Fault seal calibration: a brief review

Abstract

Calibration is a necessary step in the workflow for prediction of fault seal because there is no direct way to detect the hydraulic behaviour of a fault at the scale of a hydrocarbon trap. Over the last 20 years two general approaches have been developed: Measurement of hydraulic properties of fault-zone samples (lab calibration), then mapping these results onto the appropriate parts of trap-bounding faults.Design of simple algorithms which attempt to capture a salient feature of the fault zone (e.g. CSP, SSF, SGR), then looking at known trap-bounding faults to find a relationship between the algorithm and the presence or capacity of a seal (sub-surface calibration).Seal capacity is typically described by Hg–air threshold pressure in the lab or static pressure differences in the subsurface (e.g. hydrocarbon buoyancy pressure). In addition to likely interpretation and geometry errors in approaches (i) and (ii), further uncertainty is introduced when converting the calibrated seal strength to potential hydrocarbon column height, because of the variability of subsurface hydrocarbon fluids (interfacial tension). Despite these potential problems, the different methodologies typically agree reasonably well in their predictions for fault-seal capacity. However, this agreement may be largely coincidental and is likely to be a response to the heterogeneity of fault-zone structure (especially at intermediate ‘compositions’ or SGR).

Role of Faults in Hydrocarbon Leakage in the Hammerfest Basin, SW Barents Sea: Insights from Seismic Data and Numerical Modelling

“…Fault reactivation and slip could have resulted from elevated pore pressures due to the increase of the hydrocarbon column height during gas expansion, oscillations in pressure due to ice loading-unloading and the overall fault orientation to the maximum horizontal stress field, S Hmax [13,72,73] and the characteristics of fault damage zones [63,74]. Additionally, gas cap expansion due to overburden removal by erosion would contribute to elevated pressures [11,75], enhancing the likelihood of fault slip and increase in permeability.…”

Induced seismicity within geological carbon sequestration projects: Maximum earthquake magnitude and leakage potential from undetected faults

“…Different methodologies are also used for predicting fault sealing potential within sandstone/shale sequences (e.g., Bouvier et al, 1989;Antonellini and Aydin, 1994). One such methodology is based on the Shale Gouge Ratio (SGR; Yielding et al, 2010). This methodology uses the average clay content of the layers that have slipped past each other on the opposite side of a fault in order to evaluate fault-gouge composition (Fig.…”

From mechanical modeling to seismic imaging of faults: A synthetic workflow to study the impact of faults on seismic

“…Strictly speaking, fault sealing as a property over the fault volume cannot be mapped directly with seismic. One rather looks at the impact of the fault on the surrounding rock (e.g., across fault pressure differences) to infer something about the fault properties and its sealing capacity (Yielding et al, 2010). A single fault surface with fault sealing properties determined in this manner is a reasonable estimate of the flow properties across and along the fault.…”