Letteratura scientifica selezionata sul tema "Cementation (Petrology)"

Based on Archie’s cementation factor as measured on North Sea chalk and on published data, we explore how the cementation factor depends on other physical properties of the chalk. A relationship between cementation factor and specific surface with respect to bulk volume is obtained for chalk. This leads to how Archie’s cementation factor may be predicted from porosity and permeability for chalk as well as for sandstone. A common relationship between cementation factor and specific surface with respect to bulk volume calculated from porosity and permeability is obtained. As an alternative, the [Formula: see text]-factor in Archie’s equation is related to specific surface with respect to bulk volume, but the relationship is less clear than the simple relationship between cementation factor and specific surface.

A geometric factor properly describing the microstructure of a rock is compulsory for effective medium models to accurately predict the elastic and electrical rock properties, which, in turn, are of great importance for interpreting data acquired by seismic and electromagnetic surveys, two of the most important geophysical methods for understanding the earth. Despite the applications of cementation exponent for the successful modeling of electrical rock properties, however, there has been no demonstration of cementation exponent as the geometric factor for the elastic rock properties. We have developed a workflow to model the elastic properties of clean and normal granular rocks through the combination of effective medium modeling approaches using cementation exponent as the geometric factor. Based on the dedicated modeling approaches, we find that cementation exponent can be adequately used as a geometric factor for the elastic properties of granular rocks. Further results highlight the effects of cementation exponent on the elastic and joint elastic-electrical properties of granular rocks. The results illustrate the promise of cementation exponent as a geometric link for the joint elastic-electrical modeling to better characterize the earth through integrated seismic and electromagnetic surveys.

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.

We determine the acoustic velocities for samples cored from the Jauf and Unayzah sandstone formations of Saudi Arabia. We use microstructural analysis including thin sections and point counting to quantify cementation. Velocities in these formations are strongly controlled by the combination of porosity and cementation. Consequently, rocks of similar porosity but with different cementation materials display different velocities. The objective of this study is to understand the effect of cementation on the acoustic velocity. Cements in these two formations have variable compositions and properties. Pure quartz overgrowth plays a major role in increasing velocities while clay and clay coatings play a minor role. We found that clay coatings inhibit the quartz overgrowth cement leading to a decrease in velocities. Understanding the influence of various cementation types on velocity, and thus elastic properties in sandstone cores, enables an understanding of the variation of sonic velocities and moduli across these formations. The uniqueness of this study is that we emphasize the quantification of the role of cement and not just mineral volume.

Laboratory permeability data from the brine-filled Tubåen Formation in the Snøhvit field show an order of magnitude permeability variation for approximately the same porosity. This variation in permeability is explained by a modified Kozeny-Carman equation that exploits the relationships among permeability, porosity, cementation, and pore geometry. The expression correlates the slope in a logarithmic plot of porosity versus permeability with the amount of contact cement and sorting, and the intercept with the grain size. Additional information about sorting and/or cementation can be used to better constrain the slope of the plot. Based on this equation, we found that the grain size and the amount of contact cement increased with depth in the lowermost Tubåen 1–3 sandstone units, this led to an increasing permeability with depth, in the same porosity range. The permeability variation in the shallowest Tubåen 4 sandstone unit was affected by sorting to a larger degree than the remaining Tubåen intervals, which influenced the cementation factor, porosity, and permeability simultaneously. These findings were supported by the depositional environment of the formation, a petrology study of grain size and sorting and a rock-physics study. The rock-physics study indicated that the samples with higher permeability had higher elastic moduli compared with the samples with lower permeability. This correlation between permeability and elastic moduli can be explained by the increasing amount of contact cement for the stiffer, high-permeability samples.

AbstractIn the Troms 1 area, sediments of Early to Middle Jurassic age, ranging from alluvial plain deposits at the base, passing through coastal plain/tidal flat sediments up into high-energy nearshore shallow-marine sands, mark a transgression. The sandstones, classified as mineralogically and texturally mature quartz-arenites, are potential reservoir rocks in the eastern part of the area. The apparent supermaturity, however, is of secondary origin because unstable detrital components were dissolved during diagenesis. The succession of complex diagenetic processes was: (i) mechanical compaction and simultaneous pressure solution, (ii) partial dissolution with corrosion of detrital quartz and dissolution of unstable fragments, (iii) silica cementation, (iv) calcite cementation, (v) partial carbonate dissolution, (vi) kaolinite/Fe-carbonate cementation in the remaining pore space. Porosity and permeability of the sandstones are controlled by the degree of silicification and by dissolution processes. Two dissolution stages led to partial ‘skeletonization’ of the detrital framework and to elimination of unstable detrital grains. The first stage was a basic process leading to corrosion of detrital quartz and creating transitory secondary porosity; the second stage was acidic leading to the present preserved secondary porosity. Diagenetic dissolution channels formed. The degree of diagenetic alteration was much higher than normally observed in sandstones of such burial depth. Hydrothermal solutions rising from deep-seated faults may have led to this unusual alteration and triggered a rift-related type of complex diagenesis.

Includes bibliographical references (leaves 153-157). Petrographic image analysis proved particularly useful in determining the parameters for statistical analysis for the simple mineralogies displayed in the samples from the Hutton Sandstone. Concentrates on establishing techniques for statistical study of data collected by PIA to subdivide the framework grains from the porosity or cement.

Thesis (M. Phil.)--Hong Kong University of Science and Technology, 2004.
Includes bibliographical references (leaves 163-170). Also available in electronic version. Access restricted to campus users.

Gas hydrate is a naturally occurring crystalline compound formed by water molecules and encapsulated gas molecules. The interest in gas hydrate reflects scientific, energy and safety concerns - climate change, future energy resources and seafloor stability. Gas hydrates form in the pore space of sediments, under high pressure and low temperature conditions. This research focuses on the fundamental understanding of hydrate bearing sediments, with emphasis on mechanical behavior, thermal properties and lens formation. Load-induced cementation and decementation effects are explored with lightly cemented loose and dense soil specimens subjected to ko-loading; the small-strain stiffness evolution inferred from shear wave velocity measurement denounces stiffness loss prior to structural collapse upon loading. Systematic triaxial tests address the intermediate and large strain response of hydrate bearing sediments for different mean particle size, applied pressure and hydrate concentration in the pore space; hydrate concentration determines elastic stiffness and undrained strength when Shyd>45%. A unique sequence of particle-level and macro-scale experiments provide new insight into the role of interparticle contact area, coordination number and pore fluid on heat transfer in particulate materials. Micro-mechanisms and necessary boundary conditions are experimentally analyzed to gain an enhanced understanding of hydrate lens formation in sediments; high specific surface soils and tensile stress fields facilitate lens formation. Finally, a new instrumented high-pressure chamber is designed, constructed and field tested. It permits measuring the mechanical and electrical properties of methane hydrate bearing sediments recovered from pressure cores without losing in situ pressure (~20MPa).

The aim of this thesis is to study water saturation models available in the literature and to apply a proper one to a real field case. Archie equation is the most well-known water saturation model. However, it is formulated on some assumptions and is applicable to only clean sands. Archie equation cannot be used for shaly formation. There are many shaly water saturation models that account for shale effect for water saturation estimation. In this study, 3 wells, namely Well-01, Well-02 and Well-03 are studied. These wells lie in a fractured carbonate reservoir located in Southeastern part of Turkey. From well log recordings, the production formation is seen almost clean. In other words, the shale amount of the formation is so small that it can be neglected. Thus, to calculate the water saturation in those wells, the well-known Archie water saturation equation is used. Since the formation is fractured carbonate, the cementation factor (m ) and saturation exponent (n ) of conventional value of 2 each cannot be used for the water saturation calculation. Instead, these parameters are obtained from generalized crossplot of log-derived porosity and resistivity technique. Finally, each well is divided into zones using porosity data. Zonation is conducted based on statistical method, ANOVA (analysis of variance). Well-01 and Well-02 are both divided into two zones. On the other hand, the statistical method was initially divided Well-03 into three zones. However, Well-03 is better described as a whole zone, depending on the geological analysis and engineering judgment. After the zonation, the zones are correlated from well to well. The water saturations in significantly correlated zones are examined. Also, using the same statistical method, the water saturation zones are identified. However, these zones do not coincide with the porosity zones. This difference is attributed to pore size distribution and wettability which affect saturation distribution.

Carbon capture and storage (CCS) has been proposed as a potential technology to mitigate climate change. However, there is currently a huge gap between the global CCS deployment and that which will be ultimately required. To date, CCS deployment has been restricted to the most favourable tectonic settings, such as extensional passive margin and post-rift basins and compressional foreland basins. In addition, CCS deployment has stalled in most countries, with only limited commercial projects realised mainly in hydrocarbon-rich countries for enhanced oil recovery. This Ph.D. thesis aims to assess the potential of CCS development in compressional basins and hydrocarbon-limited regions at different scales: from a global-scale assessment to a national-scale assessment in Spain and finally, to a reservoir-scale analogue case study, focusing on the Puig-reig anticline (SE Pyrenees). Compressional settings host some of the most significant oil and gas resources in the world and will be key to the large-scale deployment of CCS. On the global scale, we present an integrated source-to-sink analysis tool that combines basin distribution, hydrocarbon resources and CO2 emissions to assess the potential of compressional basins for CCS development. This methodology allows identifying five high-priority regions for prospective CCS development in compressional basins: North America, north-western South America, south-eastern Europe, the western Middle East and western China. The results indicate that compressional basins will have to play a critical role in the future of CCS if this technology is to be implemented worldwide. Instead of developing CCS via CO2 enhanced oil recovery (CO2-EOR), hydrocarbon-limited countries need to devise alternative strategies if they intend to implement CCS in their decarbonisation strategies. On the national scale, we present a novel systematic source-to-sink assessment methodology based on a hubs and clusters approach to identify favourable regions for CCS deployment in hydrocarbon-limited countries. Throughout the evaluation of the Spanish case study, we identify 15 emission hubs from the power and the hard-to-abate sectors and priority source- to-sink clusters, based on screening and ranking processes using a multi-criteria decision-making method. North-Western and North-Eastern Spain are recognised as priority regions due to resilience provided by different types of CO2 sources and multiple geological storage structures. CCS, especially in the hard-to-abate sector, and in combination with other low-carbon energies, remains a significant contributor to the Paris Agreement’s mid-century net-zero target. This methodology can attract renewed public and political interest in viable deployment pathways of CCS in hydrocarbon-limited countries. The Ebro Foreland Basin, identified as one of the most potential areas for CCS development in Spain, is a typical hydrocarbon-limited compressional basin with low availability of geological and geophysical data required for the suitability assessment for CO2 storage. In this work, we carry out an integrated study of the Puig-reig anticline (SE Pyrenees) to be used as an outcrop analogue to explore the reservoir potential of foreland basin margin sedimentary systems. This anticline exposes continuous outcrops deposited in a proximal to medial fluvial fan system with an overall southeast downstream trend. The proximal deposits, mainly spreading in the northwest portion of the anticline, are characterised by conglomerates with minor interbedded sandstones. These are interpreted as having been deposited from unconfined flash floods and wide-shallow channel streams. The medial deposits, covering the rest of the anticline, consist of interbedded beds of conglomerates, sandstones and claystones, deposited in braided channel streams and overbanks. In order to understand the fracture distribution in the Puig-reig anticline and how it can potentially affect reservoir potential, fracture networks have been characterised using the linear scanline method, and four fracture sets (F1 to F4) have been identified in the target structure. The north limb shows low fracture intensity but large fracture length and aperture. The crest and the crest-limb transition zones present relatively high fracture intensity and variable fracture length and aperture. The south limb has low fracture intensity and small fracture length and aperture. Based on multiple linear regression analysis, we observe that fracture intensity is mainly controlled by the structural position, bedding thickness and lithological associations, with more intense fracturing in thin sandstone layers with multiple interlayers of fine deposits in the high strain zones. The fracture length mainly depends on bedding thickness and is affected by lithological associations. The fracture apertures are mainly controlled by lithofacies. An integrated analysis of structural, petrological and geochemical characteristics allows identifying five generations of calcite cements (Cc0 to Cc4) and fluid regimes in the Puig-reig anticline. Before intensive deformation, Cc0 precipitated in intergranular porosity from meteoric fluids in the phreatic zone. During the most intense phase of thrusting and folding, Cc1 precipitated in intergranular porosity, faults and F1 to F4 fracture sets from hydrothermal fluids migrated from the deep areas of the SE Pyrenees. During the late stage of fold growth, Cc2 mainly precipitated in normal and strike- slip faults in the anticline crest from the mixing between hydrothermal and meteoric fluids during the crestal collapse, or from hydrothermal fluids with shallower burial depth compared to that of Cc1. Cc3 mainly precipitated in faults and F1 and F4 fracture sets in the north-western zone of the anticline from formation fluids probably migrated through the frontal thrusts. During the continuous denudation, Cc4 precipitated in the reopened F1 to F4 fracture sets from meteoric fluids. The comparison of the Puig-reig anticline with other similar depositional and tectonic settings worldwide allows exploring the reservoir potential for CO2 storage at foreland basin margins. In the Puig-reig anticline, the proximal to medial deposits present low porosity of host rocks due to the prevailing presence of calcite cement, with limited high porosity concentrated in massive medium and coarse lithofacies in the medial fluvial fan. Sandstone lithofacies deposited from the medial fluvial fan and located in the high strain zones feature relatively high fracture intensity, which have relative high potential to be effective reservoirs. The study conducted in the Puig-reig anticline provides a conceptual model useful to understand the reservoir characteristics at the basin margins. According to this model, the reservoir potential is comprehensively controlled by sedimentology, diagenesis and deformation. The effective combination of both structure and facies can make basin margin locations potential areas for effective reservoirs, even in the presence of overall low porosity. Future work will focus on building a static reservoir model of the Puig-reig anticline based on the results obtained in the sedimentology, fracture and diagenesis studies, and finally carrying out fluid flow simulations to determine the main controls on CO2 injection and storage in such a geological setting.
La captura i emmagatzematge de carboni (CCS) s’ha proposat com una tecnologia potencial per mitigar el canvi climàtic. No obstant això, actualment hi ha una enorme bretxa entre el desplegament global de CCS i el que finalment serà necessari. Fins ara, el desplegament de CCS s’ha restringit a les configuracions tectòniques més favorables, com ara marges passius extensius, conques post-rift i conques d’avantpaís compressives. A més, el desplegament de CCS s’ha estancat a la majoria de països, amb pocs projectes comercials realitzats principalment a països rics en hidrocarburs per millorar la recuperació del petroli. Aquesta tesi doctoral té com a objectiu avaluar el potencial de desenvolupament de CCS en conques de compressió i regions sense hidrocarburs a diferents escales: des d’una avaluació a escala mundial fins a una avaluació a escala nacional a Espanya i, finalment, a l’estudi d’un analeg a escala de dipòsit, l’anticlinal de Puig-reig (SE Pirineus). Els entorns compressius contenen alguns dels reservoris de petroli i gas més importants del món i seran claus per al desplegament a gran escala de CCS. A escala mundial, presentem una eina d’anàlisi integrada que combina la distribució de la conca, els recursos d’hidrocarburs i les emissions de CO2 per avaluar el potencial de les conques compressives per al desenvolupament de CCS. Aquesta metodologia ens ha permès identificar cinc regions d’alta prioritat per al desenvolupament potencial de CCS a les conques compressives: Amèrica del Nord, nord-oest d’Amèrica del Sud, sud-est d’Europa, l’Oest de l’Orient Mitjà i l’oest de la Xina. Els resultats indiquen que les conques compressives hauran de tenir un paper crític en el futur de la CCS si aquesta tecnologia s’implementa a tot el món. En lloc de desenvolupar CCS mitjançant la recuperació del petroli (CO2-EOR), els països que tenen pocs hidrocarburs han d’elaborar estratègies alternatives si tenen la intenció d’implementar CCS en les seves estratègies de descarbonització. A escala nacional, presentem una nova metodologia sistemàtica d’avaluació basada en “centres i clústers” per identificar les regions favorables al desplegament de CCS als països amb pocs hidrocarburs. Aquesta eina l’hem aplicat en un cas de l’estat espanyol, on identifiquem 15 centres d’emissions en sectors de producció d’energia i d’indústries difícils d’abatre i s’han dissenyat els clústers prioritaris de font-embornal, basats en processos de selecció i classificació mitjançant un mètode de presa de decisions multicriteri. El nord- oest i el nord-est d’Espanya s’han identificat com les regions prioritàries degut a la resiliència que els hi proporciona diferents tipus de fonts de CO2 i múltiples estructures d’emmagatzematge geològic. El CCS, especialment per descarbonitzar el sector difícil de reduir, i en combinació amb altres energies de baixes emissions en carboni, continua sent un contribuent significatiu a l’objectiu de emissions zero netes per mitjans d’aquest segle segons l’Acord de París. Aquesta metodologia que presentem pot atreure un interès públic i polític renovat sobre aquesta tecnologia, en especial en els països amb pocs hidrocarburs. La conca d’avantpaís de l'Ebre, identificada com una de les àrees potencials per al desenvolupament de CCS a Espanya, és una conca compressiva típica amb poc interès pels hidrocarburs i, per tant, amb baixa disponibilitat de dades geològiques i geofísiques necessàries per a l'avaluació de la idoneïtat per a l'emmagatzematge de CO2. En aquest treball, realitzem un estudi integrat de l’anticlinal de Puig-reig (SE Pirineus) per utilitzar-lo com un anàleg en superfície per explorar el potencial de les conques sedimentaries d’avantpaís per l’emmagatzemament de CO2. Aquest anticlinal exposa afloraments continus dipositats en un sistema de ventalls fluvials proximals a intermedis amb una tendència general descendent cap el sud-est. Els dipòsits proximals, que s’estenen principalment a la part nord-oest de l’anticlinal, es caracteritzen per conglomerats amb gresos intercalats. S’interpreta com si s’haguessin dipositat a partir d’inundacions instantànies no confinades i canals amples i de poca fondària. Els dipòsits de la zona intermèdia, que cobreixen la resta de l’anticlinal, consisteixen en capes interestratificades de conglomerats, gresos i argiles, dipositats en canals trenats i sobreeiximent dels canals. Per tal d’entendre la distribució de les fractures a l’anticlinal de Puig-reig i com aquestes poden afectar el potencial del reservori d’aquesta estructura, s’han caracteritzat les xarxes de fractures mitjançant el mètode de la línia d’escaneig lineal i s’han identificat quatre conjunts de fractures (F1 a F4). L'extrem nord de l’anticlinal presenta una intensitat de fractures baixa, però una gran longitud i obertura de les fractures. La cresta i les zones de transició entre la cresta i els flancs presenten una intensitat de fractures relativament alta i una longitud i una obertura de les fractures variables. L’extrem sud té una intensitat de fractures baixa i una longitud i una obertura de les fractures petites. Basat en l’anàlisi de regressió lineal múltiple, observem que la intensitat de la fractura està controlada principalment per la posició estructural, el gruix de les capes i les associacions litològiques, amb una fracturació més intensa en les capes fines de arenites amb múltiples capes de dipòsits fins a les zones de més deformació de l’anticlinal. La longitud de la fractura depèn principalment del gruix de les capes i es veu afectada per les associacions litològiques. Les obertures de les fractures estan controlades principalment per les litofàcies. Una anàlisi integrada de les característiques estructurals, petrològiques i geoquímiques permet identificar cinc generacions de ciments de calcita (Cc0 a Cc4) i de règim de fluids a l’anticlinal de Puig-reig. Abans de la deformació intensiva, Cc0 precipitava en la porositat intergranular a partir de fluids meteòrics a la zona freàtica. Durant la fase més intensa d’encavalcament i plegament, Cc1 va precipitar en porositat intergranular, falles i en els conjunts de fractures de F1 a F4 a partir de fluids calents migrats des de les zones profundes. Durant la fase tardana del creixement del plec, el Cc2 precipità principalment en falles normals i direccionals en la cresta de l´anticlinal a partir de la barreja entre fluids calents i meteòrics durant el col·lapse de la cresta o bé a partir de fluids calents però a una profunditat d’enterrament inferior a la de Cc1. Cc3 precipità principalment en falles i en els conjunts de fractures F1 i F4 a la zona nord-oest de l’anticlinal a partir de fluids de formació que probablement van migrar a través dels encavalcaments frontals. Durant la denudació contínua, Cc4 va precipitar en els conjunts de fractures reoberts de F1 a F4 a partir de fluids meteòrics. La comparació de l’anticlinal de Puig-reig amb altres zones del mon amb ambients deposicional i tectònics similars permet explorar el potencial de d’emmagatzematge de CO2 d’aquest tipus d’estructures en conques d’avantpaís. A l’anticlinal de Puig-reig, els dipòsits proximals a intermedis presenten una porositat baixa de les roques hostes a causa de la presència predominant de ciment de calcita, amb algunes zones de porositat més elevada concentrades en litofàcies massives de gra mig a groller de les zones intermèdies del ventall fluvial. Les litofàcies d’arenites dipositades en la zona intermèdia del ventall i situades a les zones major deformació presenten una intensitat de fractura relativament elevada, amb un potencial relativament elevat per ser dipòsits efectius. L’estudi realitzat a l’anticlinal de Puig-reig proporciona un model conceptual útil per entendre les característiques dels reservoris en els marges d’una conca. Segons aquest model, el potencial del reservori està controlat de manera exhaustiva per la sedimentologia, la diagènesi i la deformació. La combinació efectiva tant de l’estructura com de la fàcies pot fer de les zones del marge de la conca que siguin zones potencials com reservoris efectius, fins i tot en presència d’una porositat baixa. Els treballs futurs es centraran en la construcció d’un model estàtic del dipòsit de l’anticlinal de Puig-reig basat en els resultats obtinguts en els estudis de sedimentologia, fractures i diagènesi i, finalment, la realització de simulacions de flux de fluids per determinar els principals controls d’injecció i emmagatzematge de CO2 en aquests tipus de sistemes geològics sedimentaris.