scholarly journals PETROGRAPHIC CHARACTERIZATION AND DIAGENESIS IN SANDSTONES OUTCROPS OF THE NORTHERN MACEIÓ FORMATION: IMPLICATIONS IN RESERVOIR QUALITY

2021 ◽  
Vol 15 (1-2) ◽  
pp. 37-52
Author(s):  
M. S. C. Tenório ◽  
Z. V. Batista ◽  
G. M. D. Fernandes
Keyword(s):  
Potential Method ◽  
Reservoir Quality ◽  
Petrographic Analysis ◽  
Northern Coast ◽  
Secondary Porosity ◽  
Diagenetic Processes ◽  
Geological Unit ◽  
Northern Portion ◽  
Primary Porosity

The acquisition of geological data is of fundamental importance for the study of areas potentially relevant to the occurrence of petroleum systems. In this context, the development of research in outcropping rock formations has proven to be a potential method to investigate the geology of the geological unit studied in subsurface. One of several examples found in Brazil are the outcrops Barreiras do Boqueirão and Praia de Japaratinga, belonging to the Maceió Formation, located in the northern coast of Alagoas State. The Maceió Formation has the lowest cretaceous sedimentation record within the Alagoas Basin. This sedimentation, present almost in the entire basin, is located mainly in its subsurface. This geological unit is composed of several lithologies, including a turbiditic sequence predominantly formed by shales, sandstones and conglomerates. This environment makes it possible the occurrence of a petroleum system. Our research group chose to investigate this environment because turbiditic sandstones are excellent petroleum reservoirs, and they have a great economic relevance in the Brazilian petroleum scenario. To develop this research, a petrographic characterization of the Maceió Formation sandstones was conducted to help determine the compositional and diagenetic aspects of these rocks and infer the influence of diagenetic processes on the quality of these sandstones as reservoirs. The petrographic analysis showed that the studied sandstones can be classified as arkose and quartzenite, present moderate porosity and good permeability, observed through the predominant presence of floating contacts between the grains. The porosity is predominantly primary intergranular, averaging 15%, but secondary porosity by fracture and dissolution of primary grains also occurs. The sandstones of the Maceió Formation are poorly and moderately selected, with angular, sub-angular and sub-rounded grains, showing low to medium textural maturity, which may also influence the quality of the reservoir, impairing the primary porosity in the samples. The three diagenetic stages were identified as: eodiagenesis, mesodiagenesis, and telodiagenesis. The diagenetic processes found were: mechanical compaction, beginning of chemical compaction, clay infiltration, pyrite cementation, grain dissolution, chlorite cementation, quartz sintaxial growth, and mineral alteration and replacement. Mineral replacement was a phenomenon observed quite expressively in the samples analyzed. This event was evidenced, particularly, by the substitution of muscovite and feldspar for kaolinite, the alteration of biotite was also identified in the samples. Therefore, one can infer that the diagenetic processes had little influence on the reduction of the original porosity in the samples studied. In general, considering all the analyses performed in this research, one can see that the sandstones of the Maceió Formation (northern portion) present a good reservoir quality.

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.  

Processes controlling volcanic and epiclastic reservoir formation in a buried polygenetic stratocone

2021 ◽  
pp. SP520-2021-137
Author(s):  
Alan Bischoff ◽  
Jessica Fensom ◽  
Huafeng Tang ◽  
Marcos Rossetti ◽  
Andrew Nicol
Keyword(s):  
Seismic Reflection ◽  
Geothermal Energy ◽  
Mineral Dissolution ◽  
Reservoir Quality ◽  
Petrographic Analysis ◽  
Pore Scale ◽  
Unified Framework ◽  
Mineral Alteration ◽  
Volcanic Terrains

AbstractUnderstanding the formation of volcanic and epiclastic reservoirs is pivotal for exploring geoenergy resources such as geothermal energy, hydrocarbons, and new CO2 sequestration and hydrogen storage opportunities. This paper examines the processes controlling the quality of pyroclastic and epiclastic reservoirs of the Kora volcano, an extinct stratocone presently buried in the offshore Taranaki Basin, New Zealand. We conduct detailed seismic reflection interpretation, drillcore lithofacies and wireline-log description, petrographic analysis, and analytical tests to generate a unified framework that explains the formation of volcaniclastic reservoirs from basin to pore-scale.Each stage of construction and degradation of the Kora volcano is associated with particular processes that increase or reduce reservoir quality. Primary processes include quench fragmentation, deuteric mineral dissolution, and epiclastic sedimentation. Secondary processes comprise mineral alteration (mainly meteoric; minor hydrothermal and diagenetic), mechanical stress fracturing (mainly tectonic; minor magmatic and burial deformation), and pervasive biogenic cementation. Epiclastic conglomerates present the highest reservoir quality (average 23% porosity and up to 997 mD permeability), followed by lapilli-tuffs and tuff-breccias. In contrast, bioclastic epiclastic sandstones are typically cemented by carbonates and pyrite. Our models and interpretations will increase understanding of the formation of volcaniclastic reservoirs and aid exploration of geoenergy resources in volcanic terrains.

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.

DIAGENESYS STAGE ANALYSIS OF SANDSTONE INTERVAL ON WELL DAR-24, GABUS FORMATION, ANOA FIELD, WEST NATUNA BASIN

KURVATEK ◽  
2018 ◽  
Vol 2 (2) ◽  
pp. 67-76
Author(s):  
Hanindya Ramadhani
Keyword(s):  
Secondary Porosity ◽  
Linear Distribution ◽  
Reservoir Rocks ◽  
Sandstone Diagenesis ◽  
Different Depths ◽  
Calcite Cement ◽  
Primary Porosity ◽  
Stage Analysis ◽  
Pore Lining

Stage of diagenesis of a rock will effect the quality of the rock as a reservoir. Hence, it is a necessary to analyze the diagenesis stage of sandstone at Anoa Field, West Natuna Basin, since the diagenesis stage has not been identified properly. The analysis is carried out using thin section method in five different depths. The product of diagenesis is observed for its cementation level, compaction, recrystallization, dissolution, replacement, and type of porosity wich developed in the rock. The appearance of quartz overgrowth cement and pore filling and pore lining calcite cement show a diagenesis stage which are recrystallization and cementation. The appearance of bent mica mineral and suture grain contact can be a sign of late stage compaction. Dissolution of matrix, cement and grain in the sample show that the rock has come to mesodiagenesis stage. As a result of the observation, the conclusion can be made that the rock has passed the eodiagenesis and mesodigenesis phase. Porosity of the section is both primary porosity (interparticle) and secondary porosity (dissolved) with a range 15%-20% (medium to good). Crossplot depth vs porosity show a linear distribution, which when the depth is increase the porosity will decrease. So it can be concluded that the process of diagenesis is very influential on the quality of reservoir rocks in the study area.Keyword: Gabus Formation, sandstone diagenesis, stage of diagenesis.

Diagenetic Development of Clay and Related Minerals in Deep Water Sandstones (S. Spain): Evidence of Lithological Control

Clay Minerals ◽  
1994 ◽  
Vol 29 (1) ◽  
pp. 93-104 ◽  
Author(s):  
M. D. Ruiz Cruz
Keyword(s):  
Pore Solution ◽  
Sedimentary Facies ◽  
Mineral Dissolution ◽  
Secondary Porosity ◽  
Diagenetic Processes ◽  
Reducing Conditions ◽  
Chemical Conditions ◽  
Mineral Cements ◽  
Primary Porosity ◽  
Mixed Layers

AbstractThe turbiditic facies of the Aquitanian-Oligocene of the Algeciras and Bolonia Units consist of lutitic-marly beds alternating with varied sandstones. Early diagenetic processes and the development of secondary porosity in sandstones were controlled largely by sedimentary facies. Mineral dissolution processes were important in rocks with high primary porosity (quartzose sandstones) and led to the development of allophane and kaolinite/dickite in later diagenetic stages. In rocks with high contents of biotitic matrix, chlorites and iron oxides were produced, together with the development of secondary porosity. In feldspathic sandstones, the early diagenetic processes produced chlorite, illite, illite-smectite mixed-layers and smaller amounts of kaolinite. In calcareous sandstones, the presence of an early cement prevented, to a certain extent, the dissolution of unstable fragments and restricted the development of clay minerals. The movement of fluids was not important during this early diagenetic stage in controlling the variety or abundance of mineral cements; the controlling factors were the different chemical conditions developed in the pore-solution of the various sandstone types. In spite of similar sandstone burial conditions, the different sandstone lithologies continued to determine the diagenetic processes, especially the degrees of compaction and dissolution. Certain burial processes are common to all levels: the development of reducing conditions is indicated by the development of Fe and Mn carbonates, Fe-dolomites and Fe-chlorites. A later alkaline diagenetic phase was responsible for the development of calcite, feldspar and illite. The circulation of fluids in these stages remained limited, although there was probably some movement from the lutitic-level fluids to the overlying sandstones.

scholarly journals Diagenesis and Thermal Maturity of the Cogollo Group rocks in the ANH-CR-Montecarlo-1X well, Cesar-Ranchería Basin, Colombia

2021 ◽  
Vol 48 (3) ◽  
Author(s):  
Carlos A Ríos ◽  
Mayra A Vargas ◽  
Mario García
Keyword(s):  
Organic Carbon ◽  
Total Organic Carbon ◽  
Temporal Distribution ◽  
Thermal Maturity ◽  
Secondary Porosity ◽  
Diagenetic Processes ◽  
Geological Unit ◽  
Porosity And Permeability ◽  
The Impact ◽  
Ferrous Carbonate

In ANH-CR-Montecarlo-1X well located in the southern sector of the Cesar-Ranchería basin, Colombia, rocks of the middle Cretaceous outcrop, which have been defined as belonging to the Cogollo Group. The present study concerns with the diagenetic evolution and thermal maturity of this geological unit, integrating petrographic techniques (thin section microscopy and scanning electron microscopy), geochemistry (total organic carbon and pyrolysis rock-eval) and basic petrophysics, to establish the thermal maturity and the potential of rocks as reservoirs of conventional and unconventional hydrocarbons. The results of petrographic and diagenetic analysis revealed that the rocks compositionally correspond to quartz sandstones and graywackes and carbonate rocks to mudstones and wackestones; which were affected by diagenetic processes such as compaction, mineral neoformations distinguishing minerals from the group of clays that cover the grains of the framework, and other types of precipitates of cements such as silica, ferrous and non-ferrous carbonate, some of these present partial and/or total dissolution, for which secondary porosity is recognized, also metasomatisms, where processes of chloritization and illitization of the argillaceous matrix are observed, alteration of feldspars to ferrous and non-ferrous carbonate, which affects the porosity and permeability of the rock; and recrystallization from micrite to sparite and carbonate precipitation in calcareous rocks. The study also showed that the rocks were more affected by compaction than precipitation of the different cements. The research contributes to the understanding of the impact of diagenetic processes on porosity, as well as their spatial and temporal distribution, providing diagenetic paragenesis for both siliciclastic and carbonatic rocks. When we classifying siliciclastic rocks as potential reservoir rocks, low potential results were obtained as conventional reservoirs but has good potential as non-conventional reservoirs (tight sandstones), this respect to porosity and permeability data. The geochemical studies in the calcareous rocks exhibited low to good content of total organic carbon, overmaturity state and a low generation potential with type III and IV kerogens.

scholarly journals The geology of Pegasus Basin based on outcrop correlatives in southern Wairarapa and northeastern Marlborough, New Zealand

2021 ◽  
Author(s):  
◽  
Troy Collier
Keyword(s):  
New Zealand ◽  
Seismic Interpretation ◽  
Depositional Environments ◽  
Petrographic Analysis ◽  
Contributing Factors ◽  
Secondary Porosity ◽  
Gondwana Margin ◽  
Sedimentary Fill ◽  
Primary Porosity ◽  
Clay Formation

<p>Acquisition of high quality 2D seismic data by the New Zealand Government in 2009-10 (the PEG09 Survey) sparked new interest in Pegasus Basin, an offshore frontier basin situated east of central New Zealand. Although no wells have been drilled in Pegasus Basin, strata exposed onshore in southern Wairarapa and northeastern Marlborough provide useful analogues for the sedimentary fill of the basin. Using field observations in combination with petrographic analysis and seismic interpretation, this study provides a more complete understanding of the geology of Pegasus Basin.  13 outcrop localities are described from the surrounding southern Wairarapa and northern Marlborough regions, which are inferred to have been deposited in a range of depositional environments including fluvial, terrestrial and shallow marine deposits, through to inner – mid shelf, and deep marine channel-levee and submarine fans, with fine-grained sedimentation at bathyal depths. These outcrops provide representative and well-exposed examples of facies and lithologies typical of the depositional environments that are likely to exist in Pegasus Basin.  Petrographic analysis of six Cretaceous and six Neogene sandstones from Marlborough and Wairarapa regions has revealed that they are compositionally classified as litharenites and feldspathic litharenites, derived from the Torlesse Supergroup. Primary porosity is best preserved in Neogene sandstones, whilst Cretaceous sandstones only tend to preserve secondary porosity, in the form of fractures or dissolution of framework grains. Carbonate cementation, compaction and authigenic clay formation are the biggest contributing factors that degrade reservoir quality.  Seismic interpretation of the PEG09 survey has revealed that Pegasus Basin contains a sedimentary succession over 10,000 m thick, that mantles Early Cretaceous syn-tectonic strata in various states of deformation attained during mid-Cretaceous subduction at the eastern Gondwana margin. Key horizons mapped extensively over the basin highlight seismic reflection packages, which are linked to described outcrop localities onshore, based on reflection characteristics and geometries. The Miocene succession contains up to 4,000 m of sediments that are likely to include promising reservoir lithologies akin to the Great Marlborough Conglomerate of Marlborough, or the Whakataki Formation of Wairarapa.</p>

GEOLOGICAL CONTROLS ON RESERVOIR QUALITY OF THE NORTHERN PERTH BASIN

1987 ◽  
Vol 27 (1) ◽  
pp. 318 ◽  
Author(s):  
S.L. Bergmark ◽  
P.R Evans
Keyword(s):  
High Energy ◽  
Reservoir Quality ◽  
Gas Field ◽  
Reservoir Rocks ◽  
The North ◽  
Fan Delta ◽  
The Common ◽  
Primary Porosity ◽  
And Control

The major onshore Dongara gas field and a number of adjacent minor gas and oil pools are reservoired in basal Triassic sandstones that are sealed by the overlying Kockatea Shale. Reservoir quality is found to be controlled primarily by the local provenance of the sandstones, by diagenesis and the regional palaeotopography. Sandstones east of Dongara are reworked products of a Late Permian fan delta (Wagina Sandstone) that extended westwards from the basin's eastern, fault controlled margin. Localised high energy streams drained the palaeoslope, depositing thin wedges of mainly fluvial sediments upon and around the flanks of the Permian fan delta during a regional rise in sea level in the Early Triassic. Sandstones to the north of Dongara are localised, low energy offshore bars and strandline deposits derived from Precambrian of the Northampton Block. Diagenetic alterations of the Triassic sandstones, also controlled by the sandstones' provenance, have substantially reduced primary porosity and control permeability. The common presence of the authigenic clay mineral, dickite, is taken as evidence that a fluvial environment of deposition controlled formation of the reservoir rocks.

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 Diagenetic controls on reservoir quality of tight sandstone: A case study of the Upper Triassic Yanchang formation Chang 7 sandstones, Ordos Basin, China

2018 ◽  
Vol 22 (2) ◽  
pp. 129-138 ◽  
Author(s):  
Haihua Zhu ◽  
Guangchen Liu ◽  
Dakang Zhong ◽  
Tingshan Zhang ◽  
Jun Lang ◽  
...  
Keyword(s):  
Late Stage ◽  
Ordos Basin ◽  
Mineral Dissolution ◽  
Reservoir Quality ◽  
Tight Sandstone ◽  
Pore Characteristics ◽  
Mechanical Compaction ◽  
Primary Porosity ◽  
The Impact

Through a range of petrological techniques, the petrology, diagenesis, pore characteristics, and controlling factors on the regional variations of reservoir quality of the Chang 7 sandstones were studied. These sandstones, mainly arkoses, lithic arkoses, and feldspathic litharenites, were deposited in a delta front and turbidites in semi-deep to deep lacustrine. The detrital constituents were controlled by the provenance and sedimentary condition, which resulted in a spatially variable composition; e.g., high biotite and feldspar contents in the northeast (NE) of the study area, and high contents of rock fragments, especially dolomite, matrix, and quartz in the southwest (SW). Diagenesis includes intense mechanical compaction, cementation, and dissolution of unstable minerals. Diagenetic minerals which were derived internally include quartz, ankerite, ferrous calcite, albite, illite, kaolinite, and chlorite. Thus the original sandstone composition hadfirm control over the development and distribution of cement. Mechanical compaction and late-stage cementations contribute to the porosity loss of sandstones of Chang7 member. The dissolution porosity in major sandstone, slightly higher than primary porosity is principally dependent on the accessibility of acid fluid. The high content of plastic component facilitated the reduction of primary porosity and limited the mineral dissolution. The best reservoir sandstones are found in W, and partly from NE, M districts, with porosity are primary. The relatively high textural maturity of these sandstones reduces the impact of compaction on primary pores, and commonly existed chlorite rims limited the precipitation of pore filling quartz and carbonate cementation in late stage.

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