumes. Additional gas reserves are in Zechstein Carbonates, westphalian sandstones and Cretaceous sandstones, as well as Upper Cretaceous Chalk and unconsolidated Tertiary and Quarternary sands. Producible oil occurs within the Late Jurassic and Early Cretaceous rift basins in a variety in sandstone reservoirs and trap styles. Only minor amounts of oil have so far been found in Upper Cretaceous Chalk reservoirs. The exploration of the Dutch subsurface is in a mature stage. Yet, new discoveries continue to be made, and assessment of the remaining volumes show that significant volumes, mainly of gas, are yet to be made.
... Gas fields producing from the Zechstein occur in the Lower Saxony Basin in the east, and the Central Netherlands Basin in the west of the Netherlands (Fig. 16). The reservoirs are platform carbonates that developed along the southern margin of the Southern Permian Basin, and that are sealed by Zechstein salt and anhydrite (Van der Baan, 1990; Van de Sande et al., 1996;Geluk, this volume). The traps are predominantly fault-dip closures, with some four-way dip closures. ...
A great variety of proven hydrocarbon plays and trap styles are present in the sedimentary
succession of the Netherlands, which starts in the middle Paleozoic and has been deformed by several periods of structuration. The thick Permian Zechstein salt in much of the subsurface provides an effective seal between a prolific Paleozoic gas system and a mixed, oil and gas-prone Mesozoic hydrocarbon system. The giant Groningen field represents two thirds of the recoverable Dutch gas reserves. It contained an initially recoverable gas volume of ca. 2700 × 109 m3 in thick, mainly fluvial sandstones of the Permian Upper Rotliegend Group. The Rotliegend play is formed by a near-ideal superposition of i) the thick Upper Carboniferous, Westphalian succession with abundant coal measures as source rocks for gas, ii) good Rotliegend reservoir sandstones, and iii) the excellent seal of the Zechstein salt. Triassic plays are second in importance with respect to proven gas volumes. Additional gas reserves are in Permian Zechstein carbonates, Jurassic and Cretaceous sandstones, Upper Cretaceous chalk as well as in shallow unconsolidated sands of Tertiary and Quaternary age. Producible oil occurs within the Late Jurassic and Early Cretaceous rift basins in a variety of sandstone reservoirs and trap styles. Only minor amounts of oil have so far been found in the Upper Cretaceous chalk. The exploration of the Dutch hydrocarbon plays is in a mature stage. Yet, new discoveries continue to be made, and assessments of remaining potential show that significant volumes, in particular of gas, are yet to be found.
... Evaporites, and especially anhydrite, form an important seal for many hydrocarbon reservoirs across the world, as well as for several CO 2 injection pilot sites (e.g. the Weyburn Field, Canada [12,13]; the K-12B Field, the Netherlands [14]). In the Netherlands and the North Sea, many depleted gas reservoirs and potential CO 2 storage sites are capped by the basal anhydrite of the Permian Zechstein evaporite sequence [14,15]. However, lateral variations in mineralogical composition and texture may occur within the anhydrite unit. ...
We investigated the effect of rock texture and composition on the mechanical strength and volumetric behaviour of anhydrite-rich caprock. Conventional triaxial experiments were performed at 80 °C, confining pressures of 1.5–35 MPa and strain rates of ~10−5 s−1, both dry and in the presence of fluids. We determined the failure envelope, and the effect of fluids upon it, for anhydrite displaying an equigranular texture consisting of euhedral grains. We observed a general pattern of increasing peak compressive strength with increasing confining pressure, consistent with a previous study on anhydrite from the same formation, which showed an irregular texture consisting of interlocking, acicular grains embedded in a fine-grained matrix. The peak strength of euhedral anhydrite was found to be 15–65% lower than that of acicular anhydrite. No chemical effects were observed for the fluids tested. Hydraulic fracturing experiments showed the tensile strength to be approximately 4 MPa for euhedral and 6 MPa for acicular anhydrite. We combined the failure envelopes with simple, analytical calculations on the effect of cooling on in-situ stress, showing that tensile caprock failure due to cooling would be unlikely for both types of anhydrite, assuming a hypothetical reservoir at a depth of 3800 m. However, it should be noted that tensile failure may pose an issue for shallower reservoirs or weaker caprock formations.
... Because of their importance for hydrocarbon exploration , the Zechstein Carbonates have been studied by many authors, e.g. Clark (1986); van de Sande et al. (1996), who concluded that the complexity of the porosity distribution is a combination of facies and diagenesis effects. ...
For a thin reservoir, such as the Zechstein Main Dolomite (generally 33–83 m thick) of the BMB oil and gas field of Poland, where the thickness (c. 40 m) is often around a quarter of the dominant wavelength, the composite seismic response results from variations in the petrophysical properties, thickness, lithology, effective pressure and temperature, as well as in the acoustic impedance of the encasing materials. To use the BMB Field 3D seismic data for porosity prediction, 20 post-stack attributes were extracted from a seismic volume, defined by two zero-crossing time horizons that bound the reflections of the Main Dolomite. Because of the large number and the interdependency of the extracted attributes, principal component factor analysis was applied, resulting in the coding of 70% of the variability of the extracted attributes, in six orthogonal factors. Sequential nonlinear regression revealed that the first three factors, F1, F2 and F3, are the significant predictors of porosity. Cross-validation indicated a class of poorly estimated porosities resulting from poor quality/complexities in the seismic data, and a class of good porosity estimates that were subsequently used in a final cross-validation for establishing optimum weights and orders of porosity prediction polynomials. The final cross-validation indicated optimum orders of five, three and two for polynomials in F1, F2 and F3, respectively and optimum weights corresponding to validation well No. 1 (MO-3).
... For example, the main productive Zechstein horizon, the Zechstein Ze2, is prospective over a narrow east -west geographical zone. A time map can be very helpful to map the reef edge ( Van de Sande et al. 1996). ...
Fifty years after the discovery of the giant Groningen gas field, good insight into the remaining hydrocarbon exploration potential of the Netherlands is of great interest due to the aging infrastructure. In a review of prospective areas, the stratigraphic element of Dutch play areas has been summarized for conventional and unconventional formations. This is to answer the question of whether stratigraphic traps can contribute to future exploration. Complex faulting, very common in the Dutch subsurface, makes structural definition generally the highest prospect risk. With increase in 3D coverage over the country, many structures have now been drilled successfully. The success of structural traps has left the stratigraphic plays and prospects under-explored. Most hydrocarbon reserves in the Netherlands have been discovered in Permian Rotliegend and Triassic Bunter sandstone reservoirs, which are not prone to much stratigraphic trapping as a consequence of very gradual facies changes. Other prospective horizons and hydrocarbon reservoirs in the country range in age from Carboniferous to Cenozoic and can be found in clastic and carbonate rocks. They share an overall comparable basin setting but the varying interplay at basin margins creates varying stratigraphic elements. Rifting creates new facies variation during the Mesozoic. Salt movement is another factor that creates stratigraphic components in trapping. The various erosional events create other possibilities for stratigraphic trapping. This, combined with varying relative sea-levels through time, creates very distinct stratigraphic intervals often correlatable over large distances. The very limited contribution of stratigraphic traps to present-day gas finds may change in the future because of improved seismic. Risking of prospects needs better understanding of stratigraphic elements in various plays. This includes the stratigraphic aspects of reservoir sealing in dominantly structural traps and the nature of source horizons.
... One of the most widespread caprocks sealing hydrocarbon reservoirs and potential CO 2 storage sites around the world is anhydrite rock (Li et al. 2005;Chiaramonte et al. 2007;Bennion & Bachu 2008). In the Netherlands and North Sea, for example, many potential storage sites are overlain by the basal anhydrite of the Permian Zechstein evaporite sequence (Van de Sande et al. 1996; Van der Meer et al. 2006). There is accordingly much interest in quantifying damage development in anhydrite. ...
Geological storage of CO2 in depleted oil and gas reservoirs is one of the most promising options to reduce atmospheric CO2 concentrations. Of great importance to CO2 mitigation strategies is maintaining caprock integrity. Worldwide many current injection sites and potential storage sites are overlain by anhydrite-bearing seal formations. However, little is known about the magnitude of the permeability change accompanying dilatation and failure of anhydrite under reservoir conditions. To this extent, we have performed triaxial compression experiments together with argon gas permeability measurements on Zechstein anhydrite, which caps many potential CO2 storage sites in the Netherlands. Our experiments were performed at room temperature at confining pressures of 3.5–25 MPa. We observed a transition from brittle to semi-brittle behaviour over the experimental range, and peak strength could be described by a Mogi-type failure envelope. Dynamic permeability measurements showed a change from ‘impermeable’ (<10−21 m2) to permeable (10−16 to 10−19 m2) as a result of mechanical damage. The onset of measurable permeability was associated with an increase in the rate of dilatation at low pressures (3.5–5 MPa), and with the turning point from compaction to dilatation in the volumetric versus axial strain curve at higher pressures (10–25 MPa). Sample permeability was largely controlled by the permeability of the shear faults developed. Static, postfailure permeability decreased with increasing effective mean stress. Our results demonstrated that caprock integrity will not be compromised by mechanical damage and permeability development.
Geofluids (2010) 10, 369–387
The Zechstein Group in the Northern Permian Basin (UK and south Norway sectors of the North Sea) is subdivided into four halite-rich evaporitic sequences. These sequences contain K-Mg salts, the amount and distribution of which are still poorly constrained. Understanding the lithological variations of the evaporites is important for understanding the syn- to post-salt basin evolution and for predicting the development of salt caverns. We compiled well data to perform intra-salt correlations and to constrain the stratal architecture of the halite-rich units. Our results enable refinement of depositional zones of the Zechstein Group in the Northern Permian Basin with emphasis on the spatial distribution of the K-Mg salt deposits. Our analysis suggests that K-Mg salts were preferentially precipitated in the Forth Approaches Basin and north of the West Central Shelf. This was likely the result of geographic position restricting the direct influx of marine water and early halokinetic movements associated with salt relief that promoted the development of isolated intra-salt minibasins. We then use the revised stratigraphy of the Zechstein Group to propose an evolutionary scenario of the Zechstein Group that considers both the Northern Permian Basin and the Southern Permian Basin and that highlights discrepancies in the bathymetric conditions of halite deposition and the spatial repartition of the K-Mg salts. Finally, our results allow an assessment of the potential risk of finding insoluble deposits or K-Mg salts in bedded salt, salt pillows, or salt diapirs that are otherwise suitable in terms of depth and thickness for the development of salt caverns in the Northern Permian Basin.
This paper provides an updated understanding of the reservoir stratigraphy, sedimentology, palaeogeography and diagenesis of the Upper Permian Hauptdolomit Formation of the Zechstein Supergroup (“Hauptdolomit”) in a study area on the southern margin of the Mid North Sea High. The paper is based on the examination and description of core and cuttings data from 25 wells which were integrated with observations based on existing and new 3D seismic.
Based on thin-section petrography of cuttings and core from the wells studied, it is evident that Hauptdolomit microfacies are distributed in a relatively predictable way, and well-defined platform interior, platform margin, slope and basin settings can be distinguished. Platform margins are typically characterised by the development of ooid shoals and, to a lesser-extent, by microbial build-ups. High-energy back-shoal settings are characterised by a
more complex combination of peloid grainstones, thrombolitic and microbial build-ups, and fine crystalline dolomites. Lower energy lagoons which developed further behind the platform margin are characterised by a variety of microfacies types; fine crystalline dolomites are common in this setting as well as peloidal facies and local microbial build-ups. Intertidal and supratidal settings are typified by increased proportions of anhydrite and the development of laminated microbial bindstones (stromatolites). Platform margins are in general relatively steep and pass into slope and basinal settings. Only a few wells have penetrated Hauptdolomit successions deposited in a slope setting, and these successions are characterised by a range of resedimented shallow-water facies together with low-energy laminated dolomicrites and fine crystalline dolomites. Slope zones in the study area are interpreted from seismic data to be typically 1-1.5 km in width. Basinal Hauptdolomit deposits have been strongly affected by post-depositional diagenesis and are dedolomitised to variable degrees. The original depositional facies are rarely preserved.
Diagenetic studies show that dolomitisation has affected almost the entire Hauptdolomit Formation throughout the study area in both basinal and platform settings. The dolomite is considered to result from seepage-reflux processes and is an early diagenetic phase. Mouldic porosity is present in many facies types as a result of dissolution, especially in ooid grainstones, thrombolitic build-ups and peloidal facies. The dissolution cannot be associated with any one diagenetic phase but was most likely a result of the dolomitisation process itself. Stable isotope analyses indicate that all dolomites were precipitated from Permian marine derived
pore fluids. Fluid inclusion analyses of dolomite cements indicate that cementation continued into the burial realm. Anhydrite cementation occurs in two phases: early anhydrite precipitation was associated with dolomitisation, and can be distinguished from a later, pore-filling cement which is highly detrimental to
reservoir quality.
The Hauptdolomit succession in basinal wells (and in some slope wells) in the study area has undergone significant dedolomitisation. Dedolomitisation was a shallow burial process which affected precursor dolomites, whereby excess calcium from the transition of gypsum to anhydrite during burial combined with CO2 and organic acids derived from basinal sediments. The process was triggered by excess calcium reacting with excess
carbonate ions from dissolution.
3D seismic volumes supplemented by numerous 2D lines were available in the study area and allowed an interpretation to be made of Hauptdolomit gross depositional settings; platform margins and base of-slope polygons were mapped, with the greatest confidence in areas of 3D seismic. The basin, slope
and platform settings were distinguished using seismic data integrated with the results of micro-facies analysis and incorporating seismic-to-well ties. The data shows that large parts of the study area are characterised by the presence of polyhalites within the overlying (Z2) Stassfurt Halite Formation, which may create particular seismic geometries at the Hauptdolomit slope. These are interpreted to be intra-Stassfurt Halite features, providing an alternative model to the thickened,
prograded Hauptdolomit which has been suggested in previous publications.
Because few wells drilled in the study area had the Hauptdolomit as the primary target, cores were limited but significant data was obtained from cuttings analyses. More than 400 thin sections were evaluated, allowing depositional models based on microfacies observations to be developed, verifying the seismic-scale observations.
A multidisciplinary approach combining geological mapping based on seismic and well data with petrographic analyses of core and cuttings samples was used to gain a better understanding of the distribution of Upper Permian (Zechstein, Z2) Hauptdolomit platforms and their depositional facies around the Elbow Spit High in the northern Dutch offshore. A detailed understanding of the Hauptdolomit's lateral facies variability is of great importance for assessing its reservoir potential, since both the thickness and reservoir properties of these carbonate platforms greatly depend on local accommodation within different palaeo‐depositional environments. The platforms generally contain the thickest Hauptdolomit sequences and are largely characterised by a mix of oolitic and coated grainstones, as well as by some dolomicrites. Porosities of around 15% are reached at well E02‐02 within the grainstone intervals, and interconnectivity between the pores is generally present. Seismic mapping has indicated a rim of isolated Hauptdolomit platforms, which are up to 10 km wide, around the southern and NW margins of the Elbow Spit High. No Hauptdolomit platforms are present on the NE margin of the High, likely because the palaeo‐ basin margin was too steep and hence lacked accommodation for carbonate growth. Discoveries made in recent years in the UK sector of the southern North Sea have highlighted the importance of the Hauptdolomit hydrocarbon play, and the results of the current study provide a solid base for assessing the reservoir potential of this play in the relatively underexplored northern part of the Dutch offshore.
Article download: http://pgc.lyellcollection.org/content/early/2017/06/07/PGC8.9.full.pdf+html
The Mid North Sea High (MNSH) is located on the UKCS in quadrants 35–38 and 41–43. It is a large structural high that is flanked by the mature hydrocarbon provinces of the Central North Sea (CNS) to the NE and the Southern North Sea (SNS) to the SE. In the MNSH region, the source and reservoir intervals that characterize the SNS (Westphalian, Lower Permian) are absent and therefore the area is relatively underexplored compared to the SNS Basin (c. one well per 1000 km2). Nevertheless, two discoveries in Dinantian reservoirs (Breagh and Crosgan) prove that a working petroleum system is present, potentially charged either via lateral migration from the SNS or from within the lower Carboniferous itself. Additionally, gas was found in the Z2 carbonate (lower Zechstein Group) in Crosgan, with numerous other wells in the area reporting hydrocarbon shows in this unit. The results of the interpretation of recently acquired 2D and 3D seismic reflection datasets over parts of UKCS quadrants 36, 37 and 42 are presented and provide insight into both the geology and prospectivity of this frontier area.
This study suggests that intra-Zechstein clinoform foresets represent an attractive, hitherto overlooked, exploration target. The Zechstein Group sits on a major unconformity, probably reflecting Variscan-related inversion and structural uplift. Below it, fault blocks and faulted folds occur, containing pre-Westphalian Carboniferous and Devonian sediments, both of which contain potential reservoirs. In the lower Zechstein, a large build-up is observed, covering a total area of 2284 km2. This is bounded on its margins by seismically defined clinoforms, with maximum thicknesses of 0.12 s two-way time (c. 240–330 m). This rigid, near-tabular unit is clearly distinguished from the overlying deformed upper Zechstein evaporites. In map-view, a series of embayments and promontories are observed at the build-up margins. Borehole data and comparisons with nearby discoveries (e.g. Crosgan) suggest this build-up to represent a Z1–Z2 sulphate–carbonate platform, capped by a minor Z3 carbonate platform. Interpreted smaller pinnacle build-ups are observed away from the main bank. The seismic character, geometry, size and inferred composition of this newly described Zechstein platform are similar to those of platforms hosting notable hydrocarbon discoveries in other parts of the Southern Permian Basin. The closest of these discoveries to the study area is Crosgan, which is characterized by the Z2 carbonate clinothem (Hauptdolomit Formation) as a proven reservoir.
The number of papers related to rifting in the Netherlands is limited, compared to the total of papers written on the deeper subsurface and the petroleum geology of the Netherlands. It is diffuse which papers are related to the subject rifting. For example not all papers which cover inversion may have been included in the rifting category. Helpful for the comparison is an indication how many papers on other structural subjects have been written. In the graph below, the number of papers written on structural subjects in a certain year, have been compared with an estimate of the total number of papers written on subsurface subjects. Comparison of references per annum In red references related to rifting in orange related to structural subjects 0 5 10 15 20 25 30 35 40 45 50 1 Below is a listing of over 900 cited articles collected by EBN the last few years. This is by no means a complete listing. The list may be helpful for future research of the deeper subsurface. See for older reference listing, "bibliography" of Adrichem Boogaert (1987). See also for papers written on the larger North Sea area Glennie (1998) Petroleum Geology of the North Sea. Papers related to rifting in the Netherlands are estimated to amount to 40-50 or about 4% of all papers listed. There are two distinct periods such papers have been published. The first period is 1975-1985. A second period, starting in the early 1990's, peaking in 1993 and coincides with an overall increase of publications on the deep subsurface of the Netherlands over that period. Also drilling in the area was more active than presently. After 1993, the number of publications on the subject seems to level off.
A listing is provided of references relevant for the understanding of the deeper subsurface of the Netherlands, sorted by year. The list may be helpful for future research of the deeper subsurface. An alphabetical list of such references has been collected by EBN and is presented in 2006 and 2008 (van Hulten, 2006; -, 2008). Those lists have been updated and below approximately 1000 cited articles relevant for the petroleum geology of the country are given by year. The annual sorting provides an interesting insight in the development of geological thinking of the past 50 year. This year it is 50 years ago that the Permian Rotliegend play is discovered and it is now possible to see when papers on the Rotliegend appeared in the literature after the discovery. This is visualized on the graph of Fig. 1 (in blue), which shows the relative importance of the Rotliegend papers compared to the other papers dealing with other formations (in red) of the deeper subsurface. Num ber of references per annum References related to the Rotliegend (blue) It is interesting that after an initial flood of papers, starting in the late sixties, the relative importance of Rotliegend papers decreases in the eighties. There is a revival after the 1993 International AAPG conference in The Hague. That conference coincided with the success of 3D seismic as a new exploration tool. Most papers related to the deep subsurface have been written on the Rotliegend with almost 25% (see Fig. 2) of the total. About 50% of the literature is related to the period of Late Paleozoic -Early Mesozoic (Pennsylvanian part of the Carboniferous, Permian Rotliegend and Zechstein and Triassic), the period that contains the bulk of the Dutch gas reservoirs.
The shallow-marine Cretaceous Cogollo Group in the Maracaibo Basin is oil-production from fractured carbonates of low porosity and permeability. Initial production from these fields, including La Paz Field, is generally by natural flow since the Cretaceous reservoirs are highly overpressured. A study was undertaken that involved cores up to 900 feet long (275 m) from several wells, and four outcrop sections, to identify the presence of texture-related porosity and determine its origins. Two facies of the Cogollo Group exhibit such porosity: grainstone bars and pelecypod biostromes.
In 1991, the Geological Survey of the Netherlands started a project for revision and updating of the pre-Quaternary lithostratigraphy of Netherlands. This had not been done systematically since 1980. Main objective of the study are (1) to bring the lithostratigraphic ideas into agreement with new findings and increased knowledge of Dutch subsurface geology (lithostratigraphy was extended into the Lower Carboniferous and Devonian), (2) expansion and standardization of the definitions and descriptions of existing lithostratigraphic units, (3) application of modern concepts (e.g. sequence stratigraphy) in order to describe better the distribution of reservoir-prone sediments, and (4) to reach consensus on a number of stratigraphy-related subjects, such as a chronological time frame, application of biozonations, and the designation of the behavior of main structural elements through time. Eight working groups were formed, each working on a specific aspect or stratigraphic interval, under the supervision of a steering committee. Both working groups and steering committee were composed of persons from the Geological Survey, several leading oil companies and, in some cases, universities. Several working groups have completed their tasks, and updates of these stratigraphic intervals are available at the conference. Posters will display stratigraphic updates of lithostratigraphy for the Carboniferous, Zechstein, Lower Triassic,more » and Upper Jurassic-Lower Cretaceous.« less
The depositional model of the Zechstein 2 carbonate section is such a complex nature that it is not possible to predict high-porosity zones solely from geologic data. We describe a two-phase study into determination and prediction of porosities in the Zechstein 2 carbonate in the eastern Netherlands. Phase 1 was the basic feasibility study and consisted of two parts, namely, a model study followed by a well-log study. In both parts, acoustic impedance logs were filtered to test the feasibility of resolving porosity changes within the frequency range of seismic data. Phase 2 involved the prediction and verification of porosity. An exploration well, planned to penetrate the Zechstein 2 carbonate, was connected to a previously drilled carbonate test by a good quality limestone apprxoimately 60m in thickness was penetrated. From the combined well and seismic data, we predicted that a similar development of porosity could be expected in the new location. Subsequent drilling proved the presence of porous carbonate approximately 50m in thickness developed in an environment of deposition similar to that encountered in the other well. This technique has allowed us to predict reservoir porosity and will be used to develop new structural/stratigraphic prospects.- from Authors
Distribution of porosity is controlled either by a combination of depositional facies and diagenesis or by the occurrence of collapse breccias. Intragranular porosity resulting from early leaching predominates in shallow-marine grainstones and intercrystalline porosity caused by late leaching occurs in deeper-marine carbonate mudstones. Using a knowledge of facies distribution, it is possible to predict where these potential reservoirs might occur and as facies distribution can be related to the overall thickness of each carbonate unit, it is also possible to make tentative predictions of porosity distribution from isopach maps. Collapse breccias, however, are not related to any particular facies and potential reservoirs resulting from this process are most likely to be found around structural highs that became exposed at various times since the Zechstein. -from Author
Thick, shallow-water gypsum banks, formed during Zechstein times at the site of regional palaeohighs along the margins of the Southern Permian Basin, acted as foundations for shallow-water carbonate platforms. The carbonate platform margins, in particular their northern to northeastern windward margins, were characterized by deposition of grainstones dominated by aragonitic ooids, pisoids, intraclasts and bioclasts, while muddy, stromatolitic carbonates and nodular anhydrites accumulated on tidal flats and in lagoons behind the platform margins.
Usually the platforms are surrounded by thick slope deposits consisting of carbonate mudstone and redeposited intervals, but locally the platforms deepened gradually and changed, without intervening slope deposits, into a shallow-marine facies devoid of ooids. The slope aprons grade basinwards into thin successions of finely laminated carbonate.
Porosity creation in Zechstein carbonates was due to meteoric-water leaching and to subsurface leaching by carbon dioxyde-enriched formation waters during burial. Porosity destruction was mainly caused by anhydrite pore plugging and subsurface calcitization. The best reservoir properties are found in the unrestricted platform facies and in parts of the slope facies. Fractures are important in Zechstein carbonates; their presence is a prerequisite for high production rates in gasfield wells.
The distribution of porosity in Zechstein Carbonates Habitat of Palaeozoic gas in NW Europe
- D N Clark
Zechstein reservoirs in the Netherlands Classic petroleum provinces
- D Van Der Baan
1990 Geological Atlas of Western and Central Europe-Shell Internat. Petroleum Mij
- P A Ziegler