Fault Seal Integrity in the Timor Sea Area: Prediction of Trap Failure Using Well-Constrained Stress Tensors and Fault Surfaces Interpreted from 3D Seismic

2018 ◽  
Author(s):  
D. A. Castillo
Keyword(s):  
3D Seismic ◽  
Seal Integrity ◽  
Stress Tensors ◽  
Timor Sea ◽  
Sea Area

CALIBRATING PREDICTIONS OF FAULT SEAL REACTIVATION IN THE TIMOR SEA

2002 ◽  
Vol 42 (1) ◽  
pp. 187 ◽  
Author(s):  
S.D. Mildren ◽  
R.R. Hillis ◽  
J.Kaldi
Keyword(s):  
Shear Failure ◽  
Fault Analysis ◽  
Vertical Stress ◽  
Fault Reactivation ◽  
Power Relationship ◽  
Fault Rock ◽  
Seal Integrity ◽  
Timor Sea ◽  
Stress Profiles ◽  
Sea Area

Predictions of the likelihood of fault reactivation for five fault-bound prospects in the Timor Sea are made using the FAST (Fault Analysis Seal Technology) technique. Fault reactivation is believed to be the dominant cause of seal breach in the area. Calculations are made using a stress tensor appropriate for the area, a conservative fault-rock failure envelope and the structural geometries of each prospect. A depth-stress power relationship defines the vertical stress magnitude based on vertical stress profiles for 17 Timor Sea wells.Empirical evidence of hydrocarbon leakage at each trap is used to investigate the accuracy of the fault reactivation-based predictions of seal integrity. There is a good correlation between evidence of leakage and the risk of reactivation predicted using the FAST technique. Risk of reactivation is expressed as the pore pressure increase (ΔP) that would be required to induce failure. This study allows the fault reactivation predictions to be calibrated in terms of risk of seal breach. Low integrity traps are associated with ΔP values less than 10 MPa, moderate integrity traps correspond with values between 10 and 15 MPa and high integrity traps correspond with values greater than 15 MPa. Faults with dip magnitudes greater than 60° in the Timor Sea area are likely to have a high risk of reactivation and shear failure is the most likely mode of reactivation.

THE REGIONAL GEOLOGY OF THE BONAPARTE GULF TIMOR SEA AREA

1974 ◽  
Vol 14 (1) ◽  
pp. 77 ◽  
Author(s):  
Robert A. Laws ◽  
Gregory P. Kraus
Keyword(s):  
Late Cretaceous ◽  
Late Jurassic ◽  
Oil And Gas ◽  
Upper Jurassic ◽  
Structural Configuration ◽  
Structural Pattern ◽  
Source Areas ◽  
Timor Sea ◽  
Early Palaeozoic ◽  
Sea Area

The present structural configuration of the Bonaparte Gulf-Timor Sea area is essentially the result of Mesozoic and Tertiary fragmentation of a once relatively simple Permo-Triassic Basin. A northwest-southeast Palaeozoic structural grain in the southeastern portion of the area resulted from early Palaeozoic faulting, possibly tied to aborted rift development. This faulting effectively controlled sedimentation throughout the Phanerozoic. Pronounced northeast-southwest Jurassic to Tertiary structural trends dominate the central and northern area, paralleling the present edge of the continental shelf and swinging south southwest into the northern extension of the Browse Basin. Post-Palaeozoic epeirogenies which had the greatest effect on the regional structural pattern occurred in the mid-Jurassic, Early Cretaceous, within the Eocene and in the Plio-Pleistocene.The Kimberley and Sturt Blocks flanking the basin to the south and east constituted the most important source areas for clastic sedimentation throughout the Phanerozoic. Periodic contributions during the Mesozoic were derived from a postulated source to the northwest in the vicinity of the present-day Timor Trough.The maximum thickness of Phanerozoic sediments present within the Bonaparte Gulf-Timor Sea area exceeds 50,000 ft (15,000 m). Early Palaeozoic to Carboniferous evaporites, carbonates and clastics are unconformably overlain by a thick sequence of Permian deltaic sediments in the southeastern Bonaparte Gulf Basin. This is succeeded by a Triassic to Middle Jurassic transgressive-regressive clastic sequence, grading northwestward to marginal marine and marine clastics and carbonates. The Permian to mid-Jurassic sediments are unconformably overlain by Upper Jurassic sands and shales, mainly fluvial in the southeast and north, becoming more marine westward. These clastics are everywhere succeeded by a monotonous sequence of Cretaceous shales and shaly limestones followed by a generally north to northwesterly thickening wedge of Tertiary carbonates and minor elastics.Hydrocarbon shows have been noted offshore in rocks of Carboniferous, Permian, Late Jurassic, Late Cretaceous and Eocene age. Porous clastics in conjunction with thick and laterally-extensive, organically-rich shales are present within the Palaeozoic and Mesozoic sequences. These sediments, in association with fault- and diapir-related anomalies and stratigraphic plays, combine to make certain provinces of the Bonaparte Gulf-Timor Sea area prospective in the search for viable oil and gas reserves.

EXPLORATION IN THE NORTHERN BONAPARTE BASIN, TIMOR SEA - WA-199-P

1990 ◽  
Vol 30 (1) ◽  
pp. 7
Author(s):  
Mike Whibley ◽  
Ted Jacobson
Keyword(s):  
Late Jurassic ◽  
Fault Reactivation ◽  
Coarse Grained ◽  
3D Seismic ◽  
Submarine Fan ◽  
Oil Migration ◽  
Island Group ◽  
Main Period ◽  
Timor Sea ◽  
Exploration Phase

Permit WA-199-P, located in the Northern Bonaparte Basin, has undergone an intensive exploration phase from its award on 22 October 1985, which has resulted in the acquisition of 6250 km of 2D seismic and 1558 km of 3D seismic together with the drilling of seven exploration wells. Significant oil shows were recorded in six of these wells.The major play type investigated to date within the permit consists of Jurassic tilted horst and fault blocks. Potential reservoirs comprising medium to coarse grained sandstones of the Jurassic Plover Formation and, to a lesser extent, the Late Jurassic to Early Cretaceous Flamingo Group, are sealed by massive claystones of the Cretaceous Bathurst Island Group. Numerous oil shows have been encountered by drilling within these two reservoirs; however, drilling results from the Avocet-Eider structure indicate that Late Miocene-Recent fault reactivation often breaches the lateral seal of the fault- dependent structures causing leakage of hydrocarbons up the fault.Source extract-oil correlations and maturation studies indicate that the most likely oil sources comprise thermally mature marine claystones of the Flamingo Group and Plover Formation, developed within the Sahul Syncline to the east of WA-199-P. The main period of oil migration was probably Miocene or younger. A number of play types remain untested. These consist of Permian, Intra-Triassic and top Cretaceous fault blocks, as well as fault-independent closures, downdip fault closures and stratigraphic wedge outs of Maastrichtian sand reservoirs, and submarine fan sands developed within the basal Flamingo Group.

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.

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.

FAULT ARCHITECTURE ANDTHE MECHANICS OF FAULT REACTIVATION INTHE NANCARTROUGH/LAMIN ARIA AREA OF THE TIMOR SEA, NORTHERN AUSTRALIA

2000 ◽  
Vol 40 (1) ◽  
pp. 174 ◽  
Author(s):  
M.J. de Ruig M. Trupp ◽  
D.J. Bishop ◽  
D. Kuek ◽  
D.A. Castillo
Keyword(s):  
Late Miocene ◽  
Seismic Data ◽  
Fault Plane ◽  
Fault Reactivation ◽  
3D Seismic ◽  
Oblique Collision ◽  
Late Tertiary ◽  
Timor Sea ◽  
Fault Architecture ◽  
3D Seismic Data

Fault-bounded Jurassic structures of the Timor Sea have in recent years been the focus of intensive oil exploration. A number of significant oil discoveries have highlighted the exploration potential of this area (e.g. Laminaria, Corallina, Buffalo, Elang, Kakatua), but the majority of tested structures are either underfilled or show evidence of a residual oil column, resulting from trap failure of previously hydrocarbon-bearing structures. Recent well results confirm that trap integrity remains the principal exploration risk in the Timor Sea.Fault reactivation of Jurassic hydrocarbon traps is related to late Miocene-Pliocene oblique collision between the Australian plate and the SE Asian plate complex, which caused widespread transtensional faulting. The sealing potential of fault-bounded traps is, to a large degree, controlled by the orientation of the fault plane relative to the late Miocene-Recent stress field. However, the location of potential hydrocarbon leakage pathways remains difficult to define due to the complex fault architecture and a limited understanding of the interaction between Jurassic faults and Late Tertiary tectonism.During the past few years, a wealth of new exploration wells and 3D seismic data has become available from the Laminaria High/Nancar Trough area. The use of 3D visualisation tools, seismic coherency filtering and other seismic techniques has greatly enhanced our understanding of the fault architecture of this area of the Timor Sea.The structural architecture of the Nancar Trough/ Laminaria High is made up of several different structural intervals that are stratigraphically separated and partially decoupled along thick claystone intervals. Fault blocks at Jurassic level are typically overlain by Tertiary en-echelon graben systems, often showing characteristic 'hourglass' structures in cross-section. Detailed mapping of these fault structures on 3D seismic data has shown that the Jurassic faults and overlying Tertiary faults areoften partially decoupled.Fault throw distributions indicate that the Mio-Pliocene faults have grown downwards instead of Jurassic faults propagating upwards during reactivation. The two fault systems are soft-linked within Cretaceous claystones, only locally linking to form through-going faults. Hydrocarbon leakage pathways are most likely located at these points where critically stressed parts of Jurassic faults link up with Tertiary faults. The position of these linkage zones in relation to structural closure is key to understanding the distribution of preserved and breached columns that have been observed to date.The integration of 3D seismic fault plane mapping with in-situ stress analysis from borehole image and pressure test data provides a valuable tool for the evaluation of trap integrity, potential hydrocarbon leak paths and a more accurate risk assessment of exploration prospects.

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