Elsevier

Marine and Petroleum Geology

Volume 28, Issue 9, September 2011, Pages 1634-1647
Marine and Petroleum Geology

Evaluation of geological factors in characterizing fault connectivity during hydrocarbon migration: Application to the Bohai Bay Basin

https://doi.org/10.1016/j.marpetgeo.2011.06.008Get rights and content

Abstract

Faults play an intricate role in hydrocarbon migration and accumulation since they can serve either as a conduit or a seal. Quantitative evaluation of fault opening/sealing properties requires the selection of valid and optimal parameters among numerous geological factors to characterize the hydraulic behaviors of faults. The present study focuses on the Chengbei Step-Fault Area in the Qikou Depression, Bohai Bay Basin, NE China, because hydrocarbon migration and accumulation in this area occurred in a relatively short period so that accumulated hydrocarbons can be used as an indicator to deduce hydraulic connectivity of a fault zone between two sites. Various geological parameters pertinent to a fault, such as burial depth, dip angle, throw, strike, percentage of sandstone of faulted intervals, fluid pressure in faulted mudstone, stress normal to the fault plane, and shale gouge ratio, are analyzed to assess their effectiveness in characterizing fault connectivity. An index, the fault-connectivity probability (Np), is proposed to evaluate the possibility that a fault has been once serving as a migration pathway. The statistical relationship between Np and any a geological parameter may be used to indicate the effectiveness of this parameter in characterizing the connectivity of a fault during hydrocarbon migration. The correlation coefficient of a relationship is a good indicator of the effectiveness; and the results are generally in agreement with qualitative assessments. Parameters representing a single geological factor are generally ineffective, whereas those representing implicitly or explicitly two or more factors, such as shale gouge ratio, stress normal to the fault plane, and fault opening index, are more effective.

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)

  • S.J. Roberts et al.

    Episodic fluid expulsion from geopressured sediments

    Marine and Petroleum Geology

    (1995)
  • S. Sperrevik et al.

    Empirical estimation of fault rock properties

  • N. Watts

    Theoretical aspects of cap-rock and fault seals for single- and two-phase hydrocarbon columns

    Marine and Petroleum Geology

    (1987)
  • X.N. Xie et al.

    Evidence for episodic expulsion of hot fluids along faults near diapiric structures of the Yinggehai Basin, South China Sea

    Marine and Petroleum Geology

    (2001)
  • G. Yielding

    Shale gouge ratio calibration by geohistory

  • R. Anderson et al.

    Gulf of Mexico growth fault drilled, seen as oil, gas migration pathway

    Oil & Gas Journal

    (1994)
  • C.A. Barton et al.

    Fluid flow along potentially active faults in crystalline rock

    Geology

    (1995)
  • P.R. Berg

    Capillary pressure in stratigraphic traps

    AAPG Bulletin

    (1975)
  • J.R. Boles et al.

    Evolution of a hydrocarbon migration pathway along basin bounding faults. Evidence from fault cement

    AAPG Bulletin

    (2004)
  • J.D. Bouvier et al.

    Three-dimensional seismic interpretation and fault sealing investigations, Nun river field, Nigeria

    AAPG Bulletin

    (1989)
  • P. Bretan et al.

    Using calibrated shale gouge ratio to estimate hydrocarbon column heights

    AAPG Bulletin

    (2003)
  • R.L. Bruhn et al.

    Fracturing and hydrothermal alteration in normal fault zones

    Pure and Applied Geophysics

    (1994)
  • G. Caillet et al.

    2D modeling of hydrocarbon migration along and across growth faults. an example from Nigeria

    Petroleum Geoscience

    (2003)
  • J.S. Caine et al.

    Fault zone architecture and permeability structure

    Geology

    (1996)
  • F.M. Chester et al.

    Implications for mechanical properties of brittle faults from bservations of the Punchbowl fault zone, California

    Pure and Applied Geophysics

    (1986)
  • F.M. Chester et al.

    Internal structure and weakening mechanisms of the San Andreas fault

    Journal of Geophysical Research

    (1993)
  • P. Eichhubl et al.

    Rates of fluid flow in fault systems – Evidence for episodic rapid fluid flow in the Miocene Monterey formation, coastal California

    American Journal of Science

    (2000)
  • R.B. Færseth et al.

    Methodology for risking fault seal capacity: implications of fault zone architecture

    AAPG Bulletin

    (2007)
  • Q.J. Fisher et al.

    Fault sealing processes in siliciclastic sediments

  • C.B. Forster et al.

    Hydrogeology of thrust faults and crystalline thrust sheets. Results of combined field and modeling studies

    Geophysical Research Letters

    (1991)
  • W. Galloway et al.

    Depositional Framework, Hydrostratigraphy, and Uranium Mineralization of the Oakville Sandstone (Miocene), Texas coastal plain

    (1982)
  • R.G. Gibson

    Fault-zone seals in siliciclastic strata of the Columbus Basin, offshore Trinidad

    AAPG Bulletin

    (1994)
  • M.M. Haney et al.

    A moving fluid pulse in a fault zone

    Nature

    (2005)
  • T.P. Harding et al.

    Structural interpretation of hydrocarbon traps sealed by basement normal blocks and at stable flank of foredeep basins and at rift basins

    AAPG Bulletin

    (1989)
  • T.R. Harper et al.

    Fault seal analysis: reducing our dependence on empiricism

  • S. Hasegawa et al.

    Fault-seal analysis in the Temana field, offshore Sarawak, Malaysia

  • J. Hesthammer et al.

    Uncertainties associated with fault sealing analysis

    Petroleum Geoscience

    (2000)
  • J. Hesthammer et al.

    The effect of temperature on sealing capacity of faults in sandstone reservoirs: examples from the Gullfaks and Gullfaks Sør fields, North Sea

    AAPG Bulletin

    (2002)
  • E.C.D. Hooper

    Fluid migration along growth faults in compacting sediments

    Journal of Petroleum Geology

    (1991)
  • M.K. Hubbert et al.

    Role of fluid pressure in mechanics of overthrust faulting

    Bulletin of the Geological Society of America

    (1959)
  • Cited by (39)

    • Normal fault transmissibility characteristics under the transition condition of fault conduction and sealing observed in simulation experiments

      2022, Marine and Petroleum Geology
      Citation Excerpt :

      If the capillary threshold pressure of the fault rock is equal to or larger than that of the reservoir rock on both sides of the fault, the oil migrates laterally and enters the reservoir, and vice versa, hence the proportion of mudstone breccia or clay in the fault zone directly increases the capillary threshold pressure of the fault rock. The other is that various parameters associated with mudstone smear (Vrolijk et al., 2016), including the shale smear factor (SSF) (Lindsay et al., 1993), clay smear potential (CSP) (Bouvier et al., 1989), shale gouge ratio (SGR) (Fristad et al., 1997; Yielding et al., 1997), and fault opening index (Zhang et al., 2011), are used to evaluate the mudstone failure conditions (Zhang et al., 2013). Among these indicators, the factors that majorly affect the degree of capillary failure are the mudstone thickness or content in the fault zone and fault throw.

    • Fault characterization and flow barrier detection using capacitance-resistance model and diagnostic plots

      2022, Journal of Petroleum Science and Engineering
      Citation Excerpt :

      The sealing or non-sealing nature of a fault depends on the time scale and may evolve over time (Aubert et al., 2021; Biryukov and Kuchuk, 2012; Moretti, 1998; Yaxley, 1987), due to possible seismic activities (Keranen et al., 2013), or injection pressurization and induced seismicity (Mosaheb and Zeidouni, 2018; Rutqvist et al., 2007). Besides geological and geophysical based methods of identifying and evaluating faults (Takam Takougang et al., 2019; Wu and Hale, 2016; Zhang et al., 2011), pressure transient tests have also been used extensively for identifying and characterizing faults, based on their sealing ability and physical characteristics (such as distance to the well of interest, dip angle). The sealing ability attempts to quantify the fluid or pressure flow across the fault (Hosseini, 2019; Yaxley, 1987).

    View all citing articles on Scopus
    View full text