TRAP INTEGRITY IN THE LAM IN ARIA HIGH-NANCAR TROUGH REGION,TIMOR SEA: PREDICTION OF FAULT SEAL FAILURE USING WELL-CONSTRAINED STRESS TENSORS AND FAULT SURFACES INTERPRETED FROM 3D SEISMIC

2000 ◽  
Vol 40 (1) ◽  
pp. 151 ◽  
Author(s):  
D.A. Castillo ◽  
D.J. Bishop ◽  
I. Donaldson ◽  
D. Kuek ◽  
M. de Ruig ◽  
...  
Keyword(s):  
Horizontal Stress ◽  
Column Height ◽  
3D Seismic ◽  
Stress Regime ◽  
Seal Failure ◽  
Hydrocarbon Traps ◽  
Coulomb Failure ◽  
Timor Sea ◽  
Surrounding Areas ◽  
Drilling Conditions

Drilling in the Laminaria High and Nancar Trough areas has shown that many hydrocarbon traps are underfilled or completely breached. Previous studies have shown that fault-trap integrity is strongly influenced by the state of stress resolved on the reservoir bounding faults, suggesting that careful construction of a geomechanical model may reduce the risk of encountering breached reservoirs in exploration and appraisal wells. The ability of a fault to behave as a seal and support a hydrocarbon column is influenced in part by the principal stress directions and magnitudes, and fault geometry (dip and dip azimuth). If a fault is critically stressed with respect to the present-day stress field, there is a high likelihood that the fault will slip, thereby elevating fault zone permeability that enables hydrocarbons to leak. Leakage could be intermittent depending on the degree and rate of fracture healing, and on the recurrence rate between reactivated slip events.High-resolution wellbore images from over 15 wells have been analysed to construct a well-constrained stress tensor. Constraints are based on geomechanical parameters, along with drilling conditions that are consistent with the style of drilling-induced compressive and tensile wellbore wall failure seen in each of these wells. This regional stress analysis of permits AC/P8, AC/P16 and surrounding areas indicates a non-uniform strike-slip stress regime (SHmax > Sv > Shmin) with the orientation of the maximum principal horizontal stress (SHmax) varying systematically from north to south, similar to that previously reported for the western reaches of ZOCA. On the Laminaria High (AC/P8 and AC/L5), SHmax is 15°N ± 6°. Just south of the Laminaria High, there is a marked transition in the SHmax stress direction to about 63°N ± 6°. Over the Nancar Trough (AC/P16), the orientation is consistently NE-SW.Fault surfaces interpreted from 3D seismic data have been subdivided into discrete segments for the purpose of calculating the shear and normal stresses in order to resolve the Coulomb Failure Function (CFF) on each fault segment. The results have been displayed using 3D visualisation techniques to facilitate interpretation. The magnitude of hydrocarbon accumulation (column height) and leakage (residual column) deduced from well results may be explained in part by the CFF resolved on their respective reservoir-bounding faults. By integrating these stress determination and fault imaging technologies, explorationists and reservoir engineers will gain the ability to use these predictive tools to help quantify the likelihood of encountering a breached reservoir prior to drilling.

Regional Top Seal Capacity Analysis in JS-1 Ridge, Offshore Madura Involving Seal Geometry, Capillary Seal, Hydrofracturing Analysis, and Natural Fracture Modelling

2021 ◽  
Keyword(s):  
Vitrinite Reflectance ◽  
Stable Condition ◽  
Horizontal Stress ◽  
Natural Fracture ◽  
Column Height ◽  
Natural Fractures ◽  
Stress Regime ◽  
Hydrocarbon Reservoir ◽  
North East ◽  
Average Maximum

The Early Miocene reefal carbonate of Kujung-1 is the main hydrocarbon reservoir in JS-1 Ridge Area, North East Java Basin. The varying heights of hydrocarbon columns affect the success rate of exploration in Kujung-1 Formation. The shale of Rancak Unit acts as a regional seal of the Kujung-1 Reservoir. This study aims to understand the character, capacity of seal, and its relationship with hydrocarbon column height, to improve the chances of exploration success. The methodology in this study includes estimation of pore pressures, capillary seals, hydrofracturing seals, seal geometry, and natural fractures modeling. The data used in this study include 41 well, laboratory (Mercury Injection capillary pressure, vitrinite reflectance and X-ray diffraction), and 3D seismic data. The pore pressure of Rancak Unit indicates that it is slightly overpressured by loading mechanism. The presence of slight overpressure increases sealing capacity of Rancak Unit to 1.95 MPa or 221 m gas column equivalent. Hydrofracturing seal does not play an important role in Rancak Unit. The seal geometry of Rancak has good to very good qualitative capabilities to hold hydrocarbon in Kujung-1 Reservoir. Present-day stress magnitudes and orientations have been determined from bore-hole breakout, drilling-induced fractures and LOTs from two wells. Interpretation of borehole breakout and drilling-induced tensile shows that average maximum horizontal stress direction is northeast-southwest. The geomechanically model shows that predominant stress regime at KD-1 and KD-3 Wells is normal stressregime. Fracture distribution based on natural fracture modeling is consistent with the percentage of hydrocarbon filling in Kujung-1 Reservoir. However, the fractures are in a stable condition under present-day stress. Based on further analysis, the natural fractures in the Rancak Unit are the main factor affecting the height of the hydrocarbon column in the Kujung-1 Reservoir. The Neogen compressional tectonic period is estimated to be the period of fracture in the study area in critical condition, and leakage occurred in the Kujung-1 Reservoir at that time.

Time-transgressive fault evolution and its impact on trap integrity: Timor Sea examples

2010 ◽  
Vol 50 (2) ◽  
pp. 701
Author(s):  
Bozkurt Ciftci ◽  
Laurent Langhi
Keyword(s):  
Late Jurassic ◽  
Normal Faults ◽  
Seal Integrity ◽  
Seal Failure ◽  
Hydrocarbon Traps ◽  
Exploration Risk ◽  
Timor Sea ◽  
Downward Propagation ◽  
Fault Growth ◽  
Fault Evolution

Top and fault seal failure represents an exploration risk in the Timor Sea where hydrocarbons are typically associated with hourglass structures. These structures comprise two distinct systems of conjugate normal faults that formed by 1st-phase (late Jurassic) and 2nd-phase (Neogene) extensions. Horst blocks bounded by 1st-phase faults potentially trap hydrocarbons and are overlain by grabens bounded by 2nd-phase faults. The two fault systems generally merge and intersect in dip direction to form the composite and time-transgressive faults of the hourglass structures. The 2nd-phase of extension is seen as the dominant cause of the seal breach. Revaluation of a series of hourglass structures on the Laminaria High confirmed two distinct sections of syn-kinematic strata. Bases of these sections correspond to maximum throws on the fault planes where the faults were probably nucleated. The presence of negative throw gradients upward and downward from the throw maximums indicate syn-kinematic deposition and fault growth, respectively. Assessment of these trends suggests that the 1st and 2nd-phase faults were detached at the onset of the 2nd-phase of extension. Connection was predominantly established by down-dip growth of the 2nd-phase faults while the reactivation of the 1st-phase faults may have remained minor. Seismic evidence of leakage from attribute mapping is used to constrain the timing of fault linkage and to validate prediction of leaking fault planes. It was noted that downward propagation of the 2nd-phase faults towards the hydrocarbon traps stresses the top seal integrity due to fault tip deformation front and development of sub-seismic fractures.

Geomechanical Approach in Classification of Borehole Failures in Fractured Carbonates of Boca De Jaruco Field

2021 ◽  
Author(s):  
Anna Vladimirovna Norkina ◽  
Iaroslav Olegovich Simakov ◽  
Yuriy Anatoljevich Petrakov ◽  
Alexey Evgenjevich Sobolev ◽  
Oleg Vladimirovich Petrashov ◽  
...  
Keyword(s):  
Stress State ◽  
Horizontal Wells ◽  
Horizontal Stress ◽  
In Situ Stress ◽  
Vertical Wells ◽  
Stress Regime ◽  
Geophysical Information ◽  
The Republic ◽  
Maximum Horizontal Stress

Abstract This article is a continuation of the work on geomechanically calculations for optimizing the drilling of horizontal wells into the productive reservoir M at the Boca de Haruco field of the Republic of Cuba, presented in the article SPE-196897. As part of the work, an assessment of the stress state and direction was carried out using geological and geophysical information, an analysis of the pressure behavior during steam injections, cross-dipole acoustics, as well as oriented caliper data in vertical wells. After the completion of the first part of the work, the first horizontal wells were successfully drilled into the M formation. According to the recommendations, additional studies were carried out: core sampling and recording of micro-imager logging in the deviated sections. Presence of wellbore failures at the inclined sections allowed to use the method of inverse in-situ stress modeling based on image logs interpretation. The classification of wellbore failures by micro-imager logging: natural origin and violations of technogenic genesis is carried out. The type of breakout is defined. The result of the work was the determination of the stress state and horizontal stresses direction. In addition, the article is supplemented with the calculation of the maximum horizontal stress through the stress regime identifier factor.

Stress-induced seismic azimuthal anisotropy, sand-shale content, and depth trends offshore North West Australia

Geophysics ◽  
2017 ◽  
Vol 82 (2) ◽  
pp. C77-C90 ◽  
Author(s):  
Lisa J. Gavin ◽  
David Lumley
Keyword(s):  
Confining Pressure ◽  
Horizontal Stress ◽  
Azimuthal Anisotropy ◽  
P Wave ◽  
Model Parameters ◽  
Burial Depth ◽  
3D Seismic ◽  
Depth Limit ◽  
North West ◽  
S Waves

Seismic azimuthal anisotropy is apparent when P-wave velocities vary with source-receiver azimuth and downward-propagating S-waves split into two quasi-S-waves, polarized in orthogonal directions. Not accounting for these effects can degrade seismic image quality and result in erroneous amplitude analysis and geologic interpretations. There are currently no physical models available to describe how azimuthal anisotropy induced by differential horizontal stress varies with sand-shale lithology and depth; we develop a model that does so, in unconsolidated sand-shale sequences offshore North West Australia. Our method naturally introduces two new concepts: “critical anisotropy” and “anisotropic depth limit.” Critical anisotropy is the maximum amount of azimuthal anisotropy expected to be observed at the shallowest sediment burial depth, where the confining pressure and sediment compaction are minimal. The anisotropic depth limit is the maximum depth where the stress-induced azimuthal anisotropy is expected to be observable, where the increasing effects of confining pressure, compaction, and cementation make the sediments insensitive to differential horizontal stress. We test our model on borehole log data acquired in the Stybarrow Field, offshore North West Australia, where significant differential horizontal stress and azimuthal anisotropy are present. We determine our model parameters by performing regressions using dipole shear log velocities, gamma-ray shale volume logs, and depth trend data. We perform a blind test using the model parameters derived from one well to accurately predict the azimuthal anisotropy values at two other wells in an adjacent area. We use our anisotropy predictions to improve the well-tie match of the modeled angle-dependent reflectivity amplitudes to the 3D seismic amplitude variation with offset data observed at the well locations. Future applications of our method may allow the possibility to estimate the sand-shale content over a wide exploration area using anisotropic parameters derived from surface 3D seismic data.

scholarly journals Evaluation of the Influence of In Situ Stress on the Stability of Mine Pit Walls: A Case Study of Songwe Mine

2021 ◽  
Vol 4 (2) ◽  
pp. p1
Author(s):  
Dyson Moses ◽  
Hideki Shimada ◽  
Takashi Sasaoka ◽  
Akihiro Hamanaka ◽  
Tumelo K. M Dintwe ◽  
...  
Keyword(s):  
Active Regions ◽  
Horizontal Stress ◽  
In Situ Stress ◽  
Slope Instability ◽  
Open Pit ◽  
Stress Regime ◽  
Tectonically Active ◽  
The Stability ◽  
The Impact

The investigation of the influence of in situ stress in Open Pit Mine (OPM) projects has not been accorded a deserved attention despite being a fundamental concern in the design of underground excavations. Hence, its long-term potential adverse impacts on pit slope performance are overly undermined. Nevertheless, in mines located in tectonically active settings with a potential high horizontal stress regime like the Songwe mine, the impact could be considerable. Thus, Using FLAC3D 5.0 software, based on Finite Difference Method (FDM) code, we assessed the role of stress regimes as a potential triggering factor for slope instability in Songwe mine. The results of the evaluated shearing contours and quantified strain rate and displacement values reveal that high horizontal stress can reduce the stability performance of the pit-wall in spite of the minimal change in Factor of Safety (FoS). Since mining projects have a long life span, it would be recommendable to consider “in situ stress-stability analyses” for OPM operations that would be planned to extend to greater depths and those located in tectonically active regions.

scholarly journals In Situ Stress and Stress Regime in the Onshore Part of the Northeast Java Basin

2021 ◽  
Vol 44 (2) ◽  
pp. 95-105
Author(s):  
Agus M. Ramdhan
Keyword(s):  
Petroleum Industry ◽  
Horizontal Stress ◽  
In Situ Stress ◽  
Vertical Stress ◽  
Stress Regime ◽  
Severe Erosion ◽  
Tectonically Active ◽  
Minimum Horizontal Stress ◽  
Maximum Horizontal Stress

In situ stress is importance in the petroleum industry because it will significantly enhance our understanding of present-day deformation in a sedimentary basin. The Northeast Java Basin is an example of a tectonically active basin in Indonesia. However, the in situ stress in this basin is still little known. This study attempts to analyze the regional in situ stress (i.e., vertical stress, minimum and maximum horizontal stresses) magnitude and orientation, and stress regime in the onshore part of the Northeast Java Basin based on twelve wells data, consist of density log, direct/indirect pressure test, and leak-off test (LOT) data. The magnitude of vertical (  and minimum horizontal (  stresses were determined using density log and LOT data, respectively. Meanwhile, the orientation of maximum horizontal stress  (  was determined using image log data, while its magnitude was determined based on pore pressure, mudweight, and the vertical and minimum horizontal stresses. The stress regime was simply analyzed based on the magnitude of in situ stress using Anderson’s faulting theory. The results show that the vertical stress ( ) in wells that experienced less erosion can be determined using the following equation: , where  is in psi, and z is in ft. However, wells that experienced severe erosion have vertical stress gradients higher than one psi/ft ( . The minimum horizontal stress ( ) in the hydrostatic zone can be estimated as, while in the overpressured zone, . The maximum horizontal stress ( ) in the shallow and deep hydrostatic zones can be estimated using equations: and , respectively. While in the overpressured zone, . The orientation of  is ~NE-SW, with a strike-slip faulting stress regime.

Lithology-controlled stress variations and pad-scale faults: A case study of hydraulic fracturing in the Woodford Shale, Oklahoma

Geophysics ◽  
2017 ◽  
Vol 82 (6) ◽  
pp. ID35-ID44 ◽  
Author(s):  
Xiaodong Ma ◽  
Mark D. Zoback
Keyword(s):  
Hydraulic Fracturing ◽  
Horizontal Wells ◽  
Horizontal Stress ◽  
Strike Slip ◽  
Woodford Shale ◽  
Stress Regime ◽  
Component Content ◽  
Microseismic Events ◽  
Minimum Horizontal Stress ◽  
Stress Variations

We have conducted an integrated study to investigate the petrophysical and geomechanical factors controlling the effectiveness of hydraulic fracturing (HF) in four subparallel horizontal wells in the Mississippi Limestone-Woodford Shale (MSSP-WDFD) play in Oklahoma. In two MSSP wells, the minimum horizontal stress [Formula: see text] indicated by the instantaneous shut-in pressures of the HF stages are significantly less than the vertical stress [Formula: see text]. This, combined with observations of drilling-induced tensile fractures in the MSSP in a vertical well at the site, indicates that this formation is in a normal/strike-slip faulting stress regime, consistent with earthquake focal mechanisms and other stress indicators in the area. However, the [Formula: see text] values are systematically higher and vary significantly from stage to stage in two WDFD wells. The stages associated with the abnormally high [Formula: see text] values (close to [Formula: see text]) were associated with little to no proppant placement and a limited number of microseismic events. We used compositional logs to determine the content of compliant components (clay and kerogen). Due to small variations in the trajectories of the horizontal wells, they penetrated three thin, but compositionally distinct WDFD lithofacies. We found that [Formula: see text] along the WDFD horizontals increases when the stage occurred in a zone with high clay and kerogen content. These variations of [Formula: see text] can be explained by various degrees of viscous stress relaxation, which results in the increase in [Formula: see text] (less stress anisotropy), as the compliant component content increases. The distribution of microseismic events was also affected by normal and strike-slip faults cutting across the wells. The locations of these faults were consistent with unusual lineations of microseismic events and were confirmed by 3D seismic data. Thus, the overall effectiveness of HF stimulation in the WDFD wells at this site was strongly affected the abnormally high HF gradients in clay-rich lithofacies and the presence of preexisting, pad-scale faults.

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