Experimental study on clay gouge evolution in mechanically stratified sequences
Creators: name: Schmatz, Joyce
Publisher: name: RWTH Aachen University
Year: 2011
Subjects: subject: 550
subject: Abschiebung
subject: Particle-Image-Velocimetry
subject: Geowissenschaften
subject: clay smear
subject: normal fault
subject: sandbox experiment
subject: PIV
subject: Shale Gouge Ratio

description: Aachen, Techn. Hochsch., Diplomarbeit, 2006; Aachen : Publikationsserver der RWTH Aachen University (2011). = Aachen, Techn. Hochsch., Diplomarbeit, 2006
description: Normal faults play an important role in hydrocarbon exploration. A normal fault can act as a migration path for fluids or seal fluids compartments. Sealing is enhanced when the fault zones are filled with impermeable materials like clay. “Clay smear is a loosely defined term born in hydrocarbon geology; its usage differs between publications, and the definition of processes operating is often unclear. In most general meaning, the term includes all processes, which somehow transform clay in the wall rock into clay that is part of the fault zone. Processes included are clay abrasion, shear in releasing fault links, preferred smear and lateral clay injection” (van der Zee et al., 2003). This study focuses on experimental investigations on the generation of sealed faults. The sealing quality of the fault is set in context to the rheological properties of the host rock. Structural and mechanical features such as shear strength of the materials involved, clay smear, the evolution of releasing bends and fault lenses play an important role and are investigated using analogue sandbox experiments. The experimental results are compared intensively with scientific theories and previous studies dealing with similar topics in the following chapters. The aim of this study is to find out which parameters have major effect on the final gouge geometry and composition and to investigate the kinematical evolution. Finally, the experimental results should give us information on the validity of in hydrocarbon geology frequently used fault sealing prediction theories and methods. The application of analogue models is a useful method to investigate the effect of different boundary conditions and material properties on the evolution of a fault zone. Dry sand or wet clay have been used before, but a combination of the two was not possible, and instead model materials such as silicon were used. But, the closer the model approaches to scaled analogues of natural conditions, the more informative are the experimental results. So, why not build up a model that includes real sand and clay instead of analogue model materials? For this purpose an analogue sandbox-model was built. Experiments are run under completely water-saturated conditions to simulate the behavior of ‘wet’ clay and to enable the investigation of fault development in layered sand-clay sequences. The observations focus on the behavior of the clay layers, as they have strong influence on the permeability, which is important in terms of hydrogeology and for the petroleum industry. This sandbox makes it possible to carry out experiments in the dimension of 20x40x20 cm. The rigid basement fault dips with 70° and the velocity can be varied from 2 up to 12 cm/hr with a maximum offset of 60 mm. In nine experiment series parameters such as the clay’s rigidity or the number of clay layers were varied systematically. These variations lead to the evolution of different gouge structures that strongly deviate in their structure and transport properties. The experimental results are discussed in reference to their natural effect on the fault zone structure. 2D-images of the sandbox experiments were additionally processed with PIV-software (Particle Image Velocimetry) to quantify the displacement field. The software calculates the motion at the scale of a sand grain. The results give useful information on fault zone evolution. Results are investigated in terms of fault statistics and fault geometry. To infer the mechanisms of fault zone evolution in both nature and analogue models I focus on the mechanical background and kinematics of the initial deformation phase.
description: Published by Publikationsserver der RWTH Aachen University, Aachen