Modelling porosity and permeability in early cemented carbonates

Cabonate-hosted hydrocarbon reservoirs will play an increasingly important role in the energy supply, as 60% of the world's remaining hydrocarbon resources are trapped within carbonate rocks. The properties of carbonates are controlled by deposition and diagenesis, which includes calcite cementation that begins immediately after deposition and may have a strong impact on subsequent diagenetic pathways. This thesis aims to understand the impact of early calcite cementation on reservoir properties through object-based modelling and Lattice Boltzmann ow simulation to obtain permeability. A Bayesian inference framework is also developed to quantify the ability of Lattice Boltzmann method to predict the permeability of porous media. Modelling focuses on the impact of carbonate grain type on properties of early cemented grainstones and on the examination of the theoretical changes to the morphology of the pore space. For that purpose process-based models of early cementation are developed in both 2D (Calcite2D) and 3D (Calcite3D, which also includes modelling of deposition). Both models assume the existence of two grain types: polycrystalline and monocrystalline, and two early calcite cement types specific to these grain types: isopachous and syntaxial, respectively. Of the many possible crystal forms that syntaxial cement can take, this thesis focuses on two common rhombohedral forms: a blocky form 01¯12 and an elongated form 40¯41. The results of the 2D and 3D modelling demonstrate the effect of competition of growing grains for the available pore space: the more monocrystalline grains present in the sample, the stronger this competition becomes and the lesser the impact of each individual grain on the resulting early calcite cement volume and porosity. The synthetic samples with syntaxial cements grown of the more elongated crystal form 40¯41 have lower porosity for the same monocrystalline grains content than synthetic samples grown following more blocky crystal form 01¯12. Moreover, permeability at a constant porosity is reduced for synthetic samples with the form 40¯41. Additionally, synthetic samples with form 40¯41 exhibit greater variability in the results as this rhombohedral form is more elongated and has the potential for producing a greater volume of cement. The results of the 2D study suggest that for samples at constant porosity the higher the proportion of monocrystalline grains are in the sample, the higher the permeability. The 3D study suggests that for samples with crystal form 01¯12 at constant porosity the permeability becomes lower as the proportion of monocrystalline grains increase, but this impact is relatively minor. In the case of samples with crystal form 40¯41 the results are inconclusive. This dependence of permeability on monocrystalline grains is weaker than in the 2D study, which is most probably a result of the bias of flow simulation in the 2D as well as of the treatment of the porous medium before the cement growth model is applied. The range of the permeability results in the 2D modelling may be artificially overly wide, which could lead to the dependence of permeability on sediment type being exaggerated. Poroperm results of the 2D modelling (10-8000mD) are in reasonable agreement with the data reported for grainstones in literature (0.1-5000mD) as well as for the plug data of the samples used in modelling (porosity 22 - 27%, permeability 200 - 3000mD), however permeability results at any given porosity have a wide range due to the bias inherent to the 2D flow modelling. Poroperm results in the 3D modelling (10 - 30, 000mD) exhibit permeabilities above the range of that reported in the literature or the plug data, but the reason for that is that the initial synthetic sediment deposit has very high permeability (58, 900mD). However, the trend in poroperm closely resembles those reported in carbonate rocks. As the modelling depends heavily on the use of Lattice Boltzmann method (flow simulation to obtain permeability results), a Bayesian inference framework is presented to quantify the predictive power of Lattice Boltzmann models. This calibration methodology is presented on the example of Fontainebleau sandstone. The framework enables a systematic parameter estimation of Lattice Boltzmann model parameters (in the scope of this work, the relaxation parameter τ ), for the currently used calibrations of Lattice Boltzmann based on Hagen-Poiseuille law. Our prediction of permeability using the Hagen-Poiseuille calibration suggests that this method for calibration is not optimal and in fact leads to substantial discrepancies with experimental measurements, especially for highly porous complex media such as carbonates. We proceed to recalibrate the Lattice Boltzmann model using permeability data from porous media, which results in a substantially different value of the optimal τ parameter than those used previously (0.654 here compared to 0.9). We augment our model introducing porosity-dependence, where we find that the optimal value for τ decreases for samples of higher porosity. In this new semi-empirical model one first identifies the porosity of the given medium, and on that basis chooses an appropriate Lattice Boltzmann relaxation parameter. These two approaches result in permeability predictions much closer to the experimental permeability data, with the porosity-dependent case being the better of the two. Validation of this calibration method with independent samples of the same rock type yields permeability predictions that fall close to the experimental data, and again the porosity-dependent model provides better results. We thus conclude that our calibration model is a powerful tool for accurate prediction of complex porous media permeability

Late Cenozoic extension in Limni Basin in northern Evia, Greece

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences, 2009.Cataloged from PDF version of thesis.Includes bibliographical references (p. 35-36).The Aegean region has undergone several episodes of extensional deformation from early Miocene to present time. Among the structures that accommodate extension are faults that bound and cut sediments within young fault-controlled sedimentary basins. The objective of this study is to add to constraints on the history of within the upper plate of the Hellenic subduction zone. In particular, this study is aimed at mapping and, eventually, dating sediments and related normal faults in the Limni-Istiea basin of northern Evia. Field mapping in the southern portion of this basin reveals eight sedimentary units and suggests several periods during which steep relief was formed within and adjacent to the basin, interspersed with periods of deposition in fluvial and shallow lacustrine environment. The three sets of faults identified in the mapped area are consistent with the orientation of structures observed at the western end of the North Aegean trough system and within the Central Hellenic shear zone. The oldest faults are low-angle, north-south trending and east-dipping; younger structures are high angle, west-east or southwest-northeast trending and generally south-dipping; the youngest faults are high-angle, northwest-southeast trending and dipping to the southwest. The paleomagnetic analyses results show clockwise rotation of the Limni- Istiea basin by 18° during or after the last stages of extension within the basin.by Aleksandra M. Hosa.S.M

Benchmarking worldwide CO₂ saline aquifer injections

Carbon Capture, Transport and Storage is a very active field of research, especially for the past decade. From the UK perspective, a commercially crucial aspect is the saline aquifer research, since there are predicted to be vast storage capacities in the sedimentary formations of the North Sea. The following report reviews the ongoing work on practical injections of CO2 as research tests for storage projects and specifically focuses on industrial sized saline aquifer injections.Carbon Capture, Transport and Storage is a very active field of research, especially for the past decade. From the UK perspective, a commercially crucial aspect is the saline aquifer research, since there are predicted to be vast storage capacities in the sedimentary formations of the North Sea. The following report reviews the ongoing work on practical injections of CO2 as research tests for storage projects and specifically focuses on industrial sized saline aquifer injections

Imaging of the Hellenic subduction zone by seismic tomography

Thesis: S.B., Massachusetts Institute of Technology, Department of Earth, Atmospheric, and Planetary Sciences, 2008.Cataloged from PDF version of thesis.Includes bibliographical references (pages 24-25).The Hellenic subduction zone is a complicated tectonic boundary, along which transitions in the nature of subducted material are believed to occur. The objective of this study was to better constrain the subsurface geometry of the Hellenic subduction zone by increasing the resolution of an existing tomographic model of the region. Increase in resolution is important for understanding the effects of inferred transitions in subducted material at depth. Nonlinear inversion of P-wave travel times was used on a global dataset expanded by temporary array data collected in southern Greece. Results show a vertically continuous slab, with a break at the depth 200-400 km detected only in the NW portion of the system. At depth above 400 kin, there is a lateral discontinuity marked by the Central Hellenic Shear Zone and Kephalonia Transform Fault, with slab more pronounced in southern part of the system. Our study supports the hypothesis of the change in subduction mode between northern and southern part of Hellenic arc in late Pliocene.by Aleksandra M. Hosa.S.B

Progressing Scotland's CO2 storage opportunities

Carbon capture, transport and storage (CCS) is a rapidly growing industry that offers both environmental benefits and substantial business, employment and research opportunities for Scotland and the UK. In 20091 the report Opportunities for CO2 storage around Scotland identified the size of these opportunities and key initiatives that need to be acted upon to move CCS forward in Scotland. Government, industry and stakeholder organisations joined with Scottish Carbon Capture and Storage (SCCS) researchers in this Scottish Carbon Capture and Storage Development Study to progress some of the actions needed to inform the deployment of the entire CCS chain in Scotland and the UK. The study presents new insights on: • A path to CCS, defining the activities and timescales to meet national and international ambitions for deployment of CCS and reduction of greenhouse gas emissions; • Scotland's CO2 storage assets, refining the estimated large-scale carbon dioxide (CO2) storage capacity in North Sea sandstones; • Skills and capacity needs for the future global CCS industry and how to realise opportunities it presents for UK economic development; • Public communication and engagement on CCS. A Path to Deployable CCS technologies was explored and mapped out by the study members in July 2009, prior to the commencement of the study. The path presents their view of the timescales and activities needed to implement CCS in Scotland which, adopted together with other low-carbon technologies, will contribute to the national target of 80% reduction of greenhouse gas emissions by 2050. This path has been adopted by the Scottish Government and Scottish Enterprise and has informed their document 'Carbon Capture and Storage - a Roadmap for Scotland' in 2010.Carbon capture, transport and storage (CCS) is a rapidly growing industry that offers both environmental benefits and substantial business, employment and research opportunities for Scotland and the UK. In 20091 the report Opportunities for CO2 storage around Scotland identified the size of these opportunities and key initiatives that need to be acted upon to move CCS forward in Scotland. Government, industry and stakeholder organisations joined with Scottish Carbon Capture and Storage (SCCS) researchers in this Scottish Carbon Capture and Storage Development Study to progress some of the actions needed to inform the deployment of the entire CCS chain in Scotland and the UK. The study presents new insights on: • A path to CCS, defining the activities and timescales to meet national and international ambitions for deployment of CCS and reduction of greenhouse gas emissions; • Scotland's CO2 storage assets, refining the estimated large-scale carbon dioxide (CO2) storage capacity in North Sea sandstones; • Skills and capacity needs for the future global CCS industry and how to realise opportunities it presents for UK economic development; • Public communication and engagement on CCS. A Path to Deployable CCS technologies was explored and mapped out by the study members in July 2009, prior to the commencement of the study. The path presents their view of the timescales and activities needed to implement CCS in Scotland which, adopted together with other low-carbon technologies, will contribute to the national target of 80% reduction of greenhouse gas emissions by 2050. This path has been adopted by the Scottish Government and Scottish Enterprise and has informed their document 'Carbon Capture and Storage - a Roadmap for Scotland' in 2010