A Comparison Of Leak-Off Test And Extended Leak-Off Test Data For Stress Estimation

Addis, M.A.; Hanssen, T.H.; Yassir, Najwa; Willoughby, D.R.; Enever, J.R.

doi:10.2118/47235-ms

Cited by 32 publications

(18 citation statements)

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“…In the fault core (test 4), the flow rate significantly increased to a maximum value of 2.8 L/min when the pressure was set above 3.4 MPa ( t = 3.85 h). Injections conducted in test 2, in the intact host rock, followed an extended leak‐off test protocol [ Addis et al , ]. The first failure in the host rock was observed for a pressure of about 4.4 MPa (formation breakdown pressure, FBP; t = 0.74 h).…”

Section: Hydromechanical Response Of the Tested Zonesmentioning

confidence: 99%

Fault structure, stress, or pressure control of the seismicity in shale? Insights from a controlled experiment of fluid‐induced fault reactivation

Barros

Daniel²,

Guglielmi

et al. 2016

JGR Solid Earth

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Clay formations are present in reservoirs and earthquake faults, but questions remain on their mechanical behavior, as they can vary from ductile (aseismic) to brittle (seismic). An experiment, at a scale of 10 m, aims to reactivate a natural fault by fluid pressure in shale materials. The injection area was surrounded by a dense monitoring network comprising pressure, deformation, and seismicity sensors, in a well‐characterized geological setting. Thirty‐two microseismic events were recorded during several injection phases in five different locations within the fault zone. Their computed magnitude ranged between −4.3 and −3.7. Their spatiotemporal distribution, compared with the measured displacement at the injection points, shows that most of the deformation induced by the injection is aseismic. Whether the seismicity is controlled by the fault architecture, mineralogy of fracture filling, fluid, and/or stress state is then discussed. The fault damage zone architecture and mineralogy are of crucial importance, as seismic slip mainly localizes on the sealed‐with‐calcite fractures which predominate in the fault damage zone. As no seismicity is observed in the close vicinity of the injection areas, the presence of fluid seems to prevent seismic slips. The fault core acts as an impermeable hydraulic barrier that favors fluid confinement and pressurization. Therefore, the seismic behavior seems to be strongly sensitive to the structural heterogeneity (including permeability) of the fault zone, which leads to a heterogeneous stress response to the pressurized volume.

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Section: Hydromechanical Response Of the Tested Zonesmentioning

confidence: 99%

Fault structure, stress, or pressure control of the seismicity in shale? Insights from a controlled experiment of fluid‐induced fault reactivation

Barros

Daniel²,

Guglielmi

et al. 2016

JGR Solid Earth

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“…These pumping tests are conducted in short open-hole well sections often beneath cemented casing shoes, principally in order to assess drilling mud densities, however they are also useful for estimating the magnitude of the least principal stress. In regional compilations of in situ stress data, LOT data are plotted relative to depth, and a lower bound provides a reasonable estimate of the magnitude of the least principal stress (Breckels & van Eekelen 1982;Addis et al 1998). The magnitude of SHmax is generally the most difficult parameter to constrain.…”

Section: Methodsmentioning

confidence: 99%

“…It is assumed that the notation on the company records follows this convention, so that LOTs are taken to fracture whereas FITs are not, however it is not possible to verify this without consulting the raw data which are not available. Hydraulic fracture tests and extended leak-off tests (XLOTs or ELOTs) provide improved estimates of the least principal stress magnitude (Addis et al 1998;White et al 2002), however no such data were available to this study. The data are presented in Figure 7, and suggest that the leak-off pressure commonly exceeds the magnitude of the vertical stress.…”

Section: Horizontal Stress Magnitudesmentioning

confidence: 99%

Impact of in situ stress and fault reactivation on seal integrity in the East Irish Sea Basin, UK

Williams

Gent

Fellgett

et al. 2018

Marine and Petroleum Geology

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Despite having been affected by several stages of exhumation during the Cretaceous and Cenozoic, the contemporary stress state of the East Irish Sea (EISB) is poorly characterised. As the basin is mature in terms of exploitation of hydrocarbons, future exploration beyond the conventional Sherwood Sandstone Group reservoir (Triassic) necessitates a greater understanding of the in situ stress field, while proposed natural gas storage and carbon sequestration schemes also require detailed stress field information. Using petroleum well data, the in situ stress field of the EISB has been characterised to assess the mechanical seal integrity. A strike-slip stress regime most-likely prevails in the basin, meaning the Maximum Horizontal Stress (SHmax) is the greatest of the principal stresses. Interpretation of stress orientation data suggests that SHmax is oriented 152˚ ± 12˚, consistent with mean stress orientations across the wider region associated with plate boundary forces. Some degree of structural control appears to influence the orientation of SHmax, with orientations locally aligned sub-parallel to major Permo-Triassic basin-bounding faults. Fault reactivation risk is evaluated through modelling the pore pressure increase required to induce failure on pre-existing faults. Vertical faults striking 30˚ from SHmax are optimally-oriented to become reactivated under elevated pore pressure conditions. For any project relying on an element of fault seal for the containment of buoyant fluids at the average reservoir depth of 800 m, pore pressure increase should be less than 3.3 MPa to avoid reactivating pre-existing optimally-oriented faults. Higher pressure increases would be required to initiate reactivation of faults with other orientations. Vertical faults striking perpendicular to SHmax are least likely to become reactivated, and in the absence of halite, seal integrity would instead be limited by caprock strength and capillary-entry pressure. Major faults affecting the basin have been analysed for their slip tendency (ratio of shear to normal stress), which provides an indication of their susceptibility to become reactivated. Although the analysis is limited due to lack of an accurate 3D representation of the fault network, the results suggest that many of the fault orientations observed in the EISB exhibit high slip tendencies, including N-S striking faults to the north and west of the East Deemster Fault, where the SHmax orientation is NW-SE. Faults striking perpendicular to SHmax, such as the Lagman Fault, are least likely to become reactivated due to higher normal stresses that inhibit frictional sliding, while faults striking parallel or very close to SHmax also exhibit low slip tendency as they are not subjected to significant shear stresses.

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“…Some further data on the S hmin magnitude can be derived from borehole tests that are often conducted by default to test borehole stability. During a Leak-Off Test (LOT), the fluid pressure is increased in the borehole until the fluid leaks into the formation (Bell 1996;Addis et al 1998). The fluid pressure at which the leak-off occurred is used as a proxy for the S hmin magnitude, even though it is not as reliable as an HF test.…”

Section: In Situ Stress Statementioning

confidence: 99%

The 3D stress state from geomechanical–numerical modelling and its uncertainties: a case study in the Bavarian Molasse Basin

Ziegler

Heidbach

2020

Geotherm Energy

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Knowledge of the undisturbed stress state is a key parameter for borehole stability, productivity and induced seismicity hazard assessment. Due to the sparse and incomplete availability of data records, 3D geomechanical–numerical modelling is applied to estimate the stress state in a volume. To assess the quality of the model results, the model uncertainties have to be quantified. We present an approach that provides the uncertainties of the six independent stress tensor components at each location in the model volume by an average value and its standard deviation. We explore the uncertainties introduced to the model results with respect to the stress magnitude data used for model calibration. We test our approach on a model of the Bavarian Molasse Basin which includes the area around Munich with many geothermal projects. In the test area, we find large uncertainties in the modelled magnitude of the maximum horizontal stress ($$\text{S}_\text {Hmax}$$SHmax) in the order of 15–30%. The uncertainties in the magnitude of the minimum horizontal stress ($$\text{S}_\text {hmin}$$Shmin) are smaller between 5 and 20%. In connection with an adequate failure criterion, we compare our model results to the seismological observations at two neighbouring geothermal projects. Whilst Aschheim/Feldkirchen/Kirchheim remained seismically quiet, induced seismicity was recorded in Poing. Our modelled undisturbed stress state was confirmed by these observations by showing in average a stable stress state in Aschheim/Feldkirchen/Kirchheim and a critical stress state in Poing. If the uncertainties in terms of two standard deviations are considered, this does not change. This demonstrates the increase in model significance when uncertainties are available.

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A Comparison Of Leak-Off Test And Extended Leak-Off Test Data For Stress Estimation

Cited by 32 publications

References 0 publications

Fault structure, stress, or pressure control of the seismicity in shale? Insights from a controlled experiment of fluid‐induced fault reactivation

Fault structure, stress, or pressure control of the seismicity in shale? Insights from a controlled experiment of fluid‐induced fault reactivation

Impact of in situ stress and fault reactivation on seal integrity in the East Irish Sea Basin, UK

The 3D stress state from geomechanical–numerical modelling and its uncertainties: a case study in the Bavarian Molasse Basin

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