Fault seal analysis: Methodology and case studies
- Earth Sciences Limited, Lincolnshire (United Kingdom)
Fault seal can arise from reservoir/non-reservoir juxtaposition or by development of fault rock of high entry-pressure. The methodology for evaluating these possibilities uses detailed seismic mapping and well analysis. A {open_quote}first-order{close_quote} seal analysis involves identifying reservoir juxtaposition areas over the fault surface, using the mapped horizons and a refined reservoir stratigraphy defined by isochores at the fault surface. The {open_quote}second-order{close_quote} phase of the analysis assesses whether the sand-sand contacts are likely to support a pressure difference. We define two lithology-dependent attributes {open_quote}Gouge Ratio{close_quote} and {open_quote}Smear Factor{close_quote}. Gouge Ratio is an estimate of the proportion of fine-grained material entrained into the fault gouge from the wall rocks. Smear Factor methods estimate the profile thickness of a ductile shale drawn along the fault zone during faulting. Both of these parameters vary over the fault surface implying that faults cannot simply be designated {open_quote}sealing{close_quote} or {open_quote}non-sealing{close_quote}. An important step in using these parameters is to calibrate them in areas where across-fault pressure differences are explicitly known from wells on both sides of a fault. Our calibration for a number of datasets shows remarkably consistent results despite their diverse settings (e.g. Brent Province, Niger Delta, Columbus Basin). For example, a Shale Gouge Ratio of c. 20% (volume of shale in the slipped interval) is a typical threshold between minimal across-fault pressure difference and significant seal.
- OSTI ID:
- 425399
- Report Number(s):
- CONF-960527-; TRN: 96:004994-0029
- Resource Relation:
- Conference: Annual convention of the American Association of Petroleum Geologists, Inc. and the Society for Sedimentary Geology: global exploration and geotechnology, San Diego, CA (United States), 19-22 May 1996; Other Information: PBD: 1996; Related Information: Is Part Of 1996 AAPG annual convention. Volume 5; PB: 231 p.
- Country of Publication:
- United States
- Language:
- English
Similar Records
Fault seal analysis: Methodology and case studies
Modern analytical techniques for fault surface seal analysis: A Gulf Coast case history