Multiphase Extension Research Articles

Rift reactivation and migration during multiphase extension

Passive margins may undergo multiple phases of extension with distinct structural, petrological and sedimentary processes before achieving breakup. Observations of rift axis migration through time may reflect cooling, hardening and subsequent abandonment of the rift axis during either long-term periods of slow extension or periods of tectonic quiescence. Here, we use 2D thermo-mechanical numerical models to examine rift reactivation and migration during multiphase extension where a period of tectonic quiescence separates phases of extension. Our goals are to identify the rheological mechanism(s) controlling rift reactivation versus migration and determine if cooling phases may help explain recent interpretations of passive margin architecture and evolution. Our numerical experiments indicate that the relative integrated brittle strength between the initial rift and surrounding regions, rather than the total integrated strength, largely controls rift reactivation versus migration. The tectonic quiescence (cooling) duration required to induce rift migration ranges between 20 and 60 Myr (minimum bounds). This range reflects variations in extension velocity, magnitude of shear zone healing, crustal rheology and asthenospheric rheology. Reactivated rifts after extensive (>20 Myr) cooling periods in some cases develop asymmetric margins with deformation patterns stepping toward the future rift, such as characterizing most of the Atlantic conjugate margins.

Origin, structural geometry, and development of a giant coherent slide: The South Makassar Strait mass transport complex

The South Makassar Strait mass transport complex (MTC) covers an area of at least 9000 km 2 and has a total volume of 2438 km 3 . It is composed of a shale-dominated sedimentary unit with high water content. Seismic reflection data across the South Makassar Strait MTC show that it displays relatively coherent internal sedimentary stratigraphy that in the toe region is deformed into well-defined thrust-related structures (imbricates, ramps and flats, fault bend folds). It is one of the largest known coherent MTCs. The bowl-shaped central core region is as much as 1.7 km thick, and is confined to the west and east by 355° and 325° trending (respectively) lateral ramps in the upper slope area that pass via oblique ramps into a northeast-southwest–trending frontal ramp area. The core area passes via the lateral, oblique, and frontal ramps into an extensive, thin (tens of meters thick) region of the MTC (the lateral and frontal apron areas) that are internally deformed by thrusts, normal faults, and thrust faults reactivated as normal faults. The MTC anatomy can be divided into extension headwall, translational, toe, flank, lateral apron, and frontal apron domains. The headwall region is located in the upper slope area of the Paternoster platform; the main body of the slide is in the deep-water region of the Makassar Strait. The complex is interpreted to be triggered by uplift of the platform area (accompanied by inversion), and/or basin subsidence, which caused seaward rotation of ∼2° of the Paternoster platform in the Pliocene. Variable uplift promoted sliding dominantly from the eastern and western margins of the headwall. The internal fault patterns of the MTC show that extension in the upper slope to lower slope in the core area changes downslope to compressional structures in the toe domain and apron. Later extensional collapse of parts of the compressional toe area occurred with negative inversion on some faults. The coherent internal stratigraphy, and evidence for multiphase extension in the eastern headwall area, suggests that the ∼6–7 km of shortening in the toe region of the MTC occurred at a slow strain rate. Therefore, this type of MTC does not have the potential to generate tsunamis.

Continental extension and break-up—using the Australian margins as a case study

The continental margins of Australia provide an excellent natural laboratory for investigations of continental extension and break-up, with examples of failed rifts, multi-phase extensional systems, and volcanic and non-volcanic margins. The thick sedimentary cover across large parts, however, has hindered understanding of the deep crustal and lithospheric structure due to poor imaging. ION Geophysical has acquired deep, long offset seismic data across Australia’s North West Shelf, as well as the Bight Basin on Australia’s southern margin. These programs provide unique imaging of the deep basement structures and the complete overlying sedimentary section, and across all of the terrains from continental crust to oceanic crust. The authors’ interpretation of these data will be discussed in the context of existing models for continental extension and break-up and the resulting implications for the petroleum system: Models of hyper-extension and possible mantle exhumation will be discussed with regards to the Bonaparte, Browse and Bight basins. Multi-phase extension and the development of intra-sedimentary detachment horizons will be reviewed across many areas. Development of volcanic margins, including the effects of dynamic uplift and magmatic intrusions, will be investigated in the Exmouth Plateau. Creation of enough accommodation space to allow the deposition of the observed (~20 km) sedimentary sections in the Carnarvon and Bonaparte basins.

A Modified Level Set Approach for Segmentation of Multiband Polarimetric SAR Images

This paper investigates the application of a level set method for the automated multiphase segmentation of multiband and polarimetric synthetic aperture radar (SAR) images. The level set formulation is used to form an energy functional that includes the image statistical information defined on active contours. In addition to the classical Wishart/Gaussian distribution for locating region boundaries, edge information is incorporated into the energy functional to improve the performance of polarimetric data segmentation. An active contour model with an edge indicator is proposed by assuming that the image boundary term follows a Gibbs prior. An empirical parameter setting criterion is developed to ensure that the components of the energy functional are in proper proportion. We then investigate the multiphase extension for energy minimization, and we use a piecewise constant model to embed the proposed active contour model. Synthetic and real multiband polarimetric SAR data are used for verification. The experiments show that our method is superior to another level set method based on the Wishart/Gaussian distribution, in which SAR edge information is not included, particularly for discriminating among low-contrast regions. Furthermore, results also show that segmentation is improved when multiband data are used in the level set framework.

Strain migration during multiphase extension: Observations from the northern North Sea

Many rifts develop through multiphase extension; it can be difficult, however, to determine how strain is distributed during reactivation because structural and stratigraphic evidence associated with earlier rifting is often deeply buried. Using 2-D and 3-D seismic reflection and borehole data from the northern North Sea, we examine the style, magnitude, and timing of reactivation of a preexisting, Permian-Triassic (Rift Phase 1) fault array during a subsequent period of Middle Jurassic to Early Cretaceous (Rift Phase 2) extension. We show that Rift Phase 2 led to the formation of new N-S striking faults close to the North Viking Graben but did not initially reactivate preexisting Rift Phase 1 structures on the Horda Platform. We suggest that at the beginning of Rift Phase 2, strain was focused in a zone of thermally weakened lithosphere associated with the Middle Jurassic North Sea thermal dome, rather than reactivating extant faults. Diachronous reactivation of the Permian-Triassic fault network eventually occurred, with those faults located closer to the Middle Jurassic to Early Cretaceous rift axis reactivating earlier than those toward the eastern margin. This diachroneity may have been related to flexural down bending as strain became focused within the North Viking Graben, and/or the shifting of the locus of rifting from the North Sea to the proto-North Atlantic. Our study shows that the geometry and evolution of multiphase rifts is not only controlled by the orientation of the underlying fault network but also by the thermal and rheological evolution of the lithosphere and variations in the regional stress field.

On relative permeability data uncertainty and CO2 injectivity estimation for brine aquifers

Performance assessment of possible CO2 storage schemes is often investigated through numerical simulation of the CO2 injection process. An important criterion of interest is the maximum sustainable injection rate. Relevant numerical models generally employ a multi-phase extension to Darcy's law, requiring data concerning the evolution of relative permeability for CO2 and brine mixtures with increasing CO2 saturation. Relative permeability data is acutely scarce for many geographical regions of concern and often cited as a major source of uncertainty. However, such data is expensive and time consuming to acquire. With a view to improving our understanding concerning the significance of relative permeability uncertainty on injectivity, this article presents a sensitivity analysis of sustainable CO2 injection rate with respect to permeability, porosity and relative permeability. Based on available relative permeability data obtained from 25 sandstone and carbonate cores discussed in the literature, injectivity uncertainty associated with relative permeability is found to be as high as ±57% for open aquifers and low permeability closed aquifers (<50mD). However, for high permeability closed aquifers (>100mD), aquifer compressibility plays a more important role and the uncertainty due to relative permeability is found to reduce to ±6%.

A multiple-continuum model for simulating single-phase and multiphase flow in naturally fractured vuggy reservoirs

The existence of vugs or cavities in naturally fractured reservoirs has long been observed. Even though these vugs are known for their large attribution to reserves of oil, natural gas, or groundwater, few quantitative investigations of fractured vuggy reservoirs have been conducted. In this paper, a multiple-continuum conceptual model is presented, based on geological data and observations of core samples from carbonate formations in China, to investigate single-phase and multiphase flow behavior in such vuggy fractured reservoirs. The conceptual model has been implemented into a three-dimensional, three-phase reservoir simulator with a generalized multiple-continuum modeling approach. The conceptual model considers fractured vuggy rock as a triple- or multiple-continuum medium, consisting of (1) highly permeable and well-connected fractures, (2) low-permeability rock matrix, and (3) various-sized vugs. The matrix system may contain a large number of small or isolated cavities, whereas vugs are larger cavities, indirectly connected to fractures through small fractures, microfractures or matrix. Similar to the conventional double-porosity model, the fracture continuum is primarily responsible for the occurrence of global flow, while vuggy and matrix continua, providing storage space, are locally connected to each other and interacting with globally connecting fractures. In addition, flow in fractured vuggy reservoirs may be further complicated by occurrence of non-Darcy's and other nonlinear flow behavior, because of large pore space and high-permeability flow channels. To account for such complicated flow regime, our model formulation includes non-Darcy flow using the multiphase extension of the Forchheimer equation as well as flow according to parallel-wall fracture and tube models, based on solutions of flow through a parallel-wall, uniform fracture and Hagen–Poiseuille tube flow.

On Stability Testing Analysis in Phase Behavior Calculations

Stability testing analysis has become, in recent times, an area of major interest in phase equilibrium calculations. With particular concern to reservoir fluid phase behavior modeling, it has become the most important factor in developing robust algorithms and ensuring efficient calculations. We discuss the origin and systematic development of stability testing analysis as a necessary preliminary step in isothermal flash calculations. Its application to multicomponent multiphase reservoir fluids and extension prospects is also highlighted.

Cell Tracking using Coupled Active Surfaces for Nuclei and Membranes

An Insight Toolkit (ITK) processing framework for segmenting and tracking nuclei in time-lapse microscopy images using coupled active contours is presented in this paper. We implement the method of Dufour et al.[2] to segment and track cells in fluorescence microscopy images. The basic idea is to model the image as a constant intensity background with constant intensity foreground components. We utilizes our earlier submissions on the Chan and Vese algorithm [1] and its multiphase extension [5] to build our new tracking filter. The tracking filter itk::MultiphaseLevelSetTracking inputs a segmentation result (or a coarse estimate) from the previous time-point along with the feature image and generates a new segmentation output. By iteratively repeating this process across all time-points, real-time tracking is made possible. We include 2D/3D example code, parameter settings and show the results generated on a 2D zebrafish embryo image series.

Post-breakup compression of a passive margin and its impact on hydrocarbon prospectivity: An example from the Tertiary of the FaeroendashShetland Basin, United Kingdom

The FaeroeShetland Basin is part of a passive continental margin that formed as a result of multiphase extension associated with North Atlantic rifting during the Mesozoic and Paleocene. Breakup was followed by postrift subsidence during the latest Paleocene to late Eocene and the development of at least three 70–150-km (43–93-mi)-long, broadly north-south–orientated, slope canyons and linked terminal fans during the middle Eocene. The terminal fans filled northeast-southwest–striking basin-floor bathymetric depressions that had formed above the hanging walls of underlying, dormant northeast-southwest–trending Mesozoic extensional faults and adjacent half-graben depocenters. Compression during the middle and late Miocene caused contractional reactivation of the Mesozoic extensional faults and folding of the overlying uppermost Paleocene to middle Miocene postrift sediments into a series of 17 northeast-southwest–striking anticlinal domes. The switch from hanging-wall bathymetric depression during terminal fan deposition to anticlinal domal high during and after the middle to late Miocene compression has led to the present-day spatial coincidence of a potential hydrocarbon reservoir and an effective trap. The anticlines also acted as the foci for gas migration during or after compression (15 Ma to present). However, the timing of compression and differential uplift of the basin margins during the past 15 m.y., approximately 45 m.y. after the main phase of oil migration, may be a critical negative factor for oil exploration in this part of the basin. This hydrocarbon phase may have spilled during the structural reorganization, either updip into shallower traps or out of the hydrocarbon system via seeps.

Three phase cavitating flows in high-pressure swirl injectors

The internal combustion engine remains to be one of the most important sources of energy. The direct gasoline injection (DGI) is a new technology that promises considerable improvement of internal combustion engine efficiency. The key component in the DGI engine is its injection system. A three-phase flow simulation of the flow in the high-pressure swirl injector, typical for DGI engines, is presented here. The model is based on the multiphase extension of the two-fluid model. The most important characteristics of the flow were predicted. The results show the formation of a thin conical fuel sheet with an air core. Cavitation was also predicted in the pressure depression initiated in the air core. The presented approach seems to be very promising for the simulation of flows in DGI injectors.

Rheological controls on extensional styles and the structural evolution of the Northern Carnarvon Basin, North West Shelf, Australia

The extensional architecture of the Northern Carnarvon Basin can be explained in terms of changes in lithospheric rheology during multiphase extension and lower crustal flow. Low‐angle detachments, while playing a minor role, are not considered to have been the primary mechanism for extension as suggested in previous models. Early extension (Cambrian‐Ordovician) in the Northern Carnarvon Basin is characterised by low‐angle detachment structures of limited regional extent. These structures have a spatial association with a Proterozoic mobile belt on the margin of the Pilbara Craton. Thermo‐mechanical conditions in the mobile belt may have predisposed the highly deformed crust to thin‐skinned extension and detachment development. Permo‐Carboniferous extension generated an extensive wide rift basin, suggesting ductile rheologies associated with intermediate lithospheric temperatures and crustal thickness. Thick Upper Permian to Upper Triassic post‐rift sequences and marked thinning of the lower crust occurred in association with only a small amount of extension in the upper crust. This observation can be reconciled by considering outward lower crustal flow, from beneath the basin towards the basin margin, following extension. Strong mid‐crustal reflectors, which occur over large areas of the Northern Carnarvon Basin, probably represent a boundary between flow and non‐flow regimes rather than detachment fault surfaces as in previous models. Crustal thinning and thermal decay following Permo‐Carboniferous extension contributed to the increased strength and brittle behaviour of the lithosphere. Consequently, Late Triassic to Early Cretaceous extension resulted in the development of far more localised narrow rift systems on the margins of the preceding wide rift basin. Diapiric intrusions are associated with the narrow rift basin development, resulting from either remobilisation of ductile lower crustal rock or the initial formation of sea‐floor spreading centres.

Multi-phase compression and extension involving basement under the Colville Hills, Northwest Territories

Multi-phase compression and extension involving basement under the Colville Hills, Northwest Territories

The relationship between immiscible and miscible displacement in porous media

Displacement processes in porous media share several common characteristics. Fundamental among them is the representation of the momentum balance via Darcy’s law and its multiphase extension (Bear, 1972). Such description leads to systems of equations the solution of which parallels the behavior of the solution of processes in multicomponent chromatography. For instance, it has been recognized that noncapillary, multiphase displacement in one-dimensional (rectilinear or radial) porous media can be solved by techniques identical to those used in chromatographic transport (Helfferich, I98 I; Rhee et al., 1986, and references therein). This similarity arises naturally for the case of one-dimensional flow geometries and in the absence of dissipative terms (diffusion, dispersion, or capillarity), where both multiphase and multicomponent chromatography processes are formulated by systems of first-order hyperbolic equations. In this note we pursue further this relationship in mathematical representation between multiphase flow and chromatographic processes in porous media. Specifically, we consider two-phase, immiscible displacement and single-phase, miscible displacement in the presence of equilibrium adsorption. It is demonstrated that the two problems are mathematically equivalent, regardless of the dimensionality of the flow system and the presence of dissipative effects. Such an analogy is of practical importance in the analysis of various process characteristics, for instance in describing the evolution of unstable two-dimensional disturbances during viscous fingering. The latter is a topic of active current investigations (Homsy, 1987, and references therein), and of fundamental importance in process performance. Any similarities between seemingly different processes would be of considerable help in an effort to reduce complexity and to uncover common mechanisms. An extension to multiphase immiscible displacement and multicomponent miscible displacement is also briefly discussed. Mathematical Description