Carbonate Diagenesis in a Sequence Stratigraphic Framework; Case study from Miocene Dam Formation, Eastern Saudi Arabia

2020 ◽  
Author(s):  
Moaz Salih ◽  
Osman Abdullatif ◽  
Khalid Al-Ramadan ◽  
Mazin Bashri
Keyword(s):  
Saudi Arabia ◽  
Arabian Plate ◽  
Sequence Stratigraphic ◽  
Hydrocarbon Reservoir ◽  
Diagenetic Processes ◽  
Porosity And Permeability ◽  
Thin Section Petrography ◽  
Calcite Cement ◽  
Sequence Boundaries ◽  
Analytical Tools

<p>The Miocene Dam Formation in the Al-Lidam area of Eastern Saudi Arabia consists of a succession </p><p>of mixed siliciclastic-carbonate sequences that were deposited during Miocene (Burdigalian) </p><p>times. Stratigraphic equivalents of the Dam Formation occur as hydrocarbon reservoir intervals in </p><p>the Arabian Plate. Reservoir quality of carbonate rocks is controlled by a combination of </p><p>depositional setting and post-depositional diagenetic factors. </p><p>In this study, fifteen lithofacies were identified as they were deposited on a low angle dipping </p><p>carbonate ramp, under supratidal, beach, intertidal and shallow subtidal conditions. Carbonate </p><p>diagenesis has been examined using: thin-section petrography, SEM, XRD and </p><p>cathodoluminescence. These analytical tools have shown that the intertidal lithofacies are </p><p>influenced by extensive meteoric dissolution and minor cementation. Marine diagenesis was </p><p>restricted to beach grainstone and subtidal lithofacies, in the form of aragonite and high magnesium </p><p>calcite cement. Shallow burial conditions were inferred by grain contacts represented by point, </p><p>suture and concavo-convex contacts. Mimetic dolomitization for the whole succession was also </p><p>observed. Three fourth - order, shallowing upward sequences were identified in the study area, and </p><p>they are separated by two sequence boundaries. A clear relation between sequence surfaces and </p><p>diagenetic processes was observed; meteoric diagenesis and dolomitization increases upwards in </p><p>each sequence. Porosity and permeability measurements have shown that the highest values are </p><p>associated with the HST of each sequence, followed by the TST and the LST. The results of this </p><p>study can help in understanding of diagenetic processes, and consequently in developing better </p><p>and more accurate predictions of the porosity and permeability distribution within hydrocarbon </p><p>reservoirs.</p><p> </p>

The complexity of carbonate porosity distribution in the Upper Marrat Formation, Central Saudi Arabia

2020 ◽  
Author(s):  
Saleh Ahmed ◽  
Luis González ◽  
Johannes Jozef Gerardus Reijmer ◽  
Ammar ElHusseiny
Keyword(s):  
Saudi Arabia ◽  
Carbonate Rocks ◽  
Early Jurassic ◽  
Arabian Plate ◽  
Permeability Evolution ◽  
Depositional Processes ◽  
Bedding Planes ◽  
Tectonic Processes ◽  
Porosity And Permeability ◽  
The Impact

<p>In terms of reservoir properties distribution carbonate rocks are very heterogeneous. Moreover, the types of porosity in carbonate rocks is very diverse. In our study of the Upper Marrat Formation near Khasm-adh-Dhibi (central Saudi Arabia) we have documented the pore system complexity and are deconvolving the impact of various post-depositional processes on porosity and permeability evolution of the formation. The Upper Marrat Formation is exposed in the central part of the Arabian plate in a north-south elongated mountain belt. It forms the lower part of the thick Jurassic petroleum-rich succession. The sediments forming the Upper Marrat Formation were deposited during the Early Jurassic time, the Toarcian. The Upper Marrat Formation shows fossiliferous biomicrite to sparse biomicrite carbonates with an evaporite deposit at the top. It is bounded by clayey units at both the top and the base. In general, because of the muddy matrix of the Upper Marrat, sediments are very tight and show low permeability. During the last 175 My, the Upper Marrat has been subjected to a series of diagenetic and tectonic processes. The initial micro- and intergranular porosity was reduced due to early compaction and cementation, however, during later diagenesis and tectonism, porosity and permeability were enhanced. The dominant diagenetic porosity in the Upper Marrat sediments is vuggy porosity, followed by fabric selective intragranular porosity. Many of the horizons in the Upper Marrat are heavily burrowed and mostly filled with sand-sized grains showing a higher porosity than the matrix. Dolomite is limited to evaporite strata and contain extensive inter-crystalline porosity produced during dolomite formation. Tectonism has enhanced porosity through the development of micro- and macro-fractures.  The different sized and orientated micro-fractures are important while they enhance permeability by connecting different pore types. Then extensive macro-fracture network has a major impact on the reservoir qualities, both porosity and permeability. The heavily fractured formation shows numerous fractures sets with NNE to SSW and ENE to WNW orientations. Fractures are mostly vertical to near-vertical; they are nearly all open, and often crosscut beds, or end at bedding planes. These fractures are the most abundant porosity type and their connectivity results in a very high permeability. In conclusion, initial porosity and permeability, and subsequent diagenetic and tectonic processes reduced and enhanced the porosity and permeability development of the sediments of the Early Jurassic Upper Marrat Formation.</p>

scholarly journals Sedimentological characterization of the mid-Cretaceous Mishrif reservoir in southern Mesopotamian Basin, Iraq

GeoArabia ◽  
2013 ◽  
Vol 18 (1) ◽  
pp. 139-174
Author(s):  
Thamer A. Mahdi ◽  
Adnan A.M. Aqrawi ◽  
Andrew D. Horbury ◽  
Govand H. Sherwani
Keyword(s):  
United Arab Emirates ◽  
Effective Porosity ◽  
Arabian Plate ◽  
Primary Control ◽  
Sea Level Changes ◽  
Sequence Stratigraphic ◽  
Oil Reserves ◽  
Pattern Sequence ◽  
Sequence Boundaries ◽  
Local Tectonics

ABSTRACT The CenomanianÐEarly Turonian reservoirs of the Mishrif Formation of the Mesopotamian Basin hold more than one-third of the proven Iraqi oil reserves. Difficulty in predicting the presence of these mostly rudistic reservoir units is mainly due to the complex paleogeography of the Mishrif depositional basin, which has not been helped by numerous previous studies using differing facies schemes over local areas. Here we present a regional microfacies-based study that incorporates earlier data into a comprehensive facies model. This shows that extensive accumulation of rudist banks usually occurred along an exterior shelf margin of the basin along an axis that runs from Hamrin to Badra and southeast of that, with additional interior rudist margins around an intra-shelf basin to the southwest. Regional tectonism defined the accommodation sites during the platform development. Facies analysis allowed the recognition of 21 microfacies types and their transgressive-regressive cyclic stacking pattern. Sequence-stratigraphic analysis led to the recognition of three complete third-order sequences within the studied Mishrif succession. Eustatic sea-level changes were the primary control on this sequence development but local tectonics was important at the Cenomanian/Turonian boundary. Rudist biostromes are stacked as thicker shallowing-up cycles composed of several smaller-scale cycles. In places, smaller cycles are clearly shingled (stacked laterally). Iraq’s Mishrif sequences are thus analogous to coeval systems across the Arabian Plate in Oman, United Arab Emirates, offshore Saudi Arabia and Kuwait, southwest Iran and the Levant. Analysis of poroperm trends shows porosity increasing beneath sequence boundaries due to karstification and meteoric dissolution. The presence of interconnected vugs in grain-dominated fabric make the rudist biostromes the best reservoir units. Dissolution of aragonitic components of rudist shells was the most important diagenetic process that enhanced reservoir characteristics. The presence of rudist-bearing facies with their diagenetic overprint within regressive cycles is considered the primary factor in effective porosity development and distribution. As a result, because of depositional heterogeneities (facies type distribution and their 3-D geometries) and the influence of sequence boundaries on reservoir quality, each field shows unique geometrical combinations of pay zones, barriers and seals.

scholarly journals Coupled experimental/numerical workflow for assessing quantitative diagenesis and dynamic porosity/permeability evolution in calcite-cemented sandstone reservoir rocks

2018 ◽  
Vol 73 ◽  
pp. 36 ◽  
Author(s):  
Steven Claes ◽  
Fadi H. Nader ◽  
Souhail Youssef
Keyword(s):  
Permeability Evolution ◽  
Flow Properties ◽  
New Approach ◽  
Reservoir Rocks ◽  
Pore Blocking ◽  
Diagenetic Processes ◽  
Porosity And Permeability ◽  
Sandstone Reservoir ◽  
Calcite Cement ◽  
Host Rocks

Some of the world best hydrocarbon reservoirs (carbonates and siliciclastics) are also believed to be valuable for subsurface storage of CO2 and other fluids. Yet, these reservoirs are heterogeneous in terms of their mineralogy and flow properties, at varying spatial-temporal scales. Therefore, predicting the porosity and permeability (flow properties) evolution of carbonates and sandstones remains a tedious task. Diagenesis refers to the alteration of sedimentary rocks through geologic time, mainly due to rock-fluid interactions. It affects primarily the flow properties (porosity and permeability) of already heterogeneous reservoir rocks. In this project a new approach is proposed to calculate/quantify the influence of diagenetic phases (e.g. dissolution, cement plugging) on flow properties of typical sandstone reservoir rocks (Early Jurassic Luxembourg Formation). A series of laboratory experiments are performed in which diagenetic phases (e.g. pore blocking calcite cement in sandstone) are selectively leached from pre-studied samples, with the quantification of the petrophysical characteristics with and without cement to especially infer permeability evolution. Poorly and heavily calcite-cemented sandstone samples, as well as some intermediate cemented samples were used. The results show a distinctive dissolution pattern for different cementation grades and varying Representative Elementary Volumes (REVs). These conclusions have important consequences for upscaling diagenesis effects on reservoirs, and the interpretation of geochemical modelling results of diagenetic processes. The same approach can be applied on other type of cements and host-rocks, and could be improved by integrating other petrophysical analyses (e.g. petroacoustic, NMR).

scholarly journals Significant new biostratigraphic horizons in the Qusaiba Member of the Silurian Qalibah Formation of central Saudi Arabia, and their sedimentologic expression in a sequence stratigraphic context

GeoArabia ◽  
2005 ◽  
Vol 10 (1) ◽  
pp. 49-92 ◽  
Author(s):  
A. Miller Merrell ◽  
Melvin John
Keyword(s):  
Saudi Arabia ◽  
Sea Level ◽  
Arabian Plate ◽  
Important Species ◽  
Sequence Stratigraphic ◽  
Facies Associations ◽  
Global Sea Level ◽  
High Level ◽  
A Minor ◽  
Stratigraphic Evolution

ABSTRACT Detailed analysis of over 1,000 subsurface Silurian palynology samples from 34 wells has allowed the development of a robust biostratigraphy based on acritarchs, chitinozoans and cryptospores for the Qusaiba Member of the Qalibah Formation, central Saudi Arabia. The new index fossils described herein augment the Arabian Plate Silurian chitinozoan zonation. The high-resolution biostratigraphic zonation consists of nine First Downhole Occurrences (FDOs) from the lower Telychian through Aeronian. In particular, three regionally recognizable palynologic horizons were identified within the lower part of the informally designated Mid-Qusaiba Sandstone (Angochitina hemeri Interval Zone), and above the FDO of Sphaerochitina solutidina. This high level of biostratigraphic resolution provides a framework for the integration of the sedimentology and calibration with global sea level curves, leading to a detailed understanding of the sequence stratigraphic evolution of this part of the Silurian in Saudi Arabia. Sedimentological core studies identify three Depositional Facies Associations (DFAs) within the Mid-Qusaiba Sandstone interval, including: (1) shelfal deposits (DFA-I) characterized by interbedded hummocky cross-stratified sandstones, graded siltstones and bioturbated mudstones; (2) turbiditic deposits (DFA-II); and (3) an association of heavily contorted and re-sedimented sandstones, siltstones and mudstones (DFA-III) that is considered representative of oversteepened slopes upon the Qusaiba shelf. Integration of the newly recognized palynostratigraphic horizons and the sedimentological data facilitates an understanding of the sequence stratigraphic evolution of the Mid-Qusaiba Sandstone interval and its immediate precursors. Thus a Maximum Flooding Surface (MFS) is identified from significant palynostratigraphic, as well as sedimentological evidence, and concurs with the MFS identified regionally with the Monograptus convolutus Graptolite Zone. Several mud-prone cyclothems downlap onto the MFS. Each of these is identified by its own palynostratigraphic marker: these mud-prone cyclothems represent the distal parts of a Highstand Systems Tract (HST). The end of the HST is marked by evidence of a major, episodic drop in relative sea level. Thus, a relationship is identified wherein successive palynostratigraphic marker horizons, newly identified in this study, are partially eroded by the introduction of sandy turbidites (DFA-II). These turbidites arise from storm-induced erosion of gully complexes in the upper submarine slopes that are present as topography upon the Qusaiba shelf. Each of the successive drops in sea level is separated from the next by a minor, subsequent sea level rise, which precludes further submarine erosion and turbidite deposition, and is instead evident in the widespread occurrence of shallow marine (shelfal) muds and sandy tempestites (DFA-I). The lowstand per se is considered to be represented by the most widespread distribution of the DFA-II turbidite deposits, and is associated with the youngest Mid-Qusaiba Sandstone marker horizon identified in this study, namely Rugosphaera agglomerata n.sp. The youngest unit of DFA-II lowstand turbidites is limited in its occurrence to the more proximal parts of the study area, and thus is considered to represent the onset of the succeeding Transgressive Systems Tract (TST). Of the biostratigraphic indices used for correlation within the Qusaiba Member, Rugosphaera agglomerata and Eupoikilofusa curvata are formally described and two additional important species, Fractoricoronula n.sp. and ?Oppilatala n.sp., are retained in open nomenclature.

scholarly journals Insight into Heterogeneous Calcite Cementation of Turbidite Channel-Fills from UAV Photogrammetry

Geosciences ◽  
2019 ◽  
Vol 9 (5) ◽  
pp. 236 ◽  
Author(s):  
Mattia Marini ◽  
Giovanna Della Porta ◽  
Fabrizio Felletti ◽  
Benedetta Marcella Grasso ◽  
Marica Franzini ◽  
...  
Keyword(s):  
Spatial Distribution ◽  
Volume Fraction ◽  
Pore Space ◽  
Burial Depth ◽  
Channel Axis ◽  
Reservoir Properties ◽  
Hydrocarbon Reservoir ◽  
Cumulative Volume ◽  
Porosity And Permeability ◽  
Calcite Cement

Diagenesis is a key controlling factor on sandstone porosity and permeability. Understanding type, paragenetic sequence and spatial patterns of cements is thus important for assessing sandstone hydrocarbon reservoir properties. In this study Unmanned Aerial Vehicle (UAV) photogrammetry is used to evaluate the shape and spatial distribution of calcite concretions developed within the sand-prone fill of a turbidite channel. The studied channel-fill is entrenched into hemipelagic marlstones and include a lower conglomeratic sandstone loaded with marlstone rip-ups and an upper fill featuring a range of turbidite bed types, which, up-section and off the channel axis, are progressively finer grained and less amalgamated. Concretion shape analysis highlighted a continuum of equant to oblate shapes with flat-lying major axes and a cumulative volume fraction of ca. 22%. Equant to sub-equant concretions are ubiquitous and occur at different heights within beds, often developing around marlstone rip-ups. Conversely, elongated concretions are either strata-bound concretions or completely cemented beds which become volumetrically dominant up section and off the channel axis. The interparticle pore-space of concretions represents on average ca. 22% and is tightly filled by poikilotopic and blocky calcite cement precipitated near to maximum burial depth, whereas host sandstones lack calcite cements and show smectite clay cement and an average preserved porosity of ca. 15%. The oxygen and carbon isotopes of calcite cements point to the marlstone as the main source of carbonate ions, suggesting concretions developed during burial by either diffusion from rip-ups and mud caps or recrystallization of, matrix micrite. Results suggest that the process by which the carbonate-rich component was eroded from the substrate and trapped within the channel-fill is a key control on spatial distribution of calcite concretions, likely to reflect on spatial variability of reservoir properties.

scholarly journals Stratigraphy of the Valanginian? to Early Paleocene succession in central Saudi Arabia outcrops: Implications for regional Arabian sequence stratigraphy

GeoArabia ◽  
2008 ◽  
Vol 13 (2) ◽  
pp. 51-86 ◽  
Author(s):  
Yves-Michel Le Nindre ◽  
Denis Vaslet ◽  
Sami S. Maddah ◽  
Moujahed I. Al-Husseini
Keyword(s):  
Saudi Arabia ◽  
Arabian Plate ◽  
Marine Fauna ◽  
Sequence Stratigraphic ◽  
Aruma Formation ◽  
Stratigraphic Position ◽  
Early Paleocene ◽  
Az Zabirah ◽  
Definition Of ◽  
Flooding Events

ABSTRACT On the basis of regional lithostratigraphic field mapping, and biostratigraphic and sequence stratigraphic interpretations, the definitions and ranks of the Late Valanginian? to Paleocene rock units that crop out in central Saudi Arabia were revised. The definition of the Late Valanginian? to Early Aptian Biyadh Sandstone is inconsistent with that of the same-named formation in subsurface Saudi Arabia. In outcrop, only the lower Dughum member of the Biyadh Sandstone corresponds to the subsurface Biyadh Sandstone. Accordingly, the Biyadh Sandstone at outcrop was redefined so as to correlate to the same-named subsurface formation; the term Dughum member is considered obsolete. Above the redefined Biyadh Sandstone, the Sallah Formation at outcrop (previously Sallah member of Biyadh Sandstone) yielded the Aptian and/or earliest Albian? ammonite Hypacanthoplites cf. milletianus d’Orbigny; it correlates (in part or completely) to the undifferentiated-Aptian Shu’aiba Formation in Abu Jifan field. The overlying Huraysan Formation (previously Huraysan member of Biyadh Sandstone) is assigned an Albian age based on its stratigraphic position above the Sallah Formation and below the Upper Albian and Cenomanian Majma Formation (previously Majma member of Wasia formation). The Huraysan Formation correlates by stratigraphic position and lithology to the Khafji and Safaniya members of the Wasia Formation in subsurface Saudi Arabia. The Majma Formation may correlate to the Mauddud, Wara and lower part of the Ahmadi members of the subsurface Wasia Formation in Saudi Arabia. The successively overlying Qibah and Malihah formations (previously Qibah and Malihah members of Wasia formation) complete the Cenomanian and Early Turonian succession below the pre-Aruma unconformity. These two formations may correlate to the upper part of the Ahmadi, Rumaila and Mishrif members of the subsurface Wasia Formation in Saudi Arabia. In central Saudi Arabia, the pre-Aruma unconformity is overlain by the Upper Campanian and Lower Maastrichtian Khanasir Member of the Aruma Formation. The Upper Maastrichtian Hajajah and Paleocene Lina members form the upper part of the Aruma Formation. In contrast, the subsurface Aruma Formation in Saudi Arabia may extend to the Coniacian Stage. The Biyadh Sandstone consists of coastal-plain clastics deposited during several transgressive-regressive sequences. It overlies the pre-Biyadh unconformity, which is represented by west-cutting regional erosion that reaches down to the Jurassic Dhruma and underlying Marrat formations. The overlying Sallah Formation represents a transgressive-regressive sequence deposited in lagoonal and tidal settings, and includes limestone beds with marine fauna. The overlying Huraysan Formation consists of fluvial, fining-upward clastics and is, together with older units, regionally eroded by the pre-Majma unconformity. The associated pre-Majma hiatus probably occurred in the Late Albian and is characterized by the Az Zabirah Bauxite, a deposit that reflects a pedogenic episode that occurred in tropical humid conditions. The fluvial and marginal marine clastics of the Majma Formation, and marine clastics and carbonates of the Qibah Formation, can together be characterized in terms of three flooding events. The Malihah Formation was deposited in mixed proximal settings (tidal to fluvio-deltaic) and exposed (paleosols with bauxite). It represents a regression associated with the eastward tilting of the Arabian Plate during Turonian tectonism along the Neo-Tethyan margin. Central Saudi Arabia remained exposed during the Late Turonian through Middle Campanian, during which times the pre-Aruma Bauxite formed. The Aruma Formation is characterized by four third-order sequences; one in the Khanasir Member, two in the Hajajah Member – all of Late Cretaceous age, and the Paleogene Lina sequence.

scholarly journals Early to mid-Cretaceous mixed carbonate-clastic shelfal systems: examples, issues and models from the Arabian Plate

GeoArabia ◽  
2002 ◽  
Vol 7 (3) ◽  
pp. 541-598 ◽  
Author(s):  
Roger B. Davies ◽  
David M. Casey ◽  
Andrew D. Horbury ◽  
Peter R. Sharland ◽  
Michael D. Simmons
Keyword(s):  
Saudi Arabia ◽  
Passive Margin ◽  
Arabian Plate ◽  
Carbonate Platforms ◽  
Carbonate Production ◽  
Sequence Stratigraphic ◽  
Stratigraphic Model ◽  
Depositional Systems ◽  
Migration Pathways ◽  
Mixed Carbonate

ABSTRACT Maximum Flooding Surfaces (MFS) in the Early to mid-Cretaceous mixed carbonate-clastic shelfal systems of the Arabian Plate have been incorporated into a new sequence stratigraphic model that links Kuwait, Iran, Saudi Arabia, Qatar, and the United Arab Emirates, to Oman and Yemen. It is based on regional sequence stratigraphic concepts supported by biostratigraphic, sedimentological and mineralogical data. The model has amended the positions of some existing MFS. The diachronous interplay between large-scale, proximal clastic systems and outboard (down-systems-tract) carbonate platforms was emphasized by concentrating on the depositional history of prodelta areas during delta advance and retreat. The prodelta area of relatively deep water separating the depositional systems has been termed the ‘Migratory Carbonate Suppressed Belt’ (MCSB). The model proposes that platform limestones expanded back over preceding prodelta areas during transgressions. The most extensive transgressions ultimately led to the demise of MCSBs. The maximum landward retreat of the shoreline coincided with the cessation of clastic input in the most up-systems-tract localities. Thus, the model has predicted that in many places MFS are located in the basal parts of clean carbonates even though these are not the deepest-water sediments. Examples are the Zubair-Shu’aiba (K70 MFS) and the upper Burgan-Maddud (K100) sections of the northern Gulf. Where carbonate platforms did not expand completely across the MCSBs, perhaps because of fault-control, the MCSBs survived and MFS are present within deeper-water, prodelta shales deposited below the most efficient window for carbonate production. Examples are the K40 to K60 MFS in intraformational shales of the Zubair, Biyadh, and Qishn formations of Kuwait, Saudi Arabia, and Yemen, and K100 in the Burgan-Wasia formations of Kuwait and Saudi Arabia. Even in these cases, the MFS are present within limestones deposited further down-systems-tract, notably in Iran (K60—Khalij Member, Gadvan Formation; K100—Dair Limestone Member, Burgan-Kazhdumi formations). Deeper-water dense limestones and shales with accompanying MFS were deposited along the northeastern passive margin of the Arabian Plate, or within intrashelf basins with some limited connection to the open ocean. From a regional perspective it can be seen that eustatic or tectonically forced MFS do not necessarily occur within the deepest-water facies. A regional understanding is needed for a more precise sequence stratigraphic interpretation of the Early to mid-Cretaceous succession of the Arabian Plate. The identification of the stratigraphic architecture is of major economic importance at the reservoir scale, for instance in recognizing vertical permeability and transmissibility barriers, as well as at the regional-play fairway scale in the distribution of seals and their potential influence on migration pathways. Our interpretations are also relevant to the prediction of source-rock distributions and, in the longer term, may help identify stratigraphic trap potential related to the interplay between clastic and carbonate depositional systems. Although the model proposed relates to the Arabian Plate, general conclusions may be applicable to other regions where mixed carbonate-clastic systems are well developed, for example in many basins of Tertiary age in South East Asia.

scholarly journals The Influence of Magmatic Intrusions on Diagenetic Processes and Stress Accumulation

Geosciences ◽  
2019 ◽  
Vol 9 (11) ◽  
pp. 477 ◽  
Author(s):  
Magnhild Sydnes ◽  
Willy Fjeldskaar ◽  
Ivar Grunnaleite ◽  
Ingrid Fjeldskaar Løtveit ◽  
Rolf Mjelde
Keyword(s):  
Numerical Study ◽  
Sedimentary Basins ◽  
Reservoir Quality ◽  
Hydrocarbon Migration ◽  
Hydrocarbon Reservoir ◽  
Hydrocarbon Traps ◽  
Diagenetic Processes ◽  
Porosity And Permeability ◽  
Magmatic Intrusions ◽  
Stress Accumulation

Diagenetic changes in sedimentary basins may alter hydrocarbon reservoir quality with respect to porosity and permeability. Basins with magmatic intrusions have specific thermal histories that at time of emplacement and in the aftermath have the ability to enhance diagenetic processes. Through diagenesis the thermal conductivity of rocks may change significantly, and the transformations are able to create hydrocarbon traps. The present numerical study quantified the effect of magmatic intrusions on the transitions of opal A to opal CT to quartz, smectite to illite and quartz diagenesis. We also studied how these chemical alterations and the sills themselves have affected the way the subsurface responds to stresses. The modeling shows that the area in the vicinity of magmatic sills has enhanced porosity loss caused by diagenesis compared to remote areas not intruded. Particularly areas located between clusters of sills are prone to increased diagenetic changes. Furthermore, areas influenced by diagenesis have, due to altered physical properties, increased stress accumulations, which might lead to opening of fractures and activation/reactivation of faults, thus influencing the permeability and possible hydrocarbon migration in the subsurface. This study emphasizes the influence magmatic intrusions may have on the reservoir quality and illustrates how magmatic intrusions and diagenetic changes and their thermal and stress consequences can be included in basin models.

scholarly journals Late Oxfordian micropalaeontology, nannopalaeontology and palaeoenvironments of Saudi Arabia

GeoArabia ◽  
2008 ◽  
Vol 13 (2) ◽  
pp. 15-46 ◽  
Author(s):  
Geraint Wyn ap Gwilym Hughes ◽  
Osman Varol ◽  
Mokhtar Al-Khalid
Keyword(s):  
Saudi Arabia ◽  
Carbonate Platform ◽  
Low Cost ◽  
Seismic Survey ◽  
Arabian Plate ◽  
Equatorial Position ◽  
Depositional Sequence ◽  
Hydrocarbon Reservoir ◽  
Potential Source Rock ◽  
Basin Margin

ABSTRACT The Hanifa Formation in Saudi Arabia consists of a succession of carbonates, over 100 m thick, that were deposited during the Late Jurassic in an equatorial position on the west flank of the Neo-Tethys Ocean. It consists of the Hawtah and overlying Ulayyah members, each of which is considered as a third-order depositional sequence. The Hawtah Member is assigned an ?Early to Mid-Oxfordian age, based on brachiopod, nautiloid and coccolith evidence; ammonite, nautiloid, coccolith and foraminiferal evidence indicate a Late Oxfordian age for the Ulayyah Member. A detailed study of the microbiofacies and lithology of the late highstand succession of the Ulayyah member sequence was conducted in 41 cored wells distributed across Saudi Arabia. The aim of the study was to determine the most likely locations for porous and permeable grainstone lithofacies that host the Hanifa Reservoir in the region. A range of palaeoenvironments has been determined which include shallow-lagoon packstones and foraminiferal-dominated grainstones and deep-lagoon wackestones and packstones with Clypeina/Pseudoclypeina dasyclad algae. In addition, a series of basin-margin, shoal-associated biofacies are present that include stromatoporoid back-bank packstones and grainstones with the branched stromatoporoid Cladocoropsis mirabilis, bank-crest grainstones with encrusting and domed stromatoporoids. A few wells also proved the presence of intra-shelf, basin-flank mudstones and wackestones containing tetraxon sponge spicules, deep-marine foraminifera and coccoliths. The Hanifa Formation demonstrates the high environmental sensitivity of the Oxfordian biocomponents in Saudi Arabia. The study has exploited this feature to interpret the regional Late Oxfordian palaeoenvironmental variations, together with inferred hydrocarbon implications, with a moderately high degree of certainty. This essentially micropalaeontologically based study has revealed the approximate limit of an intra-shelf basin, with an irregular margin, located in the east-central part of the Saudi Arabian portion of the Late Oxfordian Arabian Plate carbonate platform. The basin is flanked by a belt of stromatoporoid banks that pass laterally into a back-bank facies before developing into a lagoonal facies. There is no evidence for shoreline of this basin, although the presence of rare charophytes, wood fragments and quartz grains in the northwest testifies to possible proximity of fluviatile input. The grainstone-dominated basin-margin facies presents good hydrocarbon reservoir facies and its juxtaposition to intra-shelf, potential source-rock basinal sediments provides important new exploration prospects in areas hitherto uninvestigated for hydrocarbon reservoirs, for which the overlying Jubaila Formation provides an efficient regional seal. The study provides a template for low-cost, high-value guidance for the selection of seismic survey sites in remote, under-explored areas where only a few wildcat well samples are available. The study could also be performed using cuttings samples where cores are not available. The varied biofacies within the Hanifa Formation could be applied for biosteering applications should this tool become necessary in coiled-tube, underbalanced horizontal development wells.

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