DYNAMIC FAULT/FRACTURE SEAL BEHAVIOUR AND GEOMECHANICAL ANALYSIS OF THE GREATER GOBE AREA, SOUTHERN HIGHLANDS PROVINCE, PAPUA NEW GUINEA

2001 ◽  
Vol 41 (1) ◽  
pp. 251
Author(s):  
M.C. Daniels ◽  
D.T. Moffat ◽  
D.A. Castillo
Keyword(s):  
Papua New Guinea ◽  
Shear Failure ◽  
New Guinea ◽  
In Situ Stress ◽  
Stress Regime ◽  
Well Spacing ◽  
Geomechanical Analysis ◽  
Near Shore ◽  
Performance Results

The Gobe Main and SE Gobe Fields were discovered in the early 1990s in the Papuan Fold Belt in the Highlands of Papua New Guinea. Heavily karstified Darai Limestone at the surface and heli-supported drilling made field appraisal problematic and expensive. With initial well spacing upwards of several kilometres, these fields were thought to be ‘tank’ type models, with field-wide extrapolations of gas-oil and oil-water contacts.The main Iagifu Sandstone reservoir in the Gobe fields comprises several fluvial and near-shore sand bodies, which are readily correlatable across the fields. The reservoir units display discrete coarsening upward sequences containing medium (~17%) porosity, medium to high permeability (>100 mD) sandstones. Although several different depositional facies are interpreted within the Iagifu reservoir, sand units are extensive on the scale of the Gobe structures and do not appear to be producing significant lateral boundaries or reservoir compartmentalisation.Geomechanical analysis has enabled the calculation of in-situ stress magnitudes and establishment of a geomechanical model for Gobe. Locally, the Gobe Main Field appears to be in a strike-slip stress regime (SHmax>Sv>Shmin). SHmax directions vary from NNE– SSW to NE–SW. Stress magnitudes indicate the structure is near frictional equilibrium, with a high proportion of natural fractures and faults critically stressed for shear failure. Since first oil in early 1998, performance results have indicted pressure segregation of many of the wells in both the Gobe Main and SE Gobe fields. Although only one fault has been positively identified at the reservoir level, the mapped faults appear to have sand-on-sand juxtaposition with minimal (

scholarly journals Geomechanical Analysis for Deep Shale Gas Exploration Wells in the NDNR Blocks, Sichuan Basin, Southwest China

Energies ◽  
2020 ◽  
Vol 13 (5) ◽  
pp. 1117 ◽  
Author(s):  
Majia Zheng ◽  
Hongming Tang ◽  
Hu Li ◽  
Jian Zheng ◽  
Cui Jing
Keyword(s):  
Pore Pressure ◽  
Shale Gas ◽  
Sichuan Basin ◽  
In Situ Stress ◽  
Wellbore Stability ◽  
Geomechanical Model ◽  
Stress Regime ◽  
Xujiahe Formation ◽  
Geomechanical Analysis

The abundant reserve of shale gas in Sichuan Basin has become a significant natural gas component in China. To achieve efficient development of shale gas, it is necessary to analyze the stress state, pore pressure, and reservoir mechanical properties such that an accurate geomechanical model can be established. In this paper, Six wells of Neijiang-Dazu and North Rongchang (NDNR) Block were thoroughly investigated to establish the geomechanical model for the study area. The well log analysis was performed to derive the in-situ stresses and pore pressure while the stress polygon was applied to constrain the value of the maximum horizontal principal stress. Image and caliper data, mini-frac test and laboratory rock mechanics test results were used to calibrate the geomechanical model. The model was further validated by comparing the model prediction against the actual wellbore failure observed in the field. It was found that it is associated with the strike-slip (SS) stress regime; the orientation of SHmax was inferred to be 106–130° N. The pore pressure appears to be approximately hydrostatic from the surface to 1000 m true vertical depth (TVD), but then becomes over-pressured from the Xujiahe formation. The geomechanical model can provide guidance for the subsequent drilling and completion in this area and be used to effectively avoid complex drilling events such as collapse, kick, and lost circulation (mud losses) along the entire well. Also, the in-situ stress and pore pressure database can be used to analyze wellbore stability issues as well as help design hydraulic fracturing operations.

Cationic Substitutions in Sphalerite from the Porgera Mine, Papua New Guinea

2021 ◽  
Author(s):  
Christopher H. Ingles ◽  
John A. Mavrogenes
Keyword(s):  
Solid Solution ◽  
Papua New Guinea ◽  
Solid Solutions ◽  
Inductively Coupled Plasma ◽  
New Guinea ◽  
Inductively Coupled ◽  
Cationic Substitution ◽  
Plasma Mass Spectrometry ◽  
Positive Correlations

ABSTRACT Laser ablation-inductively coupled plasma-mass spectrometry was used to traverse hydrothermal vein sphalerite from different ore-forming stages of the Porgera Au-Ag mine, Papua New Guinea. Elements were measured in situ over the growth of crystals to investigate the greatly varying concentrations of cations in sphalerite and their positions in the lattice. Traverse profiles for 16 elements were obtained and aligned to transmitted light images where possible. Each sample contained an array of elements, with many displaying orders of magnitude concentration differences. Results show the simultaneous incorporation of Cu and Sn in sphalerite, as well as Cu and Ag, In and Sn, As and Sb, Fe and Mn, and Cu and Ga. The relation [4Zn2+ ↔ 2Cu+ + Sn2+ + Sn4+] is proposed to explain the 1:1 Cu–Sn correlation. Further relations can be seen, including a Ga “ceiling” or Cu “floor”, where Ga incorporation becomes dependent on Cu concentrations. Furthermore, silver was also observed to correlate with Au, Mn, Ni, Pb, and Bi. Meta-stable solid solutions between pairs such as Cu, Ag; Fe, Mn; As, Sb; and In, Sn are also suggested. Each of these pairs are neighbors on the periodic table of elements, which suggests that simple solid solution can occur, and positive correlations for all four solid solutions were found in one sample alone. While the concept of charge-specific solid solutions in sphalerite has been discussed in the literature with reference to monovalent cations, the results presented herein also indicate solid solutions of higher oxidation states, containing many cations. Furthermore, while cations in charge-specific solid solutions have been proposed to compete for lattice sites in sphalerite, simultaneous in situ coupled concentrations at Porgera suggest otherwise. Cationic substitution equations displaying decimal ratios of each element in solid solution can then provide a novel method to distinguish between solid solution concentrations in different samples. For example, displaying 1:1 ratios of Cu–Ag and Sb–As: [2Zn2+ ↔ (Cu+0.5, Ag+0.5) + (As3+0.5, Sb3+0.5)], or for a 100:1 Fe–Mn ratio: [Zn2+ ↔ (Fe2+0.99, Mn2+0.01)].

APPLICATION OF GUIDELINE CHARTS IN DECISIONMAKING ON WELL TRAJECTORY AND MUD WEIGHT PROGRAM

2001 ◽  
Vol 41 (1) ◽  
pp. 609
Author(s):  
X. Chen ◽  
C.P. Tan ◽  
C.M. Haberfield
Keyword(s):  
Stability Analysis ◽  
Case Studies ◽  
In Situ Stress ◽  
Wellbore Stability ◽  
Material Strength ◽  
Stress Regime ◽  
Wellbore Instability ◽  
Well Trajectory

To prevent or minimise wellbore instability problems, it is critical to determine the optimum wellbore profile and to design an appropriate mud weight program based on wellbore stability analysis. It is a complex and iterative decisionmaking procedure since various factors, such as in-situ stress regime, material strength and poroelastic properties, strength and poroelastic anisotropies, initial and induced pore pressures, must be considered in the assessment and determination.This paper describes the methodology and procedure for determination of optimum wellbore profile and mud weight program based on rock mechanics consideration. The methodology is presented in the form of guideline charts and the procedure of applying the methodology is described. The application of the methodology and procedure is demonstrated through two field case studies with different in-situ stress regimes in Australia and Indonesia.

Defining structural permeability in Australian sedimentary basins

2015 ◽  
Vol 55 (1) ◽  
pp. 119 ◽  
Author(s):  
Adam Bailey ◽  
Rosalind King ◽  
Simon Holford ◽  
Joshua Sage ◽  
Martin Hand ◽  
...  
Keyword(s):  
Regional Scale ◽  
Sedimentary Basins ◽  
In Situ Stress ◽  
Natural Fracture ◽  
Enhanced Geothermal Systems ◽  
Structural Development ◽  
Geothermal Systems ◽  
Stress Regime ◽  
Orientation Data

Declining conventional hydrocarbon reserves have triggered exploration towards unconventional energy, such as CSG, shale gas and enhanced geothermal systems. Unconventional play viability is often heavily dependent on the presence of secondary permeability in the form of interconnected natural fracture networks that commonly exert a prime control over permeability due to low primary permeabiliy of in situ rock units. Structural permeability in the Northern Perth, SA Otway, and Northern Carnarvon basins is characterised using an integrated geophysical and geological approach combining wellbore logs, seismic attribute analysis and detailed structural geology. Integration of these methods allows for the identification of faults and fractures across a range of scales (millimetre to kilometre), providing crucial permeability information. New stress orientation data is also interpreted, allowing for stress-based predictions of fracture reactivation. Otway Basin core shows open fractures are rarer than image logs indicate; this is due to the presence of fracture-filling siderite, an electrically conductive cement that may cause fractures to appear hydraulically conductive in image logs. Although the majority of fractures detected are favourably oriented for reactivation under in situ stresses, fracture fill primarily controls which fractures are open, demonstrating that lithological data is often essential for understanding potential structural permeability networks. The Carnarvon Basin is shown to host distinct variations in fracture orientation attributable to the in situ stress regime, regional tectonic development and local structure. A detailed understanding of the structural development, from regional-scale (hundreds of kilometres) down to local-scale (kilometres), is demonstrated to be of importance when attempting to understand structural permeability.

Yielding and rupture in a lacustrine clay

1980 ◽  
Vol 17 (4) ◽  
pp. 559-573 ◽  
Author(s):  
A. Baracos ◽  
J. Graham ◽  
L. Domaschuk
Keyword(s):  
Shear Failure ◽  
Friction Angle ◽  
In Situ Stress ◽  
Grain Structure ◽  
Testing Procedures ◽  
Straight Line ◽  
Stress Levels ◽  
Lacustrine Clay ◽  
Field Behaviour

Recent tests have examined the properties of block samples and tube samples from depths to 12 m in Winnipeg clay. Careful trimming and a wide variety of testing procedures have permitted new insights into the behaviour of the clay that is markedly anisotropic and non-homogeneous. The effective strength envelope for "blue clay" from 6 to 12 m depth can be simplified into three straight-line sections. At low stresses, a section of the envelope has been identified having a low cohesion intercept and a high "friction" angle. This is thought to be caused by close Assuring in the clay, and controls the field behaviour in many small embankment, riverbank, and excavation problems. At in situ stress levels, the clay dilates markedly as failure is approached. Porewater pressures depend strongly on stress levels during laboratory reconsolidation. Residual strengths are low, and are influenced by the methods used during testing. Yielding has been clearly identified for shear failure of the grain structure, but is more poorly defined for increasing normal octahedral stresses. The work has emphasized the importance of selecting appropriate testing procedures and stresses for field applications.

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.

scholarly journals Numerical Investigation of the Impacts of Borehole Breakouts on Breakdown Pressure

Energies ◽  
2019 ◽  
Vol 12 (5) ◽  
pp. 888 ◽  
Author(s):  
Hua Zhang ◽  
Shunde Yin ◽  
Bernt Aadnoy
Keyword(s):  
Hydraulic Fracturing ◽  
Shear Failure ◽  
In Situ Stress ◽  
Test Results ◽  
Breakdown Pressure ◽  
Borehole Breakout ◽  
Borehole Breakouts ◽  
The Difference ◽  
Mud Pressure

Borehole breakouts appear in drilling and production operations when rock subjected to in situ stress experiences shear failure. However, if a borehole breakout occurs, the boundary of the borehole is no longer circular and the stress distribution around it is different. So, the interpretation of the hydraulic fracturing test results based on the Kirsch solution may not be valid. Therefore, it is important to investigate the factors that may affect the correct interpretation of the breakdown pressure in a hydraulic fracturing test for a borehole that had breakouts. In this paper, two steps are taken to implement this investigation. First, sets of finite element modeling provide sets of data on borehole breakout measures. Second, for a given measure of borehole breakouts, according to the linear relation between the mud pressure and the stress on the borehole wall, the breakdown pressure considering the borehole breakouts is acquired by applying different mud pressure in the model. Results show the difference between the breakdown pressure of a circular borehole and that of borehole that had breakouts could be as large as 82% in some situations.

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