FAULT-RELATED CALCITE CEMENTATION: IMPLICATIONS FOR TIMING OF HYDROCARBON GENERATION AND MIGRATION AND SECONDARY POROSITY DEVELOPMENT, BARROW SUB BASIN, NORTHWEST SHELF

2000 ◽  
Vol 40 (1) ◽  
pp. 213
Author(s):  
G.M. Kraishan ◽  
N.M. Lemon
Keyword(s):  
Carbon Isotopic Composition ◽  
Reservoir Quality ◽  
Hydrocarbon Generation ◽  
Pore Waters ◽  
Secondary Porosity ◽  
North West ◽  
Carbon Isotopic ◽  
Authigenic Mineral ◽  
And Migration ◽  
Primary Porosity

Calcite is a common authigenic mineral in subsurface sandstones of the Barrow Sub-basin, North West Shelf. It is present in several formations from different stratigraphic horizons, ranging from Permian to Cretaceous. It occurs as poikilotopic cement and fracture-fill particularly concentrated along one of the major listric faults in the eastern part of the sub-basin. A detailed petrographical and geochemical study was performed on the Early Cretaceous calcite cements in an attempt to provide information on their origin, distribution and effect on reservoir quality. Calcite cements are Ca-rich, Mg-poor with considerable amounts of Fe and are characterised by bright orange to yellow luminescent colours. The δ13C and δ180 values vary considerably, δ13C ranging from −2.0 to −23.5 %o PDB (average of −10.2 %o, ± 4.8 PDB), whilst δ180 values range from 19.3 to 25.4 SMOW (average of 21.1 %o, ± 1.8 SMOW). Calcite cements are characterised by elevated 87Sr/86Sr ratios with a range of 0.71029 to 0.71058 (average of 0.71043 ± 0.00012). The elemental and stable isotope compositions of the calcite cements indicate cementation from meteoric pore-waters, with the same source and timing of occurrence.Calcite cements formed in the mid-diagenetic history below 45°C. The carbon isotopic composition of calcite cements is interpreted to be sourced from bicarbonate and carbon dioxide generated by thermal decarboxylation of kerogen and oxidation of the early-generated oil. The model for calcite formation involves fluids rich in organic carbon having migrated up dip along faults to be trapped and mixed with meteoric-derived C02 to form pervasive calcite-cemented zones. These zones may reach up to 8 m thick and occlude the intergranular primary porosity. Subsequent tectonic reactivation and maturation of organic matter has resulted in late acidic water invasion to partially or completely dissolve the calcite cement to locally enhance reservoir quality.

UPPER PERMIAN CARBONATE RESERVOIRS OF THE NORTH WEST SHELF AND NORTHERN PERTH BASIN, AUSTRALIA

1999 ◽  
Vol 39 (1) ◽  
pp. 343 ◽  
Author(s):  
J.D. Gorter ◽  
J.M. Davies
Keyword(s):  
Oil And Gas ◽  
Upper Permian ◽  
Gas Reservoirs ◽  
Secondary Porosity ◽  
North West ◽  
Associated Gas ◽  
The North ◽  
Timor Sea ◽  
Primary Porosity ◽  
Carnarvon Basin

The Perth, Carnarvon, Browse, and Bonaparte basins contain Permian shallowmarine carbonates. Interbedded with clastic oil and gas reservoirs in the northern Perth Basin (Wagina Formation), and gas reservoirs in the Bonaparte Basin (Cape Hay and Tern formations), these carbonates also have the potential to contain significant hydrocarbon reservoirs. Limestone porosity may be related to the primary depositional fabric, or secondary processes such as dolomitisation, karstification, and fracturing. However, in the Upper Permian interval of the North West Shelf and northern Perth Basin, where there are no indications of significant preserved primary porosity in the limestones, all known permeable zones are associated with secondary porosity. Fractured Permian carbonates have the greatest reservoir potential in the Timor Sea. Tests of fractured Pearce Formation limestones in Kelp Deep–1 produced significant quantities of gas, and a test of fractured Dombey Formation limestone in Osprey–1 flowed significant quantities of water and associated gas. Minor fracture porosity was associated with gas shows in dolomitic limestones in Fennel–1 in the Carnarvon Basin, and fractures enhance the reservoir in the Woodada Field in the northern Perth Basin. Karst formation at sub-aerial unconformities can lead to the development of secondary porosity and caverns, as in the Carnarvon Basin around Dillson–1. Minor karst is also developed at the top Dombey Formation unconformity surface in the Timor Sea region.

Diagenetic Control of Porosity and Permeability in Pakawau and Kapuni Group Sandstones, Taranaki Basin, New Zealand

1988 ◽  
Vol 6 (3) ◽  
pp. 263-280 ◽  
Author(s):  
J.D. Collen
Keyword(s):  
New Zealand ◽  
Hydrocarbon Generation ◽  
Burial Diagenesis ◽  
Secondary Porosity ◽  
Calcite Dissolution ◽  
Reservoir Rocks ◽  
Porosity And Permeability ◽  
Reservoir Porosity ◽  
Primary Porosity ◽  
Depth Of Burial

Porosity and permeability of Cretaceous to Oliogocene Pakawau and Kapuni Group sandstones in Taranaki Basin, New Zealand, have been extensively modified by burial diagenesis. Mechanical compaction and the precipitation of silica, carbonate and authigenic clays have caused marked deterioration of potential and actual reservoirs for hydrocarbons. Other authigenic minerals have had less effect. Secondary reservoir porosity and permeability have developed in significant volumes in sandstones at various places, at depths below about 2.5 km. They have formed by dissolution of detrital grains, authigenic cements and authigenic replacement minerals, and by fracturing of rock and grains. The most important process for commercial hydrocarbon accumulation in New Zealand is mesogenetic carbonate (particularly calcite) dissolution. As the most prospective source and reservoir rocks are low in the Cretaceous-Tertiary sequence, the depth of burial necessary for hydrocarbon generation means that most primary porosity has been lost and secondary porosity is essential for a commercial accumulation. Entrapment of hydrocarbons in reservoirs higher in the sequence probably also requires the development of secondary permeability to allow migration.

scholarly journals Diagenesis and reservoir quality evolution of the paleogene sokor1 sandstones in the agadem block, termit basin, eastern Niger

2019 ◽  
Vol 7 (2) ◽  
pp. 147
Author(s):  
HAMMA ADA Moussa ◽  
MOUSSA Harouna
Keyword(s):  
Reservoir Quality ◽  
Petrographic Analysis ◽  
Secondary Porosity ◽  
Oil Accumulation ◽  
Average Mass ◽  
Rock Fragments ◽  
Hydrocarbon Reservoir ◽  
Quartz Arenite ◽  
Primary Porosity ◽  
Diagenetic History

The Paleogene Sokor1 Formation in Termit Basin is recognized as the most important hydrocarbon reservoir. However, in spite of its reservoir importance, published studies on its diagenetic process and their effects on reservoir quality are absent or limited. Petrographic analysis, scanning electron microscopy and X-ray diffraction were used to assess diagenetic characteristics, controls on reservoir and reservoir quality of Sokor1 Formation. The Sokor1 sandstones are mostly quartz sandstone, lithic quartz-arenite and rarely lithic fedspathic-quartz-arenite, with an average mass fraction of quartz 95%, feldspar 1.6% and rock fragments 3.4% (Q95F1.6R3.4). Diagenetic processes in Sokor1 sandstones include mechanical compaction, cementation, dissolution and replacement. The main authigenic minerals are quartz overgrowth and clay minerals, which occur as pore-filling and pore-lining cements. Sokor1 sandstone has undergone stages A and B of eodiagenesis and now, it is experiencing stage A of mesodiagenesis. The widespread occurrences of quartz overgrowth suggest that Sokor1 sandstones lost a significant amount of primary porosity during its diagenetic history. Secondary porosity occurred due to partial and complete dissolution of feldspar, quartz grains and rock fragments, so increasing reservoir quality. The latter is predominantly controlled by depositional environment controls on grains size, sorting and matrix. Thus, reservoirs of best quality were deposited in braided river channel environments. In addition, oil accumulation has no discernable effects on porosity and oil probably entered the reservoir at late diagenetic stage, after quartz overgrowth and authigenic cements had already occurred.  

DEPOSITION AL AND DIAGENETIC CONTROLS ON THE QUALITY OF BARROW GROUP SANDSTONE RESERVOIRS, BARROW SUB-BASIN, NORTH WEST SHELF, WESTERN AUSTRALIA

1997 ◽  
Vol 37 (1) ◽  
pp. 214 ◽  
Author(s):  
G. M. Kraishan ◽  
N. M. Lemon ◽  
P.R. Tingate
Keyword(s):  
Grain Size ◽  
Fine Sand ◽  
Potassium Feldspar ◽  
Coarse Grained ◽  
Reservoir Quality ◽  
Secondary Porosity ◽  
Intergranular Porosity ◽  
North West ◽  
Mechanical Compaction

The main controls on Barrow Group reservoir quality are depositional (lithofacies) and post depositional (di- agenetic). Barrow Group sediments were deposited in environments ranging from non-marine to deep marine. The upper sandstones (Flacourt Formation) in the centra] and southern parts of the sub-basin are dominantly of good reservoir quality, consisting mainly of marine- reworked strandplain and shoreface deposits. The lower sandstones (Malouet Formation), however, in the Barrow Sub-basin depocentre, are composed predominantly of slope apron deposits, consisting of tight, matrix-rich, non-productive sandstones. The Flag Sandstone, distributed along the northern part of the sub-basin, is made up mainly of mounded turbidite deposits consisting of excellent reservoir quality, coarse-grained sheet turbid-ites.Petrographic observations of theliarrow Group show that sands are, in general, extremely well sorted and display a unimodal grain-size distribution. Grain size varies slightly with the depositional environment; the mounded turbidite sandstones average 197 f.im (fine sand) and the slope apron sandstones average 185 pm (fine sand). The grain size in the marine-reworked strandplain sandstones averages 300 j.im (medium sandstones). Detrital depositional matrix, mechanical compaction and cementation are the main causes of poor reservoir quality. Mechanical compaction is responsible for destroying up to 60 per cent of the original porosity. Chemical compaction has had much less effect. Precipitation of authigenic minerals has reduced, on average, the primary intergranular porosity to 12 per cent of the whole rock-volume.In some cases, secondary porosity development has greatly enhanced the reservoir quality of the Barrow Sub-basin sandstones. It results from dissolution of calcite, dolomite and potassium feldspar. Reservoir quality is most improved along the margins of the sub-basin as this is where carbonate and feldspar were most abundant.

scholarly journals Thermo-Physical and Geo-Mechanical Characterization of Faulted Carbonate Rock Masses (Valdieri, Italy)

2019 ◽  
Vol 11 (2) ◽  
pp. 179 ◽  
Author(s):  
Jessica Chicco ◽  
Damiano Vacha ◽  
Giuseppe Mandrone
Keyword(s):  
Heat Transfer ◽  
Thermal Conductivity ◽  
Rock Mass ◽  
Thermal Response ◽  
Rock Masses ◽  
Secondary Porosity ◽  
Rock Interaction ◽  
North West ◽  
Key Factor ◽  
Primary Porosity

Water in rock masses is a key factor in geo-mechanics, hydrogeology, mining, geo-thermics, and more. It is relevant in interpreting rock mass behavior (e.g., water-rock interaction or slope stability), as well as in defining heat transfer mechanisms. Pointing out the contribution of secondary porosity in increasing advective heat transfer instead of the conduction phenomenon, this study aims to highlight a different thermal response of sound rocks and faulted zones. Moreover, it provides some methodological suggestions to minimize environment disturbance in data collection and a robust interpretation of the results. An interesting outcrop was identified in a carbonate quarry near Valdieri (north-west Italian Alps): it was studied coupling a geo-mechanical and a thermo-physical approach. In particular, geo-mechanical and photogrammetric surveys, InfraRed Thermography (IRT), and Thermal Conductivity (TC) measurements were conducted. The rationale of the research is based on the fact that, when a substantial temperature difference between flowing groundwater and rocks was detected, IRT can reveal information about geo-mechanical and hydrogeological properties of the rock masses such as a degree of fracturing and joint interconnection. A comparative field and laboratory analysis using different devices enabled a more detailed insight providing values in both dry and wet conditions. A different thermal response was highlighted for the cataclastic zone as well. IRT results showed an evident inverse relationship among the number of joints per meter and the detected surface temperature. This is probably caused by the higher water flow within the cataclastic fault zone. Moreover, low fractured portions of the rock mass presented higher cooling rates and conducted heat far more than those with poor geo-mechanical characteristics (difference up to 40%). A negligible ratio between wet and dried thermal conductivity (about 1%) was also detected in lab measurements, which confirmed that primary porosity is not usually relevant in influencing thermal properties of the sound rock.

Evolution of Radiocarbon in a Sandy Aquifer Across Large Temporal and Spatial Scales: Case Study from Southern Poland

Radiocarbon ◽  
2013 ◽  
Vol 55 (2) ◽  
pp. 905-919 ◽  
Author(s):  
M Dulinski ◽  
K Rozanski ◽  
T Kuc ◽  
Z Gorczyca ◽  
J Kania ◽  
...  
Keyword(s):  
Isotopic Composition ◽  
Unsaturated Zone ◽  
Dissolved Inorganic Carbon ◽  
Geochemical Modeling ◽  
Spatial Scales ◽  
Carbon Isotopic Composition ◽  
Pore Waters ◽  
Southern Poland ◽  
Carbon Isotopic ◽  
Sandy Aquifer

We present the results of a comprehensive study aimed at tracing the evolution of carbon isotopic composition of the TDIC (total dissolved inorganic carbon) reservoir from the unsaturated zone down to the discharge area, in a sandy aquifer near Kraków, southern Poland. A multilevel well penetrating the unsaturated zone in the study area was equipped with horizontally mounted lysimeters with ceramic suction cups to collect samples of pore water and metal probes to collect soil air. Strong seasonal fluctuations were observed of soil pCO2 extending down to the water table, coupled with distinct, well-defined depth profiles of δ13CTDIC reaching approximately −10′ at 8 m depth and almost constant radiocarbon content in the TDIC pool, comparable to 14CO2 levels in the local atmosphere. Simple models (closed/open system) do not account for the observed depth variations of carbon isotopic composition of the TDIC pool. This suggests that the TDIC reservoir of pore waters is evolving under conditions gradually changing from an open towards a closed system. In order to explain 13C and 14C content of dissolved carbonates in groundwater in the recharge area of the studied aquifer, additional sources of carbon in the system are considered, such as organic matter decomposition accompanied by reduction of dissolved nitrates and sulfates. The piston-flow l4C ages of groundwater in the confined part of the studied system were calculated using 2 approaches: 1) the correction model proposed by Fontes and Garnier (1979) was used to calculate groundwater ages, utilizing the chemical and carbon isotopic data available for the sampled wells; and 2) inverse geochemical modeling was performed for selected pairs of wells using NETHPATH code. The calculated 14C ages of groundwater range from approximately 0.6 to 37.5 ka BP. Although both methods appeared to be in a broad agreement, NETHPATH calculations revealed that isotopic exchange processes between TDIC pool and solid carbonates present in relatively small amounts in the aquifer matrix play an important role in controlling the 13C and 14C signatures of the dissolved carbonate species in groundwater and should be taken into account when 14C ages are calculated.

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