Evaluation of geological factors in characterizing fault connectivity during hydrocarbon migration: Application to the Bohai Bay Basin
Highlights
► In this study we evaluate if a fault may serve as a conduit for oil migration. ► Geoparameters pertinent to a fault are assessed for characterizing fault sealing. ► Accumulated oils are used as indicators to deduce hydraulic connectivity of a fault. ► A concept of fault-connectivity probability offers a conduit for statistical analyses.
Introduction
Faults play an important role in hydrocarbon migration and accumulation (Smith, 1966, Smith, 1980, Berg, 1975, Weber et al., 1978, Galloway et al., 1982, Hooper, 1991, Knipe, 1992, Fisher and Knipe, 1998, Fisher and Knipe, 2001), because they can act as conduits or barriers (Sample et al., 1993, Boles and Grivetti, 2000, Eichhubl and Boles, 2000, Boles et al., 2004, Jin et al., 2008) during fluid migration. The dual behavior has been the focus of discussions over several decades (Sibson, 1981, Sibson, 1994, Losh et al., 1999). Nevertheless, the role of faults in hydrocarbon migration still needs to be better understood.
Previous researchers (Sibson et al., 1975, Hooper, 1991, Moretti, 1998) suggested that local high-permeability segments of a fault serve as flow paths when faulting is active, but as barriers when faulting is inactive. Faulting is a complex process: two walls move relatively in opposite directions and are offset, resulting in some open segments that permit fluid flow (Haney et al., 2005). In fact, a fault plane is generally a zone with complex internal structures, containing possibly subsidiary faults, fractures, fault gouge and breccias, and cataclasites (Chester and Logan, 1986, Smith et al., 1990, Forster and Evans, 1991, Chester et al., 1993, Bruhn et al., 1994, Caine et al., 1996). These internal elements may display different petrophysical and hydraulic properties at different locations and vary with variable geological conditions during basin evolution (Caillet and Batiot, 2003). For example, following a climax tectonic event, the stress which once generated or moved a given fault is probably relaxing so that the fault zone tends to close, and/or the once open zone tends to be gradually cementated (healed) in the ensuing period of quiescence.
The episodic opening and closing of a fault segment can be viewed as a series of complex switches in the history of a basin, which characterize the hydraulic behaviors of a fault (e.g., Sibson et al., 1975, Losh et al., 1999, Xie et al., 2001, Jin et al., 2008). The distribution of these switches on a fault plane and fluxes of fluid channeling through the switches, which depend on the aperture of an open fault, are highly variable because geological factors affecting the sealing characteristics of fault zones are numerous and complex (Hasegawa et al., 2005). Specifically, the amount of fluid flow through an open fault segment during each faulting event is variable (Haney et al., 2005)
In most cases, the duration of an active faulting episode is only a fraction of the total life span, of the fault and is even lesser compared to the duration of the entire migration process (Hooper, 1991, Roberts and Nunn, 1995). As a result, only a small amount of hydrocarbons migrated through a fault segment during one episode of faulting (Haney et al., 2005); and probably thousands upon thousands of faulting episodes and associated migration events are needed to accumulate a commercial quantity of hydrocarbons in a trap (Anderson et al., 1994). The properties of an open fault segment are probably ever-changing and fluid flows during individual migration events behave differently. Fault “opening” and associated hydrocarbon migration are geological processes, representing a series of different physical processes that occurred repeatedly over a geological time span. Any permeability measurements at different localities along a fault zone would only represent the current state of fault sealability, which may differ greatly from that during active faulting and hydrocarbon migration.
Many studies have been devoted to identifying diagnostic parameters that may be universally applied to effective assessing the sealability of faults (e.g., Schowalter, 1979, Watts, 1987, Harding and Tuminas, 1989, Bouvier et al., 1989, Lindsay et al., 1993, Knott, 1993, Yielding et al., 1997, Sorkhabi et al., 2002, Sorkhabi and Tsuji, 2005). Dozens of parameters have been used for evaluating sealability of faults (Bouvier et al., 1989, Lindsay et al., 1993, Knott, 1993, Yielding et al., 1997, Sorkhabi et al., 2002). In fact, any one factor that affects sealability in one or other aspects can be parameterized. However, the effectiveness of a particular parameter varies from case to case (Færseth et al., 2007). The role of a geological factor on fault sealability during hydrocarbon migration must be well understood before the factor can be accurately parameterized and effective.
Zhang et al. (2010) introduced an empirical fault-connectivity probability method to assess the hydraulic connectivity of faults during hydrocarbon migration at a geological time scale. Whether the petroleum migration has already occurred through a fault segment at any point of time in the basin history or not is identified by the presence or absence of hydrocarbon-bearing layers on both sides of the segment. Data from the Chengbei Step-Fault Area (CSFA) in the Qikou Depression, Bohai Bay Basin, northeast China, were used to develop this method. The role of an open fault segment in migration was then assessed by the relationship between the fault-connectivity probability and a parameter called the fault opening index (Zhang et al., 2010).
The hydraulic-connectivity probability concept of Zhang et al. (2010) offers a practically statistical approach to characterize the opening and closing of a fault segment during hydrocarbon migration. Furthermore, it may be used to assess the effectiveness of a parameter that represents the role of one or several geological factors in hydrocarbon migration through a fault. This study is an effort to assess the effectiveness of parameters used in characterizing fault behaviors during hydrocarbon migration, and to compare the effectiveness of various parameters when applied in the CSFA.
Section snippets
Parameters characterizing fault connectivity
Many parameters that represent geological factors affecting fault connectivity have been proposed to evaluate whether a fault would have served as a barrier or conduit for hydrocarbon migration (e.g., Harding and Tuminas, 1989, Knott, 1993, Knipe et al., 1997, Sorkhabi et al., 2002, Færseth et al., 2007). Some parameters that can be obtained from routine exploration data are discussed below (Fig. 1):
Parameterization of geological factors controlling fault connectivity
In this paper, data from the CSFA are used to establish a method to assess this effect.
Effectiveness of parameters in assessing fault connectivity
Hydrocarbon migration through a fault occurred within the entire fault zone, which can be viewed as a distinct geologic entity, during a geological period and are controlled by a suite of complex geological processes. The concept of fault-connectivity probability is therefore introduced to characterize the composite effect of geological processes in fault-related hydrocarbon migration (Zhang et al., 2010).
Discussions and conclusions
The role of faults in hydrocarbon migration, although generally acknowledged (Smith, 1966, Smith, 1980, Berg, 1975, Knipe, 1992, Fisher and Knipe, 1998, Fisher and Knipe, 2001), is rather difficult to be assessed. Considering the multitude of geological factors and processes affecting fault activities and fluid flow, the principal problems lie in the definition of valid parameters to be used to evaluate the controls on fault connectivity during hydrocarbon migration over a long geologic period.
Acknowledgment
This study was supported by the Chinese National Natural Science Foundation (40902041) and Chinese National Major Fundamental Research Developing Project (2011CB201105). Qianjin Liao, Shuqin Yuan, and Junqing Su of Dagang Oil Company are acknowledged for providing basic data and helpful discussion. We thank Beicip-Franlab for providing the Temis3D software used in our pressure modeling. We appreciate the comments and encouragement from Y. F. Wang, the reviewers Dr. Leonardo Duerto and Dr.
References (80)
- et al.
Analysis of faulting in porous sandstones
Journal of Structural Geology
(1983) - et al.
Calcite cementation along the Refugio/Carneros fault, coastal California. A link between deformation, fluid movement and fluid-rock interaction at a basin margin
Journal of Geochemical Exploration
(2000) - et al.
Complexity in fault zone structure and implications for fault seal prediction
Thickness-displacement relationships for fault zones
Journal of Structural Geology
(1990)- et al.
The permeability of faults within siliciclastic petroleum reservoirs of the North Sea and Norwegian continental shelf
Marine and Petroleum Geology
(2001) - et al.
Quantitative fault seal prediction- a case study from Oseberg Syd
- et al.
Fault seal processes: systematic analysis of fault seals over geological and production time scales
Thickness-displacement relationships for deformation zones
Journal of Structural Geology
(1988)Faulting processes and fault seal
- et al.
The emplacement of clay smears in syn-sedimentary normal faults. inference from field observations near Frechen, Germany
Episodic fluid expulsion from geopressured sediments
Marine and Petroleum Geology
Empirical estimation of fault rock properties
Theoretical aspects of cap-rock and fault seals for single- and two-phase hydrocarbon columns
Marine and Petroleum Geology
Evidence for episodic expulsion of hot fluids along faults near diapiric structures of the Yinggehai Basin, South China Sea
Marine and Petroleum Geology
Shale gouge ratio calibration by geohistory
Gulf of Mexico growth fault drilled, seen as oil, gas migration pathway
Oil & Gas Journal
Fluid flow along potentially active faults in crystalline rock
Geology
Capillary pressure in stratigraphic traps
AAPG Bulletin
Evolution of a hydrocarbon migration pathway along basin bounding faults. Evidence from fault cement
AAPG Bulletin
Three-dimensional seismic interpretation and fault sealing investigations, Nun river field, Nigeria
AAPG Bulletin
Using calibrated shale gouge ratio to estimate hydrocarbon column heights
AAPG Bulletin
Fracturing and hydrothermal alteration in normal fault zones
Pure and Applied Geophysics
2D modeling of hydrocarbon migration along and across growth faults. an example from Nigeria
Petroleum Geoscience
Fault zone architecture and permeability structure
Geology
Implications for mechanical properties of brittle faults from bservations of the Punchbowl fault zone, California
Pure and Applied Geophysics
Internal structure and weakening mechanisms of the San Andreas fault
Journal of Geophysical Research
Rates of fluid flow in fault systems – Evidence for episodic rapid fluid flow in the Miocene Monterey formation, coastal California
American Journal of Science
Methodology for risking fault seal capacity: implications of fault zone architecture
AAPG Bulletin
Fault sealing processes in siliciclastic sediments
Hydrogeology of thrust faults and crystalline thrust sheets. Results of combined field and modeling studies
Geophysical Research Letters
Depositional Framework, Hydrostratigraphy, and Uranium Mineralization of the Oakville Sandstone (Miocene), Texas coastal plain
Fault-zone seals in siliciclastic strata of the Columbus Basin, offshore Trinidad
AAPG Bulletin
A moving fluid pulse in a fault zone
Nature
Structural interpretation of hydrocarbon traps sealed by basement normal blocks and at stable flank of foredeep basins and at rift basins
AAPG Bulletin
Fault seal analysis: reducing our dependence on empiricism
Fault-seal analysis in the Temana field, offshore Sarawak, Malaysia
Uncertainties associated with fault sealing analysis
Petroleum Geoscience
The effect of temperature on sealing capacity of faults in sandstone reservoirs: examples from the Gullfaks and Gullfaks Sør fields, North Sea
AAPG Bulletin
Fluid migration along growth faults in compacting sediments
Journal of Petroleum Geology
Role of fluid pressure in mechanics of overthrust faulting
Bulletin of the Geological Society of America
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