Tài liệu Characterizing the full in situ stress tensor and its applications for petroleum activities

Doctoral Dissertation Characterizing the Full In-Situ Stress Tensor and Its Applications for Petroleum Activities Department of Energy and Resources Engineering Graduate School, Chonnam National University Do Quang Khanh August 2013 Characterizing the Full In-Situ Stress Tensor and lts Applications for Petroleum Activities Department of Energy and Resources Engineering Graduate School. Chonnam National Universitv Do Quang Khanh Supervised by Professor YANG, Hyung-Sik A dissertation submitted in partial fulfillment of the requirements for the Doctor of Philosophy in Energy and Resources Engineering. Committee in Charge Dr. : So-Keul GAM) Prof. Tam T Prof. Jeong-Flwan Lee Prol-. Piyush Rai (CNU) ilffi"4-- (BHU, India) Prof. Hyung-Sik Yans (CNU) August 2013 )z 4 -3- CONTENTS Characterizing the Full In-Situ Stress Tensor and Its Applications for Petroleum Activities Contents i List of figures and tables iv Nomenclature of symbols viii Abstract x CHAPTER 1: INTRODUCTION 1 1.1. Project rationale 1 1.2. Project philosophy and purposes 2 1.3. Review 3 1.4. Outline of thesis 7 CHAPTER 2: IN-SITU STRESS TENSOR AND ITS RELATING CONCEPTS 9 2.1. Introduction 9 2.2. In-situ stress tensor 9 2.3. State of in-situ stress 13 2.4. Pore pressure and effective stress 14 2.5. Frictional limits to stress 15 2.6. Stresses and rock failure 17 CHAPTER 3: STRESS AND FAILURE ANALYSIS FOR WELLBORES 22 3.1. Introduction 22 3.2. Stress and failure analysis for a vertical cylindrical wellbore 22 3.2.1. Stresses around a vertical cylindrical wellbore 22 3.2.2. Failure analysis for a vertical wellbore 26 3.3. Stress and failure analysis for an arbitrarily deviated wellbore 28 3.3.1. Stresses around an arbitrarily deviated wellbore 28 3.3.2. Failure analysis for an arbitrary deviated wellbore 33 i CHAPTER 4: METHODS FOR DETERMINING IN-SITU STRESS 35 4.1. In-situ stress measurements in drilling boreholes 35 4.1.1. Hydraulic fracturing methods 35 4.1.2. Overcoring methods 37 4.1.3. Breakout methods 39 4.1.4. Drilling induced tensile fractures methods 43 4.1.5. Earth focal mechanism (FMS) 45 4.2. New integrated method for determining ISS using petroleum exploration data 47 4.2.1. Introduction 47 4.2.2. Determining the orientations of horizontal stresses 49 4.2.3. Determining the vertical stress 51 4.2.4. Determining the minimum horizontal stress magnitude 54 4.2.5. Constraining the maximum horizontal stress magnitude 57 4.2.6. Determining pore pressure 62 CHAPTER 5: MODEL DEVELOPMENT FOR FAILURE ANALYSIS OF WELLBORE (FAOWB) 65 5.1. Introduction 65 5.2. Structures of the FAoWB software packages 65 5.3. Validation of the results of the packages FAoWB 71 5.3.1. Case 1: Cross-checking Barton’s study (1998) on compressive failure and breakout width analysis at the KTB wellbore, Germany. 71 5.3.2. Case 2: Cross-checking Meyer’s study (2002) on the well stability at the Swan Lake field, South Australia. 78 CHAPTER 6: CASE STUDIES AND IMPLICATIONS 89 6.1. Introduction 89 6.2. Geological framework of the main studied area 89 6.3. The White Tiger (Bach Ho) field, Centre of the Cuu Long basin, Vietnam 93 6.3.1. Statement of problem 93 6.3.2. In-situ stress determination techniques 96 6.3.3. In-situ stress tensor at the White Tiger field 105 6.3.4. Implications 106 6.3.5. Summary of results 120 ii 6.4. The X field, Northern of the Cuu Long basin, Vietnam 121 6.4.1. Statement of problem 121 6.4.2. In-situ stress determination techniques 123 6.4.3. In-situ stress tensor at the X field 129 6.4.4. Implications 130 6.4.5. Summary of results 135 CHAPTER 7: CONCLUSIONS AND RECOMMENDATIONS 137 Reference 140 Abstract in Korean 148 Acknowledgements 150 iii LIST OF FIGURES AND TABLES Figure 2.1: Components of stresses acting on a plane. 10 Figure 2.2: Components of stresses acting on the faces of a cube. 11 Figure 2.3: The three states of stress and associated types of faulting. 13 Figure 2.4: Frictional limits to stress based on the frictional strength of favourably oriented fault planes for μ = 0.6 and 1.0. 17 Figure 2.5: Two-dimensional Mohr circle. 18 Figure 2.6: Three-dimensional Mohr circle. 19 Figure 2.7: Mohr diagram with a failure envelope that fits closely to laboratory rock testing data. 20 Figure 2.8: Three-dimensional Mohr diagram and Coulomb failure criterions for pre-existing planes of weakness and for intact rock. 21 Figure 3.1: Vertical cylindrical wellbore with the orientations of the circumferential stress σϴϴ, axial stress σzz and radial stress σrr. 23 Figure 3.2: Stress concentration around a vertical in a bi-axial stress field based on the Kirsch equations. 24 Figure 3.3: The stress concentration around a circular borehole subject to only uniaxial compression. 25 Figure 3.4: An arbitrarily deviated wellbore with the orientations of the cirumferential (σϴϴ), axial (σzz), radial (σrr), minimum (tmin) and maximum (tmax) stresses. 29 Figure 3.5: Three coordinate systems used to transform for an arbitrarily deviated wellbore. 30 Figure 3.6: Lower hemisphere projection used to display relatively stability of wellbores with different azimuths and deviations. 34 Figure 4.1: A schematic diagram with the equipment set-up and the propagation direction of the induced fracture during a hydraulic fracturing test. Figure 4.2: Typical procedure used in the overcoring technique 36 38 Figure 4.3: Circumferential stress around a vertical wellbore with respect to the orientation of the maximum horizontal stress iv for formation of BOs and DITFs. 40 Figure 4.4: Section of four-arm dipmeter log data showing consistent breakouts in a north-south direction. 41 Figure 4.5: An imaging log data with borehole breakouts. 42 Figure 4.6: Hollow cylinder laboratory test. 42 Figure 4.7: An imaging log data with drilling induced tensile fractures 44 Figure 4.8: The three main fault regimes and their corresponding fault plane solutions. Figure 4.9: Integration of density logs to estimate overburden stress at depths 46 52 Figure 4.10: Resistivity image, density log (RHOB), density correction log (DRHO) and caliper log (CALI). 53 Figure 4.11: Pressure vs. time record showing LOP, breakdown, Pc and Pr. 55 Figure 4.12: Pressure versus root time plot showing Pc. 57 Figure 5.1: Start screen of the software packages FAoWB. 66 Figure 5.2: Main screen of the software packages FAoWB. 66 Figure 5.3: Menu File of the software packages FAoWB. 66 Figure 5.4: Menu Input Data of the software packages FAoWB. 67 Figure 5.5: Tab Description of the software packages FAoWB. 67 Figure 5.6: Tab Stress of the software packages FAoWB. 68 Figure 5.7: Tab Rock properties of the software packages FAoWB. 68 Figure 5.8: Tab Well of the software packages FAoWB. 69 Figure 5.9: Menu Failure Criteria of the software packages FAoWB. 69 Figure 5.10: Menu Process of the software packages FAoWB. 70 Figure 5.11: Menu Output of the software packages FAoWB. 70 Figure 5.12: Stress distribution of case 1 (from packages FAoWB). 72 Figure 5.13: Risk diagrams of case 1 (from packages FAoWB). 73 Figure 5.14: The breakout risk diagrams of the KTB wells for Mohr-Coulomb, Drucker-Prager and Mogi-Coulomb criteria. 74 Figure 5.15: The mud weight required of the KTB wells. 76 Figure 5.16: Risk diagrams of case 2 (from packages FAoWB). 79 Figure 5.17: The breakout risk diagrams of wells at Swan Lake field for Mohr-Coulomb, Drucker-Prager and Mogi-Coulomb criteria. 81 Figure 5.18: The mud weight required at the Swan Lake field. 82 Figure 5.19: Stress distribution of case 2 (from packages FAoWB). 84 v Figure 5.20: Stress polygon and constraints for case 1 and 2. 86 Figure 6.1: Location map of the Cuu Long Basin. 90 Figure 6.2: Schematic cross-section of the Cuu Long Basin. 91 Figure 6.3:Generalized stratigraphy column of the Cuu Long Basin. 92 Figure 6.4. Location map of the White Tiger field at the Cuu long basin. 93 Figure 6.5: Basement distribution at White Tiger field, Cuu Long basin. 94 Figure 6.6: Main fault and fracture system at the White Tiger field. 95 Figure 6.7: Generalized stratigraphy column at the White Tiger. 95 Figure 6.8: Examples of the occurrence of BOs and DIFTs at the basement intervals of the wellbores at the White Tiger field. 96 Figure 6.9: Histogram and rose diagrams of the orientation of SHmax from BOs at the basement intervals of the Whiter Tiger field. 97 Figure 6.10: Histogram and rose diagrams of of the orientation of SHmax from DITFs at the basement intervals of the Whiter Tiger field. 97 Figure 6.11: Histogram and rose diagrams of the orientation of SHmax from both BOs and DITFs at the basement intervals of the Whiter Tiger field. 98 Figure 6.12: Vertical stress or overburden stress at the White Tiger field. 99 Figure 6.13: Plots of treatment pressure in the hydraulic fracturing tests. 99 Figure 6.14: Minimum horizontal stress at the White Tiger field. 100 Figure 6.15: Pore pressure at the White Tiger field. 101 Figure 6.16: Stress Polygon and constraints at depths of the White Tiger field. 104 Figure 6.17: Stress distribution at the depth 3900 m of the White Tiger field. 106 Figure 6.18: Stress distribution at the depth 4100 m of the White Tiger field. 107 Figure 6.19: Stress distribution at the depth 4300 m of the White Tiger field. 108 Figure 6.20: Stress distribution at the depth 4500 m of the White Tiger field. 109 Figure 6.21: Risk diagrams at the depth 3900 m of the White Tiger field. 110 Figure 6.22: Risk diagrams at the depth 4100 m of the White Tiger field. 113 Figure 6.23: Risk diagrams at the depth 4300 m of the White Tiger field. 116 Figure 6.24: Risk diagrams at the depth 4500 m of the White Tiger field. 118 Figure 6.25: Location map of the X field. 121 Figure 6.26: The depth structural map at the X field. 121 Figure 6.27: The stratigraphy column of the X field. 122 Figure 6.28: Example of DITFs of the wellbore X1 at the X field. 123 Figure 6.29: Histogram and rose diagrams of DITFs at the wellbore X1. 124 vi Figure 6.30: Vertical stress or overburden stress at the X field. 125 Figure 6.31: Plots of surface pressure in the LOTs/FITs at the X field. 126 Figure 6.32: Minimum horizontal stress at the X field. 126 Figure 6.33: Pore pressure at the X field. 127 Figure 6.34: Stress Polygon and constraints at depth 2300 m of the X field. 128 Figure 6.35: Stress distribution at the basement depth 2300 m of the X field. 130 Figure 6.36: Risk diagrams at the basement depth 2300 m of the X field. 131 Figure 6.37: Risk diagrams on evaluation for the applicability of under-balanced drilling techniques (Pw=22 MPa). Figure 6.38: Stress distribution at two deviated wellbores of the X field. 134 135 Table 6.1: The full in-situ stress tensor at the basement depths of the White Tiger field. 105 Table 6.2: The full in-situ stress tensor at the basement depth 2300 m of the X field. 129 vii NOMENCLATURE OF SYMBOLS C: compressive strength C0: uniaxial compressive strength Cb: biaxial compressive strength g: acceleration due to gravity P: stress tensor due to pore pressure Pc: fracture closure pressure Pi: fracture initiation pressure Pp: pore pressure Pr: fracture reopening pressure Pw: wellbore fluid pressure Rb: coordinate transform matrix RS: coordinate transform matrix S: applied stress tensor S’: effective stress tensor S1, S2, S3: three principal stresses Sb: stress tensor in the borehole coordinate system Sg: stress tensor in the geographic coordinate system SHmax: maximum horizontal stress magnitude Shmin minimum horizontal stress magnitude Ss: stress tensor in principal stress coordinate system Sv: vertical stress magnitude T: tensile strength z: depth α, β, γ: Euler rotation angles δ: wellbore azimuth viii δij: Kronecker delta ΔP: difference between wellbore and pore pressure μ: coefficient of friction ʋ: Poisson’s ratio ƍ: density σij: stress component acting in the j direction in the plane normal to the i direction σn: normal stress σrr: effective radial stress σtmax: maximum effective stress tangential to the wellbore wall σtmin: minimum effective stress tangential to the wellbore wall σzz: effective axial stress σϴϴ: effective circumferential stress σϴϴmin: minimum of the effective circumferential stress φ: wellbore deviation ω: angle between σtmax and the wellbore axis : shear stress ix Characterizing the Full In-Situ Stress Tensor and Its Applications for Petroleum Activities Do Quang Khanh Department of Energy and Resources Engineering Graduate School, Chonnam National University (Supervised by Professor YANG, Hyung-Sik) (Abstract) Knowledge of the full in-situ stress tensor has an importance for petroleum activities. A demand in the determination of in-situ stress using petroleum exploration data available has increased during the last decades over the world. The new integrated method for determining the full in-situ stress tensor using the available petroleum data has been accepted as more reliable and widely applicable in many petroleum basins. This thesis developed and applied the new integrated method for determining the full tensor of in-situ stress using the available petroleum data. This method involves many aspects in which the constraining related to the magnitude of the maximum horizontal stress is the most challenge. It also requires the integration and modification many techniques for studying specific problems using available datasets. x The software packages on failure analysis of wellbores (FAoWB) written in the programming language MATLAB were designed and developed from this new integrated method for determining the full stress tensor and the extended theories on stresses and failures around the wellbore. They facilitate the determination of the full in-situ stress tensor using the observations of wellbore failures (breakouts BOs and/or drilling-induced tensile fractures DIFTs) in petroleum wellbores. The forward calculating of stresses around the wellbores will be constrained with the observations of borehole failures and rock strength, pore pressure or mud pressure depending on available data at a particular petroleum field. Moreover, under the full in-situ stress tensor determined they also help to derive easily the implications related to the state of in-situ stress. Their accuracy and reliability were confirmed through the cross-checking of two well-known investigations earlier. Three different strength criteria including the MohrCoulomb, Drucker-Prager and Mogi-Coulomb criteria also were applied to recommend the selection of an appropriate criterion for relatively strong rocks. Furthermore, they have been demonstrated to be user-friendly, attractive and easy to develop the codes for other real cases. The software packages FAoWB were used to characterize well the state of the full in-situ stress tensors from the new integrated method with available data of basement reservoirs of the petroleum fields belonging to the Cuu Long basin, Vietnam. Those are the White Tiger field located at the centre of xi the Cuu Long basin and the X field located at the northern of the Cuu Long basin. Results showed that the stress regimes at basement reservoirs of the Cuu Long basin should be the normal faulting (NF) or the strike-slip (SS) with the orientation of the maximum horizontal stress oriented in the direction NW-SE being consistent with the previous studies. The change of the stress regimes from NF to SS together with the strength rock measured should affect the risk of the occurrence of BOs and/or DITFs. These predictions are suitable to the practical problems at the petroleum fields of this basin as the wellbore collapse (due to BOs) or the lost circulation (due to DITFs). Moreover, with advanced knowledge of the full in-situ stress tensors including both the orientations and magnitudes, we could choose the optimum drilling trajectories oriented in the direction NE-SW, change the suitable mud weight to prevent wellbore instability or evaluate the applicability of underbalanced drilling techniques at the petroleum fields of the Cuu Long basin. Keywords: In-situ stress, wellbore failures, breakouts, drilling-induced tensile fractures, wellbore instability. xii CHAPTER 1 INTRODUCTION 1.1. Project rationale Knowledge of in-situ stress plays a great role in solving both science and engineering problems, encountered in geology, geophysics, civil, mining, and petroleum development. It is a key parameter in some activities including (Amadei and Stephansson, 1997; Tingay et al, 2009): · plate tectonics and neotectonics; · earthquake prediction and seal breach by fault reactivation; · stability of underground excavations (tunnels, mines, caverns, shafts, stopes); · slope stability; · drilling borehole stability; · induced hydraulic fracturing stimulation; · reservoir drainage and flooding patterns; · subsurface fluid flow in naturally-fractured reservoirs, and · storage and extraction of oil and gas from the subsurface. A dramatic increase in the determination of in-situ stress using petroleum exploration data and its applications to problems in petroleum exploration and production has been seen during the last decades over the world. One key driver for the increased awareness has been the increasing quality and use of borehole imaging tools, and the geomechanical information yielded by these tools. Nowadays, drilling induced failures including breakouts and/or drilling induced tensile fractures from borehole imaging tools are recognized and used to determine in-situ stress (Zoback et al., 1985; Peska and Zoback, 1995). Furthermore, the 1 increased incidence of deviated drilling has provided both new techniques for constraining the in situ stress tensor and increased demand for solutions to problems related to the stateof-stress such as wellbore stability and fracture stimulation. 1.2. Project philosophy and purposes There have been a number of different methods available to determine the in-situ stress in the Earth’s crust. These methods include earthquake focal mechanisms, hydraulic fracturing, overcoring, borehole breakouts, drilling induced tensile fractures and geological indicators. Each stress measurement technique has advantages and limitations. The relationship between in situ stress and induced failures in drilling boreholes can have significant implications for in-situ stress determination methods. Therefore, the philosophy of this project was to integrate and/or modify techniques as required for studying specific problems using available datasets in the case studies. In-situ stress determination in any oil field or sedimentary basin involves some aspects, such as determination of the maximum horizontal stress orientations, the magnitude of the vertical stress, the magnitude of the minimum horizontal stress and the constraining related to the magnitude of the maximum horizontal stress. The approach to aspects of stress determination is dependent upon the dataset available. The main purpose of this project is to formulate and apply the new integrated method for determining the full tensor of in-situ stress based on new and existing techniques from available petroleum data. Next, the use of these techniques within several case studies at the petroleum fields will be analyzed to examine the wide range of implications of in situ stress data to petroleum exploration and production activities. A significant part of this project has involved designing and developing the software packages on failure analysis of wellbores (FAoWB) written by programming language MATLAB. They facilitate the determination of the full in-situ stress tensor using the observations of wellbore failures in petroleum wellbores. Moreover, under the full in-situ 2 stress tensor determined the FAoWB software packages also help to derive easily the implications related to the state of in-situ stress, such as the choice of the optimum drilling trajectories for wellbore planning and the suitable mud weights for well stability. 1.3. Review During the last decades there has been extensive research on the determination of in situ stresses and its applications, particularly in the petroleum industry. To provide a contextual framework for the more detailed discussion of the new integrated method for the in-situ stress determination based new and existing techniques, a brief review of existing techniques is presented here. Generally, in sedimentary basins occurred the petroleum activities, the vertical stress is a principal stress. Consequently the full in-situ stress tensor can be reduced to four components. These components are the orientation of the maximum horizontal stress, the vertical stress magnitude (Sv), the minimum horizontal stress magnitude (Shmin) and the maximum horizontal stress magnitude (SHmax). The orientation of the maximum horizontal stress can be determined from observations of breakouts and drilling-induced tensile fractures commonly seen on borehole image logs. Borehole breakouts (BOs) were first described by Bell and Gough (1979) as stress-induced compressive failure of the wellbore, and have subsequently been used to determine maximum horizontal stress orientations throughout the world (Zoback and Zoback, 1980; Plumb and Cox, 1987, etc.). The advent of borehole imaging tools has confirmed the nature of breakouts and has led to the recognition of stress-induced tensile wellbore failure known as drilling induced tensile fractures (DITFs). DITFs are oriented orthogonal to breakouts and can also be used to determine the orientation of the maximum horizontal stress (Aadnoy, 1990b; Brudy and Zoback, 1993, etc.). The vertical stress magnitude can be determined from the weight of the overburden (McGarr 3 and Gay, 1978), which can be calculated using density logs and checkshot velocity surveys. Density logs are routinely run during petroleum exploration and conventionally provide a density measurement every 15 cm. However, density logs are rarely run to the surface resulting in a lack of shallow data. Density in the shallow section can be estimated by transforming sonic velocity from a checkshot velocity survey (Ludwig et al., 1970). Hydraulic fracture test is an early and reliable method for determining in situ horizontal stress magnitudes and orientations (Haimson and Fairhurst, 1967). Hydraulic fracture tests involve isolating a section of the wellbore and increasing the pressure in the isolated interval by pumping fluid into it, and thereby creating a fracture in the wellbore wall. This fracture forms parallel to the wellbore axis (for a vertical wellbore) and orthogonal to the minimum horizontal stress. In general the fracture propagates away from the wellbore in this orientation as fluid continues to be pumped into the interval. In a thrust faulting stress regime the fracture may rotate to horizontal, as it propagates away from the wellbore, complicating the analysis. However, in general it is the minimum horizontal stress that acts to close the fracture (Hubbert and Willis, 1957), and consequently the pressure at which the fracture closes is a measure of the minimum horizontal stress and can be determined from the pressure versus time record (Haimson and Fairhurst, 1967, etc.). In petroleum drilling, hydraulic fracture tests are not generally undertaken but the leak-off test (LOT) is somewhat similar in procedure to the initial stages of a hydraulic fracture test and is routinely conducted during petroleum drilling. Leak-off tests are conducted to determine the maximum fluid density that can be used in the next drilling section (i.e. fracture gradient) and not for stress determination per se. During a LOT the pressure is increased until a decrease in the rate of pressurization is observed. Consequently the induced fracture is comparatively small compared to that induced during a hydraulic fracture test, resulting in fracture closure not generally being observed. However, Breckels and van Eeklen (1982) showed that leak-off test pressures provide an estimate of the Shmin, but not as 4 accurate an estimate as that yielded by hydraulic fracture tests. Recognizing the similarity between LOTs and hydraulic fracture tests, Kunze and Steiger (1991) proposed the Extended Leak-Off Test (XLOT). This test uses the same equipment as a LOT, but a procedure more similar to the hydraulic fracture test, with multiple cycles of pressurization and de-pressurization, results in a pressure versus time record that can be used to determine the Shmin with increased confidence. The orientation of the maximum horizontal stress may be determined by observing the orientation of the induced fracture using an impression packer or a borehole imaging tool (Engelder, 1993; Haimson, 1993). The magnitude of the maximum horizontal stress can be determined from XLOTs and hydraulic fracture tests in some circumstances where a re-opening pressure can be interpreted (Haimson and Fairhurst, 1967; Enever et al., 1996, etc.). With the improvements of wellbore imaging tools, borehole breakouts BOs and/or DITFs can be more accurately interpreted and their geometry observed. Zoback et al. (1985) proposed a method for determining the magnitude of the maximum horizontal stress using the angular width of breakouts around the wellbore is proposed. This technique was used to obtain SHmax in New Mexico (Barton et al., 1988). However, this technique is controversial because attempts to relate size and shape of breakouts to stress magnitudes requiring consideration of the geometrical effects of breakout development and the failure mechanisms of the material (Detournay and Roegiers, 1986, etc.). Nonetheless if breakouts are observed and compressive rock strength measurements available, a lower bound for SHmax can be determined (Moos and Zoback, 1990, etc.). Like breakout occurrence, DITF occurrence can be used to constrain SHmax, in this instance given knowledge of tensile rock strength (Moos and Zoback, 1990, etc.). Tensile rock strength is typically low compared to compressive rock strength and rocks typically contain planes of weakness on which the tensile rock strength is negligible. Consequently the tensile rock strength can be assumed to be negligible (Brudy and Zoback, 1999). 5 Widespread application of deviated drilling led to new techniques being utilized for stress determination. Aadnoy (1990) proposed a method for inverting three or more LOTs from wellbores of different trajectories to determine the complete stress tensor. Gjønnes et al. (1998) suggested the original method was inaccurate, because it ignored shear stresses, and proposed an improved method. However, the improved inversion also contained large uncertainties, in part due to the inaccuracy of LOTs and suggested the use of multiple techniques to determine the in situ stresses. Image logging in deviated wells led to the observation that breakout orientations rotate as deviation increases, depending on the stress regime and borehole azimuth (Mastin, 1988). A technique for inverting the variation in breakout orientations with borehole deviation and azimuth to determine the complete stress tensor is proposed (Qian and Pedersen, 1991). Peska and Zoback (1995) developed a similar technique for using rotation of breakout azimuths with deviation to constrain the stress tensor. However, the rotation of DITF azimuths and variations in the occurrence of both breakouts and DITFs are considered to constrain the full in-situ stress tensor. Using observations of both DITFs and BOs occurrence and change in orientation, the full in-situ stress tensor can be determined from a single deviated borehole. Besides the frictional failure provides a theoretical limit to the ratio of the maximum to minimum effective stress beyond which failure of optimally-oriented pre-existing faults occurs (Sibson, 1974). A large number of in situ stress measurements in seismically active regions have shown stresses to be at frictional limit (McGarr, 1980; Zoback and Healy, 1984). Where one or more of the stress magnitudes are known, frictional limits can be used to constrain stress magnitudes in seismically inactive regions and estimate stress magnitudes in seismically active regions. Most commonly SV and Shmin are known and the frictional limit is used to provide an upper limit to SHmax. 6