Abstract
The sealing of a fault zone has been a focus for geological studies in the past decades. The majority of previous studies have focused on the extensional regimes, where the displacement pressure difference between fault rock and reservoir was used to evaluate the fault-sealing property from the basic principle of fault sealing. When considering the displacement pressure difference, the impact of gravity on the fault rock was considered, whereas the impact of horizontal stress was ignored. In this study, we utilize the displacement pressure difference as an index to evaluate the sealing capacity of strike-slip faults, in which both the impacts of gravity and horizontal stress on the fault rocks are all integrated. By calculating the values of σH/σV and σh/σV in the vicinity of fault planes, the coefficient K of compaction impacts on fault rocks between normal stress to fault planes and gravity was then determined. By revealing the quantitative relationship between the displacement pressure of rocks, burial depth and clay content, the displacement pressure difference between fault rocks and reservoirs were calculated. The results suggest that the sealing capacity of a strike-slip fault is not only related to the magnitude of normal stress to the fault plane, but also to the stress regime. The clay content is also an important factor controlling the sealing capacity of strike-slip faults.
Highlights
In the process of subsurface oil and gas migration and accumulation, faults can be barriers to hydrocarbon accumulation [1,2,3,4,5,6]
As the clay of fault rocks derives from the strata of both the hanging wall and the footwall, the clay content of a fault zone is highly related to both fault throw and clay contents of stratigraphy in two walls
By comparing the displacement pressures of fault rock and reservoir rock, we found that the disrange of reverse fault stress regime is greater than that of Pd(f − r) within the depth range of strike-slip fault stress regime (Figure 8c,d)
Summary
In the process of subsurface oil and gas migration and accumulation, faults can be barriers to hydrocarbon accumulation [1,2,3,4,5,6]. Several algorithms have been proposed to evaluate the fault sealing properties quantitatively, either based on the continuity of clay smears or average clay content within the fault zones, e.g., Clay Smear Potential (CSP) [17,18], Shale Smear Factor (SSF) [19], Shale Gouge Ratio (SGR) [20] and Scaled Shale Gouge Ratio (SSGR) [21]. These algorithms evaluate the fault sealing properties by considering the re-distribution of mudstone/shale beds or the clay/content of the beds in sheared fractures
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