Coastal & Marine Geology Program > Center for Coastal Studies > Subsidence and Fault Activation Project

Subsidence and Fault Activation Related to Fluid Energy Production, Gulf Coast Basin Project

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Introduction:

Project Overview

Investigators

Research Objectives:

Production Parameters

Reservoir Parameters

Framework

Ground Characterization

Geophysical Methods

Land Loss

Publications

Project Contact:

Bob Morton

Task 3: Investigate Depositional and Structural Framework of Selected Fields and Evaluate Mechanisms of Subsidence and Fault Activation
Objectives
This task will evaluate how regional stratigraphy and structure may influence subsidence and fault activation potential. Both field areas where subsidence has and has not been detected will be examined. Task objectives are:

Determine how stratigraphy and structure influence subsidence and fault activation potential by:

Investigating the effects of facies architecture and structural style on subsidence and faulting susceptibility;
Examining the three-dimensional distribution of reservoirs and their relationship to surficial subsidence patterns;

Investigate the physical processes by which subsurface changes in pore pressure and fluid movement are translated into surface subsidence;
Examine stress-strain relationships in unconsolidated and semiconsoldated rocks that experience recurrent failure
Evaluate effects of reservoir management schemes on subsidence and faulting;
Quantify the processes associated with subsidence so models and predictions can be applied to other fields.

Methods
Sandstones have much lower compressibilities than mudstones because mudstones typically contain large volumes of water that are released through normal compaction and hydration processes. These natural diagenetic processes can be accelerated or altered as a result of subsurface fluid production. Therefore, it is important to know the depths of production, number and stacking arrangement of multiple reservoirs, sand-shale ratios of producing intervals, and sand- shale ratios of the overburden around fields where subsidence has occurred. The number and spacing of faults and their relationship to salt domes or shale ridges may also influence the potential for either promoting or preventing induced subsidence.

Little information has been published on the state of stress (confining pressures and axial loads) around fields where subsidence has occurred. Differential pressures across fault planes, directions of subsurface fluid motion around faults, rock compressibilities, and other properties that might control slippage along faults can be mapped and measured using available subsurface data such as pressure tests and production records. Previously determined creep of Gulf Coast sediments would provide a basis for estimating reservoir compaction coefficients and thus the potential for subsidence of other fields. A cooperative with Stanford University will provide the geomechanics expertise needed to understand the links between reservoir compaction and fault activation. Results of this task eventually will be integrated with results from other tasks (production characteristics and subsidence mechanisms) in order to develop adequate environmental impact models of induced subsidence and land losses.

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