Compaction of North-Sea Chalk by Pore-Failure and Pressure Solution in a Producing Reservoir

Keszthelyi, Dániel; Dysthe, Dag Kristian; Jamtveit, Bjørn

doi:10.3389/fphy.2016.00004

Cited by 22 publications

(19 citation statements)

References 43 publications

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“…If some of the overpressured fluid could escape due to seal failure, this would result in significant inelastic deformation due to increasing effective stress, similar to that observed in depleting chalk gas reservoirs (e.g. Keszthelyi, Dysthe, & Jamtveit, 2016). This combination of cementation and compaction could, therefore, create high-density geobodies of diagenetic origin.…”

Section: Diagenetic Geobodiesmentioning

confidence: 92%

“…Investigating these SCRs with the same methodology will provide further insights into the fluid migration history and potential fault-bound diagenesis within the chalk, but with hydrocarbon emplacement as an additional complicating factor. Production at the Tyra (DK) Valhall, Elgin, and Ekofisk fields (NO) has already led to significant compaction of the reservoir and seafloor subsidence (metre to decametre scale), and this is expected to increase with further production (Keszthelyi et al, 2016). The Ryan Anticline SCRs could provide a natural analogue to these fields, but where reservoir compaction is a result of overpressure loss because of top seal failure.…”

Section: Concepts In the Seismic Chalk Paradigmmentioning

confidence: 99%

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Seismic geomorphology and origin of diagenetic geobodies in the Upper Cretaceous Chalk of the North Sea Basin (Danish Central Graben)

et al. 2018

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Kilometre-scale geobodies of diagenetic origin have been documented for the first time in a high-resolution 3D seismic survey of the Upper Cretaceous chalks of the Danish Central Graben, North Sea Basin. Based on detailed geochemical, petrographic and petrophysical analyses, it is demonstrated that the geobodies are of an open-system diagenetic origin caused by ascending basin fluids guided by faults and stratigraphic heterogeneities. Increased amounts of porosity-occluding cementation, contact cement and/or high-density/high-velocity minerals caused an impedance contrast that can be mapped in seismic data, and represent a hitherto unrecognized, third type of heterogeneity in the chalk deposits in addition to the well-known sedimentological and structural features. The distribution of the diagenetic geobodies is controlled by porosity/permeability contrasts of stratigraphic origin, such as hardgrounds associated with formation tops, and the feeder fault systems. One of these, the Top Campanian Unconformity at the top of the Gorm Formation, is particularly effective and created a basin-wide barrier separating low-porosity chalk below from high-porosity chalk above (a Regional Porosity Marker, RPM). It is in particular in this upper high-porosity unit (Tor and EkofiskFormations) that the diagenetic geobodies occur, delineated by "Stratigraphy Cross-cutting Reflectors" (SCRs) of which eight different types have been distinguished. The geobodies have been interpreted as the result of: (i) escaping pore fluids due to top seal failure, followed by local mechanical compaction of highporous chalks, paired with (ii) ascension of basinal diagenetic fluids along fault systems that locally triggered cementation of calcite and dolomite within the chalk, causing increased contact cements and/or reducing porosity. The migration pathway of the fluids is marked by the SCRs, which are the outlines of highdensity bodies of chalk nested in highly porous chalks. This study, thus, provides new insights into the 3D relationship between fault systems, fluid migration and diagenesis in chalks and has important applications for basin modelling and reservoir characterization.---

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Section: Diagenetic Geobodiesmentioning

confidence: 92%

Section: Concepts In the Seismic Chalk Paradigmmentioning

confidence: 99%

Seismic geomorphology and origin of diagenetic geobodies in the Upper Cretaceous Chalk of the North Sea Basin (Danish Central Graben)

et al. 2018

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“…This distribution function adequately described pore size distribution measurements performed on North Sea chalk [ Japsen et al , ]. Using the above distribution as an input parameter, our model can be used to predict the compaction history of the producing Ekofisk field [ Keszthelyi et al , ].…”

Section: Model Descriptionmentioning

confidence: 94%

First principles model of carbonate compaction creep

2016

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Rocks under compressional stress conditions are subject to long‐term creep deformation. From first principles we develop a simple micromechanical model of creep in rocks under compressional stress that combines microscopic fracturing and pressure solution. This model was then upscaled by a statistical mechanical approach to predict strain rate at core and reservoir scale. The model uses no fitting parameter and has few input parameters: effective stress, temperature, water saturation porosity, and material parameters. Material parameters are porosity, pore size distribution, Young's modulus, interfacial energy of wet calcite, the dissolution, and precipitation rates of calcite, and the diffusion rate of calcium carbonate, all of which are independently measurable without performing any type of deformation or creep test. Existing long‐term creep experiments were used to test the model which successfully predicts the magnitude of the resulting strain rate under very different effective stress, temperature, and water saturation conditions. The model was used to predict the observed compaction of a producing chalk reservoir.

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“…This coupled evolution of flow field and microstructure through chemistry is far from being understood because of the difficulties in direct experimental observation (Noiriel, 2015) and in numerically handling mathematical models based on free boundary problems of partial differential equations (Chadam et al, 1986;Ortoleva et al, 1987;Szymczak and Ladd, 2012;Yang et al, 2016b). What further complicates the problem is the introduction of geomechanical effects (Jamtveit and Hammer, 2012;Keszthelyi et al, 2016;Røyne and Jamtveit, 2015). If a porous structure weakened by water-rock interactions cannot sustain the stress exerted by the formation and/or the flow field, it collapses and forms a new structure to reestablish mechanical stability.…”

Section: Introductionmentioning

confidence: 99%

Direct Observation of Coupled Geochemical and Geomechanical Impacts on Chalk Microstructure Evolution under Elevated CO₂Pressure

Yang

Hakim

Bruns

et al. 2018

ACS Earth Space Chem.

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The dissolution of porous media in a geologic formation induced by the injection of massive amounts of CO 2 can undermine the mechanical stability of the formation structure before carbon mineralization takes place. The geomechanical impact of geologic carbon storage is therefore closely related to the structural sustainability of the chosen reservoir as well as the probability of buoyance driven CO 2 leakage through caprocks. Here we show, with a combination of ex situ nanotomography and in situ microtomography, that the presence of dissolved CO 2 in water produces a homogeneous dissolution pattern in natural chalk microstructure. This pattern stems from a greater apparent solubility of chalk and therefore a greater reactive subvolume in a sample. When a porous medium dissolves homogeneously in an imposed flow field, three geomechanical effects were observed: material compaction, fracturing and grain relocation. These phenomena demonstrated distinct feedbacks to the migration of the dissolution front and severely complicated the infiltration instability problem. We conclude that the presence of dissolved CO 2 makes the dissolution front less susceptible to spatial and temporal perturbations in the strongly coupled geochemical and geomechanical processes. Graphical abstract

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Compaction of North-Sea Chalk by Pore-Failure and Pressure Solution in a Producing Reservoir

Cited by 22 publications

References 43 publications

Seismic geomorphology and origin of diagenetic geobodies in the Upper Cretaceous Chalk of the North Sea Basin (Danish Central Graben)

Seismic geomorphology and origin of diagenetic geobodies in the Upper Cretaceous Chalk of the North Sea Basin (Danish Central Graben)

First principles model of carbonate compaction creep

Direct Observation of Coupled Geochemical and Geomechanical Impacts on Chalk Microstructure Evolution under Elevated CO₂Pressure

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Compaction of North-Sea Chalk by Pore-Failure and Pressure Solution in a Producing Reservoir

Cited by 22 publications

References 43 publications

Seismic geomorphology and origin of diagenetic geobodies in the Upper Cretaceous Chalk of the North Sea Basin (Danish Central Graben)

Seismic geomorphology and origin of diagenetic geobodies in the Upper Cretaceous Chalk of the North Sea Basin (Danish Central Graben)

First principles model of carbonate compaction creep

Direct Observation of Coupled Geochemical and Geomechanical Impacts on Chalk Microstructure Evolution under Elevated CO2Pressure

Contact Info

Product

Resources

About

Direct Observation of Coupled Geochemical and Geomechanical Impacts on Chalk Microstructure Evolution under Elevated CO₂Pressure