Salt tectonics is the study of how and why salt structures evolve and the three-dimensional forms that result. A fascinating branch of geology in itself, salt tectonics is also vitally important to the petroleum industry. Covering the entire scale from the microscopic to the continental, this textbook is an unrivalled consolidation of all topics related to salt tectonics: evaporite deposition and flow, salt structures, salt systems, and practical applications. Coverage of the principles of salt tectonics is supported by more than 600 color illustrations, including 200 seismic images captured by state-of-the-art geophysical techniques and tectonic models from the Applied Geodynamics Laboratory at the University of Texas, Austin. These combine to provide a cohesive and wide-ranging insight into this extremely visual subject. This is the definitive practical handbook for professional geologists and geophysicists in the petroleum industry, an invaluable textbook for graduate students, and a reference textbook for researchers in various geoscience fields.

Salt Tectonics: Principles and Practice

The Triassic Yanchang Formation contains the main oil-bearing strata in the Ordos Basin, central China. But the sedimentology of the Upper Triassic is still under debate, and flood-generated, hyperpycnal-flow deposits and their implications for unconventional petroleum development have long been overlooked. Our study indicates that hyperpycnites are well developed in the seventh oil member of the Yanchang Formation. They are characterized by couplets of upward-coarsening intervals and upward-fining intervals, separated by microscale erosion surfaces. The origination of hyperpycnal flows was controlled mainly by episodic tectonic movements and the humid climate. The deposits extend from distributary estuaries into the deep lake, have intercalations of dark shales and tuffs, and coexist with debrites and turbidites as a result of the progradation of subaqueous fans. The hyperpycnites have implications for unconventional petroleum reservoirs, because the flows supplied not only large amounts of coarse grains and organic material to the deep-water, fine-grained central lake sediments but also affected the ecosystems, resulting in a higher total organic carbon content in the sediments.

Climatic and tectonic controls of lacustrine hyperpycnite origination in the Late Triassic Ordos Basin, central China: implications for unconventional petroleum development

Genesis and character of thin-bedded turbidites associated with submarine channels

Lithofacies and origin of the Late Triassic muddy gravity-flow deposits in the Ordos Basin, central China

Adequate knowledge of the in situ state of stress can be essential to the analysis of geotechnical systems. However, the measurement and prediction of k0 remain difficult. In particular, limited attention has been given to the evolution of k0 during the formation history of the soil and diagenetic processes such as mineral dissolution. Experimental and numerical results show that grain mass loss due to mineral dissolution produces a pronounced horizontal stress drop under zero lateral strain conditions; the state of stress may reach the active shear failure ka condition and internal shear planes may develop. While horizontal stress recovery often follows upon further dissolution, marked differences in fabric are observed between the pre and postdissolution soil structures.

Mineral dissolution and the evolution of k0.

We compare four approaches to geomechanical modeling of stresses adjacent to salt bodies. These approaches are distinguished by their use of elastic or elastoplastic constitutive laws for sediments surrounding the salt, as well as their treatment of fluid pressures in modeling. We simulate total stress in an elastic medium and then subtract an assumed pore pressure after calculations are complete; simulate effective stress in an elastic medium and use assumed pore pressure during calculations; simulate total stress in an elastoplastic medium, either ignoring pore pressure or approximating its effects by decreasing the internal friction angle; and simulate effective stress in an elastoplastic medium and use assumed pore pressure during calculations. To evaluate these approaches, we compare stresses generated by viscoelastic stress relaxation of a salt sphere. In all cases, relaxation causes the salt sphere to shorten vertically and expand laterally, producing extensional strains above and below the sphere and shortening against the sphere flanks. Deviatoric stresses are highest when sediments are assumed to be elastic, whereas plastic yielding in elastoplastic models places an upper limit on deviatoric stresses that the rocks can support, so stress perturbations are smaller. These comparisons provide insights into stresses around salt bodies and give geoscientists a basis for evaluating and comparing stress predictions.

https://www.searchanddiscovery.com/documents/2011/40777luo/ndx_luo.pdf

Geomechanical modeling of stresses adjacent to salt bodies: Part 1—Uncoupled models

Modeling stress evolution around a rising salt diapir

We use a fully coupled poroelastoplastic geomechanical model to study how stresses and pore pressures evolve in sediments bounding a spherical salt body. Drained analyses (pore pressures remain hydrostatic) demonstrate that sediments yield in response to loading by the salt, which leads to a redistribution of stresses and to deformations larger than predicted by poroelastic or solid Coulomb-plastic models. Undrained analyses (overpressures develop while no dissipation occurs) illustrate that salt loading induces pore pressures that extend kilometers away from the salt body. We also model the flow and consequent dissipation that occur in the sediments because of this undrained salt loading. We show that with time, the pressure field dissipates and expands. The dissipation process takes millions of years, which suggests that pore-pressure perturbations caused by salt loading should still be present in mudstones near many salt bodies. Under drained conditions, stress perturbations generate low minimum principal stresses above and below the salt, resulting in convergence of pore pressure and minimum principal stress at these locations. Such conditions are challenging to drill through. In undrained systems, sharp drops in pore pressure may occur above and below the salt, whereas both the pore pressure and the minimum principal stress rise next to the salt. In contrast to previous models that do not couple changes in stress to changes in pore pressure, the coupled approach presented here has the potential to predict in-situ stresses and pore pressures more accurately in a wide variety of geologic settings.

Geomechanical modeling of stresses adjacent to salt bodies: Part 2—Poroelastoplasticity and coupled overpressures

This paper describes the application of a generalized effective stress soil model, MIT-S1, within a commercial finite-element program, for simulating the performance of the support system for the 20-m-deep excavation of the M1 pit adjacent to the primary station “Hauptbahnhof” in Berlin. The M1 pit was excavated underwater and supported by a perimeter diaphragm wall with a single row of prestressed anchors. Parameters for the soil model were derived from an extensive program of laboratory tests on the local Berlin sands. This calibration process highlights the practical difficulties both in the measurements of critical state soil properties and in the selection of model parameters. The predictions for excavation performance are strongly affected by the vertical profiles of two key state parameters: the initial earth pressure ratio, K0; and the in situ void ratio, e0. These parameters were estimated from field dynamic penetration test data and geological history. The results showed good agreement between c...

Maria-Aikaterini Nikolinakou

Papers

Geomechanical modeling of stresses adjacent to salt bodies: Part 1—Uncoupled models

Modeling stress evolution around a rising salt diapir

Geomechanical modeling of stresses adjacent to salt bodies: Part 2—Poroelastoplasticity and coupled overpressures

Prediction and interpretation of the performance of a deep excavation in Berlin sand

Comparison of evolutionary and static modeling of stresses around a salt diapir