Quantitative evaluation of synsedimentary fault opening and sealing properties using hydrocarbon connection probability assessment

Abstract

Hydraulic behaviors of faults in sedimentary basins have been paid close attention in studies of hydrocarbon migration and accumulation because of their important functions in basin hydraulic circulations. In previous studies, however, the function of faults in hydrocarbon migration is characterized by the sealing capacity of faults. In fact, sealing is only an impressive and time-dependent aspect of the hydraulic behavior of faults, which may act as seals during some periods and as pathways some time later. Therefore, in hydrocarbon migration studies, sealing indices may successfully be used in some cases but not in others. In this article, we introduce an empirical method (termed the fault-connectivity probability method) for assessing the hydraulic connecting capacity of a fault for hydrocarbon migration over geological time scales. The method is based on the recognition that observable hydrocarbon in reservoirs should result from the opening and closing behavior of the fault during the entire process of hydrocarbon migration. In practice, the cumulative petroleum migration through a segment of the fault zone is identified by the presence (or not) of hydrocarbon-bearing layers on both sides of the segment. Data from the Chengbei step-fault zone (CSFZ) in the Qikou depression, Bohai Bay Basin, northeast China, were used

Geometry, kinematics and dynamic characteristics of a compound transfer zone: the Dongying anticline, Bohai Bay Basin, eastern China

“…Previous studies have found that a higher SGR indicates a poorer porosity and permeability in the fault damage zone, and the fault will have good sealing ability when the shale content of the fault zone exceeds 0.7 in the Dongying Depression [34,36].…”

“…In this paper, the Shale Gouge Ratio (SGR) and the stress normal to the fault plane (δ) were used to characterize fault sealing properties [33]. Clay or shale smeared into the fault zone has been considered an effective factor impacting the sealing ability of the fault [34]. In this paper, SGR is used to estimate the amount of muddy fault smear, which is defined as the ratio between the throw of the fault and the total thickness of mudstones within the throw [34].…”

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

“…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.…”