Direction Of Horizontal Stress Research Articles

Hydraulic fractures simulation in non-uniform stress field of horizontal shale gas well

Shale reservoirs have low porosity and ultra-low permeability. A significant increase in gas well production requires horizontal well fracturing. In this view, the propagation behavior of hydraulic fractures during the fracturing process is critical to the effect of shale gas reservoir stimulation. However, some shale formations have developed faults and the in-situ stress field has a non-uniform distribution. Also, the maximum horizontal principal stress direction varies with the spatial position, and non-planar deflection propagation behavior in hydraulic fractures is possible. The purpose of this article is to reveal the effect of the development of faults in the shale formation on the propagation of hydraulic fractures. A calculation model for the non-uniform tectonic stress field near the fault was established, and on this basis, we constructed a shale gas horizontal well-staged multi-cluster fracturing hydraulic fracture deflection propagation model under the influence of faults. Furthermore, the fracture propagation law was simulated and analyzed in the presence of a non-uniform in-situ stress field. The findings demonstrate that hydraulic fractures near the strike-slip fault tend to run parallel to the fault direction, whereas hydraulic fractures near the normal fault tend to run perpendicular to the fault direction. The greater the fault throw and the greater the hydraulic fracture propagation deflection angle, the closer the hydraulic fracture is to the fault. The deflection behavior of hydraulic fractures increases flow resistance in the fracture, and proppant transport does not flow smoothly, increasing the difficulty and risk of the fracturing operation. The findings of this study could provide an important theoretical foundation for the design of staged multi-cluster fracturing of horizontal wells near faults in shale formations.

A Random‐XFEM technique modeling of hydraulic fracture interaction with natural void

In this paper, a Random-XFEM technology was employed to simulate hydraulic fracture interaction with the natural void in a random field of Young's modulus. The random distribution of Young's modulus is characterized by random field theory, while the stress and pressure fields fracturing were solved by the extended finite element method. And a Random-XFEM iteration algorithm was proposed to solve the hydraulic fracture propagation problem. Then the proposed model was verified against the KGD model and numerical study. A series of numerical examples were presented to analyze the interaction mechanism of hydraulic fracture and void in a random field. The numerical results show that the random field of Young's modulus has a great impact on the hydraulic fracture propagation path. Under the random distribution of Young's modulus, the hydraulic fracture would deviate from the direction of maximum horizontal principal stress. And the random field parameters (Young's modulus mean and point variance) have different effects on the hydraulic fracture propagation path. Also, the interaction patterns of hydraulic fracture and void are greatly affected by random fields.

Upper crustal anisotropy in the Southeastern Sichuan Basin, China from shear-wave splitting measurements

The Sichuan basin which embodies salt and shale gas resources, is characterized by low seismicity. Seismicity in the southeastern Sichuan basin increased dramatically in recent years, including a series of moderate to strong earthquakes. We investigate seismic anisotropy in the upper crust by performing shear wave splitting analyses on local earthquakes recorded at seventeen stations around the Changning-Xingwen area, southeastern Sichuan basin between January 2016–February 2021. We perform an automatic shear wave splitting analysis and obtain 2926 high-quality splitting measurements by examining 5174 local earthquakes. The delay times range between 0.08 and 0.20 s, and the anisotropy magnitude ranges between 1.9% and 5.5% with a mean of 4.2%, indicating that the study area has significant strength of anisotropy. The fast polarization directions are highly variable reflecting a combined effect of complex local structure and stress field in this area. In the southeastern part of the study area, fast directions are aligned parallel to NW- and NE-oriented surface structures, suggesting structural anisotropy. In the northwestern part of the study area, fast-polarization directions align parallel to the strike of folds and the direction of maximum horizontal compressive stress, probably reflecting the combination of both stress- and structural-controlled anisotropy. Whereas at these stations of central part, fast directions tend to align parallel to the direction of maximum horizontal compressive stress, suggesting stress-induced anisotropy. We examined the temporal variation of seismic anisotropy associated with the 2019 MS 6.0 Changning earthquake. The significant changes in splitting parameters during the Changning earthquake period may only reflect the spatial changes in seismic anisotropy.

Characterization Of Naturally Fractured Basement Reservoir And Its Play Concept, South Pattani Basin, Gulf Of Thailand

Structural development and complex basin forming mechanism in Pattani Basin may have formed naturally fractured basement reservoirs. The basement of the South Pattani Basin is poorly understood, as a result of low seismic resolution in its deeper part and lack of wells that reach the basement. Hence, seismic interpretation may improve the understanding of South Pattani Basin basement fracture systems. This paper aims to investigate the geological and seismic characteristics of the fractured basement reservoir, identify the relation between basin evolution and fracture network and development, and proposed a play concept for naturally fractured basement reservoir. Seismic attributes exhibit prominent N-S fault and fracture trends in the study area. Three basement high areas revealed that open fractures distribution identified using seismic ant-tracking technology has good correlation with regional maximum horizontal stress direction (N-S), but the intra-basement (central) area exhibits strong alignment with pre-existing fabrics (NW-SE). Open fracture networks in Zone A and B developed around major fault swarm features. Integrated qualitative and quantitative seismic analysis suggests that the three basement high areas have the potential for fractured basement reservoirs, with a complex fracture configuration and development due to poly-phase deformations.

Distribution Law of Deep Complex In Situ Stress and Influence of Underground Engineering in Huanghuai Area

Huanghuai area is rich in coal resources, but due to the increasingly complex geological environment faced by coal mining, the complexity of structural stress is one of the main problems. In order to find out the distribution law of deep in situ stress in the Huanghuai area, the in situ stress measurement data of 81 effective measuring points in 24 mines with depths ranging from −100 m to −1200 m are analyzed in the present study base on the in situ stress measurement data. Furthermore, numerical simulation and field observation are used to analyze the deformation and failure characteristics of the surrounding rock. The research results show that the deep mining area of Huanghuai exhibited a high stress level, and the vertical and horizontal principal stress increases with increasing depth. The ratio of the lateral pressure coefficient ranges from 0.90 to 2.70, and the in situ stress field presented a trend of transition to the quasihydrostatic pressure field type as the depth extended, in which 80.23% of the measuring points are distributed between 1.20 and 2.10, belonging to the typical tectonic stress field type in which tectonic stress is absolutely dominant. The observation results of the surrounding rock and numerical simulation reveal that when the layout axis of the roadway is approximately perpendicular to the direction of the maximum horizontal principal stress, a high stress concentration area is present on the roof and floor of the roadway, the deformation increases sharply, and the support pressure of the roof and floor increases.

A Three-Dimensional Finite-Element Model in ABAQUS to Analyze Wellbore Instability and Determine Mud Weight Window

Wellbore instability is one of the main problems of the oil industry, causing high costs in the drilling operation. Knowing about the mechanical properties of involved formations and in-situ stresses is a privilege gained by determining an appropriate mud weight window (MWW). To this aim, a three-dimensional (3D) finite-element model was simulated in ABAQUS to analyze in-situ stresses and determine the MWW in the drilling operation of wellbore-D in the Azar oilfield. The results from the 3D finite model revealed that the Azar oilfield is structurally under the impact of a complex tectonic system dominated by two reverse faults with a configuration of σH > σh > σv across the Sarvak Formation. The amount of vertical, minimum, and maximum horizontal stresses was 90.15, 90.15, and 94.66 MPa, respectively, at a depth of 4 km. Besides, the amount of pore pressure and its gradient was 46 MPa and 11.5 MPa/km, respectively. From drilling wellbore-D in the direction of the maximum horizontal stress, the lower limit of the MWW was obtained at 89 pcf. In this case, the results showed that the wellbore with a deviation angle of 10° is critical with a mud weight lower than 89 pcf. It caused the fall of the wellbore wall within the plastic zone sooner than other deviation angles. Also, in the case of drilling wellbore in the direction of minimum horizontal stress, the lower limit of the MWW was 90.3 pcf. Moreover, in the deviation angle of approximately 90°, the wellbore wall remained critical while the mud weight was below 90.3 pcf. Comparison of the results of numerical and analytical modeling showed that the modeling error falls within an acceptable value of < 4%. As a result, the wellbore with the azimuth of the maximum horizontal stress needed less mud weight and decreased the drilling costs. This particular research finding also provides insights for obtaining the lower limit of the mud weight window and determining the optimal path of the well-bore when using directional drilling technology.

Estimation of the optimal direction of the horizontal borehole relative to the minimum and maximum formation stress

The article discusses the analysis and assessment of the optimal direction of the horizontal wellbore and its spatial location relative to the minimum and maximum reservoir stresses play a significant role in the design of an operation to create multiple hydraulic fractures. Theoretically, two cases are possible: the horizontal wellbore is located strictly in the direction of maximum horizontal stress; the horizontal wellbore is located strictly in the direction of the minimum horizontal stress. As a conclusion based on the hydraulic fracturing design, the well productivity factor was calculated and compared for longitudinal and transverse fractures; longitudinal fractures have a clear advantage. According to the presented calculation, the hydraulic fracturing method will have advantages in a horizontal well in a highly permeable reservoir. The hydraulic fracturing method will increase the vertical permeability. According to the presented calculation, the hydraulic fracturing method will have advantages in a horizontal well in a highly permeable reservoir. The hydraulic fracturing method will increase the vertical permeability and unite the disparate parts of the reservoir. The hydraulic fracturing method will increase the vertical permeability and unite the disparate parts of the reservoir, which will make it possible to more efficiently develop the reserves of the Neocomian deposits in the field.

3D Modelling of Excavation-Induced Anisotropic Responses of Deep Drifts at the Meuse/Haute-Marne URL

Understanding the excavation-induced fractured zone (EFZ) around drifts is paramount in the context of the deep geological disposal for nuclear waste since fractures can introduce pathways for the migration of radionuclides. Drifts in the Meuse/Haute-Marne Underground Research Laboratory (URL) have been essentially excavated following the two main directions of major and minor horizontal stresses. Field observations on the two drifts GCS (parallel to major horizontal stress direction) and GED (parallel to minor horizontal stress direction) in the URL show anisotropic shapes of EFZ around drifts through both orientations and anisotropic convergences. These anisotropic responses resulted from the inherent and/or induced anisotropies of the host rock as well as the anisotropic stress field. This study focuses on 3D numerical modelling of excavation-induced anisotropic responses including shape and extent of EFZ, and short-term convergences of drifts. The main assumption is that the failure of claystone material is due to fracturing along weakness planes (ubiquitous joints) and the failure of the rock matrix. The ubiquitous joint failure is represented by perfectly plastic models for both tensile and shear yield functions. Their orientation is determined from the stress state based on the fracture mechanics, which includes tensile, longitudinal splitting and shear (conjugate planes) cracks. The rock matrix is assumed to be elastoplastic with hardening, softening and residual behaviours. Confining pressure dependency for the post-peak behaviour with a brittle–ductile transition is taken into account for the rock matrix. The proposed model is implemented into a commercial numerical software FLAC3D. The main features of the implemented model are shown by the simulation of laboratory triaxial compression tests, as well as field observation within the URL. In particular, comparisons between 3D simulations of GCS and GED drifts with in situ observations shows promising results, which demonstrates advances of present model with respect to existing models.

Analysis of coseismic slip distributions and stress variations of the 2019 Mw 6.4 and 7.1 earthquakes in Ridgecrest, California

Exploring spatiotemporal variations in the regional stress field is critical for understanding the interactions between active tectonic plates. On July 4 and 6, 2019, strike-slip earthquakes of Mw 6.4 sinistral and 7.1 dextral, respectively, occurred in Ridgecrest, California, which provided an appropriate condition for studying conjugate earthquake stress variation. In this study, we used GNSS coseismic displacement to invert the coseismic slip distributions of each earthquake. According to the spatiotemporal distribution, the focal mechanisms were divided into three time periods and five subareas. Therefore, spatiotemporal variations of the stress field were calculated. Results indicate that the two earthquakes were not purely strike-slip, but had minor dip-slip components. The maximum slips of the Mw 6.4 foreshock and the Mw 7.1 mainshock were 0.7 and 3.1 m, respectively. Areas of significant stress variations corresponded to areas of larger slip distributions. During the three time periods, the maximum horizontal stress (SHmax) direction in each subarea first experienced counterclockwise and then clockwise rotation; the SHmax direction of the foreshock epicenter region changed from 3.8° to 2.8° to 5.8°. After the mainshock, the SHmax of the foreshock epicenter region rotated clockwise by ~3.0°, the deviatoric stress was ~4.5 MPa, and the stress drop in the epicenter region of the mainshock was ~4.3 MPa, from which we can judge that the stress was almost completely released. Six months before the earthquakes, the b value began to change markedly, while it stabilized after the earthquakes. In the dextral shear zone formed by the relative motions of the Pacific and North American plates, the cumulative stress tends to be jointly regulated by NW–SE and NE–SW oriented conjugate fractures. These two Ridgecrest earthquakes are a phenomenon of stress regulation.

Complexity of near-wellbore hydraulic fracture morphology around perforated wells with various orientations in tight reservoir

Horizontal wells with multiple perforated fracturing is main method to improve well production in the tight formation. However, hydraulic fracture morphology remains obscure because of different horizontal stress contrast, wellbore direction, and pump rate, resulting in no guidance for perforation parameters design. To uncover the mask, a perforated wellbore fracturing model is established based on the continuous damage theory, combing with field data to investigate the effects of above three factors on hydraulic fracture morphology around wellbore. The results indicate that induced fractures could overlap and interact with each other when the wellbore is set along the direction of minimum horizontal stress. The induced fractures have narrow width because of stress shadow effecting. However, when angle between wellbore and the minimum horizontal stress direction increases, the induced fractures prefer to link up as a simple one. Moreover, induced fractures could propagate along and perpendicular to the wellbore direction under a small horizontal stress contrast, forming a complex hydraulic fracture morphology. A high pump rate resists stress shadow effecting and improves hydraulic fracture volume, but cannot decrease the complexity of near-wellbore fractures under a small horizontal stress contrast.

Azimuthally Anisotropic Structure in the Crust and Uppermost Mantle in Central East China and Its Significance to Regional Deformation Around the Tan‐Lu Fault Zone

AbstractSeismic anisotropy can be linked to different mechanisms, structures, and sources. We constrained the 3‐D depth‐dependent shear wave speed isotropic and azimuthally anisotropic structures with Rayleigh wave phase velocity from ambient noise in central Eastern China. We compared the results with other models and found that in the upper crust, the maximum horizontal stress direction differs mainly from the anisotropy that coincides with the strikes of major faults and geologic structures. We inferred that the anisotropy within proximity of faults might be related to fault fabrics, including fractures that strike parallel to the fast axes. The Tan‐Lu Fault controls the anisotropy in the crust to the uppermost mantle. The direction of fast axes in the fault zone is NNE‐SSW to N‐S, coinciding with the fault strike and trend that matches the fault shape on the surface. Southeastern North China craton has a weak anisotropy in the crust and uppermost mantle. The sources are possibly connected to the thrusting, tight trending folds, and dipping thrusts observed to be sub‐parallel to the Dabie Orogenic Belt (DOB). We propose that the NNE‐SSW Zhangbaling uplift group comes from the extension and ductile shearing in the Tan‐Lu Fault zone and the dragging of the northeastern South China Craton in the crust and the uppermost mantle. The N‐S polarized fast axes in the lower crust and uppermost mantle across the Sulu orogen and Xuzhou thrust‐and‐fold belt are the products of the resultant effect of subduction and deep Tan‐Lu faulting.

Geomechanical Modeling and Inversion Analysis of the in-situ Stress Field in Deep Marine Shale Formations: A Case Study of the Longmaxi Formation, Dingshan Area, China

Based on the comprehensive analysis of wellbore characteristics in a deep shale gas field, the in-situ stress state of the shale reservoir was assessed in this study for the Longmaxi formation in the Dingshan area, Southwestern China. The data obtained from hydraulic fracturing, drilling-induced fractures, and in-situ core testing were used to determine the magnitude and direction of the maximum principal horizontal stress in five wells. Besides, hydraulic fracturing and cross-multipole array acoustic logging (XMAC) were employed to determine the vertical variation of the in-situ stress. Based on the logging interpretation and mechanical test results, the spatial distribution of rock mechanical parameters in the Dingshan area was assessed by the amplitude variation versus offset (AVO) seismic inversion. A 3D heterogeneous mechanical inversion model was realized via the ANSYS and CATIA3D finite element software packages, providing the area in-situ stress field simulation. The depth, fault strike, and position change effects on the main stress, horizontal stress difference, and horizontal stress difference coefficient were numerically simulated. The results show that the maximum principal stress azimuth was mainly concentrated in the NE20°-NE80° sector. Moreover, the development zone of natural fractures was related to the area with the highest principal stress differences. The maximum principal stress variation in the study area was mainly in the compressive range from −135 to −45 MPa, gradually increasing from east to west and south to north. The stress type mainly depended on the depth, fault strike, and rock mechanical parameters, while the stress difference and stress difference coefficient near the fault structure were relatively small. This study’s findings are considered instrumental in improving the borehole stability, determining the casing setting point, and optimizing the well location in deep shale reservoirs with similar geological conditions.

Depth-dependent crustal azimuthal anisotropy in the Salton Trough, southern California

We present new crustal models of azimuthally anisotropic P-wave velocity, isotropic P-wave velocity (Vp), isotropic S-wave velocity (Vs) and Vp/Vs ratio for the Salton Trough. High Vp/Vs ratio is revealed at depths of 2–8 km along the San Andreas Fault, implying the possible presence of fluids. High Vp and high Vp/Vs ratio (>1.8) structures of the mid-lower crust beneath the Salton Trough possibly reflect the underplated gabbroic rocks as a result of the extension-induced partial melting of the upwelling asthenospheric materials. The fast velocity directions (FVDs) generally correlate with the direction of the maximum horizontal compressive stress except that fault-parallel FVDs are found at main fault traces. However, the FVDs in the Salton Trough show complex features. The northern Slaton Trough basin (the northern Salton Sea basin and Coachella Valley basin) is dominated by NW-SE FVDs, which are possibly due to the active compression happening there. E-W oriented FVDs predominate the upper crust of the southern Salton Trough basin (the southern Salton Sea basin and Imperial Valley basin), possibly due to faulting and/or block rotation. As the depth increases (12–18 km), the FVDs to the south of the Salton Sea have an overall rotation and gradually become NW-SE. The depth-dependent variation of anisotropy orientation may be attributed to a large band of underlying heat source that probably causes a change of stress field by imposing thermal stress on overlying rocks. In all, our velocity models suggest that faults in the Salton Trough may bear a high risk of mechanical failures due to the complexities of stress distribution and geological structures as well as the presence of a large volume of fluids and heat.

Analysis of Crustal Stress and Its Influence on the Stability of the Deep Tunnel in the Huanaote Mining Area

Crustal stress is a critical parameter utilized to analyze the stability of the tunnel in underground hard‐rock mining sites. In order to analyze the distribution law of crustal stress and its influence on the stability of the deep tunnel in the Huanaote mining area, the in‐situ stress field model of this area was constructed firstly by using the borehole stress relief method. Moreover, the numerical model is established based on three real engineering conditions: the excavation direction is parallel, vertical, and intersection to the measured maximum horizontal principal stress direction, respectively. Results show that, compared with the other two layout schemes, the stress of two side walls reaches peak at 27 MPa, when the excavation direction is intersected to the measured maximum horizontal principal stress direction, which indicates that the support and maintenance of two side walls should be strengthened to ensure the stability of the tunnel and the safety of personnel and equipment in real projects.

Geologic aspects (faults, landslides and volcanic dikes) of the Nateekin River shallow earthquake swarm of 15 June 2020 near Makushin Volcano, Unalaska Island, Alaska, U.S.A.-siftdesk

Starting 15 June 2020, a shallow earthquake swarm occurred in the Nateekin River valley just east of Makushin Volcano of Unalaska Island, Alaska, U.S.A. Focal mechanism determinations were made on the larger earthquake events. These correlated with four known fault groups originally recognized during 1980-85 field work in this region. These are (a) numerous N 54° W ± striking normal faults, (b) prominent N 74° W ± striking normal faults, (c) N 50° E ± strike-slip faults, and (d) a N 36° E ± striking reverse faults. These fault groups correlate with known dikes for the region, which suggest magmatic intrusions are associated with this earthquake swarm. These faults reflect a predictable fault structure for a regional maximum horizontal tectonic stress direction of N 54° W ± with a localized spreading rift zone associated with Makushin Volcano that is striking N 74° W ±. This rift zone has a reactivated landslide and numerous nearby small landslides caused by this June/July earthquake swarm. This swarm sheds insight into the faulting, volcanic and geothermal processes of the region. Key words: Shallow earthquake swarm in a volcanic rift zone; four different seismic focal (fault) mechanisms recognized; associated active faults and landslides observed; related Holocene dikes and volcanic activity; regional maximum horizontal tectonic stress and magmatic processes; extensive geothermal resources.

Seismotectonics of the easternmost Cypriot Arc: An active plate boundary

The easternmost segment of the Cypriot Arc crosscuts the seabed between the Syrian and Cypriot coasts. This arc represents the plate boundary between the Anatolian plate and the Sinai subplate. The current study aims to analyze and integrate earthquake, tectonic, bathymetric and geophysical marine data of this segment for assessing its seismotectonic setting. Bathymetry of the studied area has provided a detailed chart of the seabed and permitted tracing of the main faults. The seismic activity has been characterized as moderate, where 306 earthquakes with mb ≥ 3.0 have been recorded during the period 1894–2017. The fault plane solutions have been examined in details for identifying the operative stress field. The focal mechanisms reveal that the thrust faulting events are dominant in the south of Cyprus; the strike-slip events appear eastward; and the normal faulting events are located in the northeast termination of the Cypriot Arc. This observation can be interpreted as an evident change of tectonic regime along both Latakia and Kythrea faults. Spatial variations of the maximum horizontal compression stress (SHmax) direction have been observed with relative conformity across the Cypriot Arc. These variations of the present-day stress field could be related to the northward movement of the Sinai subplate, whereas its various directions could be produced by a wavy complex plate boundary of the Cypriot Arc. The finding contributes to tsunami hazard assessment for the easternmost Mediterranean Sea.

Case study of hydraulic fracturing in an offshore carbonate oil reservoir

Maximizing petroleum production while efficiently managing the operational costs is the oil and gas industry's primary goal which requires innovative engineering approaches and production-enhancing treatments such as hydraulic fracturing (HF). During the HF process, the injected fluid mixed with sands or proppants will create permanent fluid channels to drain more of the reservoir volume. The level of complexity and various constraints involved in real field treatments have made HF even more challenging in layered carbonate reservoirs with the water drive mechanism. A prominent concern is the downward fracture growth to the oil/water contact zone that may cause unfavorable water cut levels. This fracture height confinement criterion necessitates optimization of fracture dimension design. Fracture height development is mainly a function of in-situ stress conditions and stress magnitude differences between geologic layers. In cases with a water table at the proximity of the wellbore, fracture height directly affects the operational success. This paper demonstrates a practical step-by-step approach towards the design of hydraulic fracturing treatment in an offshore carbonate oil reservoir. The modeling process involves optimization of the location, number, and conductivity of the proposed fractures. Injection of high viscosity fluid causes a bi-wing vertical planar fracture to propagate perpendicular to the direction of minimum horizontal stress in the strike-slip faulting regime. Dimensions of the induced hydraulic fractures are also impacted by the amount and type of proppants. However, as with this case study, the magnitude of vertical stress is in the same range as the maximum horizontal stress; the fracture height growth is the limiting factor. The LGR method is used to define fractures in the dynamic reservoir model which has been built based on a complete set of data ranging from the analyses of logs, core samples, and seismic details, to perform production forecasts and economic evaluation. Then a hydraulic fracture software is implemented to provide a timetable for fracturing fluid volume and mixing proppant concentration for the desired fracture dimensions. The results show that, despite the operator's previous perception, five hydraulic fractures per well would be economical, which include a 150 ft long fracture and four shorter fractures with an approximate length of 75 ft designed to manage the risk of penetration into the water-bearing formations. Due to the reservoir pressure drop by time and more flexible fracture dimension constraints at earlier stages of production, executing such stimulations earlier than later would improve the commercial outcomes.

Research on In Situ Stress Distribution of the Railway Tunnels in Southwest China Based on the Complete Temperature Compensation Technology

In situ stress is the natural stress existing in the stratum without engineering disturbance, also known as initial stress, absolute stress, or original rock stress. In order to master the in situ stress of the Manmushu Tunnel and Mamo Tunnel in Southwest China, the casing stress solution method is adopted in this paper. Through the combination of field measurement and laboratory test, the basic data such as initial strain during stress relief are collected, and the in situ stress values are analyzed in combination with indoor temperature compensation test, confining pressure calibration, and relevant rock mechanics tests. The measured results show the following: (1) the maximum horizontal principal stress σh.max ranges from 6.44 MPa to 19.74 MPa; the vertical principal stress σ v ranges from 4.11 MPa to 13.48 MPa; and the minimum horizontal principal stress ranges from 4.32 MPa to 11.22 MPa. (2) The maximum horizontal principal stress directions of the five measuring points are all located in the NW direction, which is basically consistent with the maximum principal stress direction of the regional tectonic stress field. The maximum horizontal principal stress (σh.max), the minimum horizontal principal stress (σh.min), and the vertical principal stress ( σ v ) all increase with the increase of buried depth, and the relationship is approximately linear. It is suggested that, in the actual construction process, the construction method and construction parameters should be optimized scientifically and reasonably to reduce the disturbance of blasting on the tunnel surrounding rock. After tunnel excavation, support measures should be taken quickly, timely, and scientifically to reduce and control the deformation of the surrounding rock.

Integrated Mechanical Earth Modeling for Predicting Sand Production: A Case Study

Summary Sand production is a serious problem in oil and gas wells, and one of the main concerns of production engineers. This problem can damage downhole equipment and surface production facilities. This study presents a sand production case and quantifies sanding risks for an oil field in Iraq. The study applies an integrated workflow of constructing 1D Mechanical Earth Modeling (MEM) and predicting the sand production with multiple criteria such as shear failure during drilling, B index, and critical bottomhole pressure (CBHP) or critical drawdown pressure (CDDP). Wireline log data were used to estimate the mechanical properties of the formations in the field. The predicted sand production propensity was validated based on the sand production history in the field. The interpretation results of some wells anticipated in this study showed that when a shear failure occurs during drilling, the B index is around 2 × 104 MPa or less and the CBHP is equal to the formation pore pressure. For this case, sand control shall be carried out in the initial stage of production. On the other hand, when the shear failure does not exist, the B index is always greater than 2 × 104 MPa, and the CBHP is mostly less than the formation pore pressure. In this case, implementing sand control methods could be postponed as the reservoir pressure undergoes depletion. However, for the anticipated field, sand control is recommended to be carried out in the initial stage of well production even when the CBHP is less than the formation pore pressure since sanding will be inevitable when the reservoir pressure depletes to values close to the initial reservoir pressure. The tentative evaluation of the stress regime showed that a normal fault could be the stress regime for the formations. For a normal fault stress regime, the study explained that when the reservoir permeability is isotropic, an openhole vertical wellbore has less propensity for sand production than a horizontal wellbore. Moreover, when the wellbore azimuth is in the direction of the minimum horizontal stress, the CBHP will be lower than in any other azimuth, and sanding will take place at higher wellbore inclination angles. For the anticipated field, because of the casedhole well completion and the anisotropic reservoir permeability, a horizontal well drilled in the direction of minimum horizontal stress with oriented perforation in the direction of maximum horizontal stress is an alternative method for controlling sand production.

In situ stress characteristics of the NE Sichuan basin based on acoustic emission test and imaging logging

This study presents the distribution rule of in situ stress in the northeast Sichuan basin and its relationship with fracture. Sixty-seven sets of core samples of 21 Wells from the terrigenous clastic rock formation (Shaximiao, Qianfoya, Xujiahe) and marine carbonate formation (Jialingjiang, Leikoupo, Feixianguan) in the northeast Sichuan basin were tested by acoustic emission experiment. The in situ stress variation with the depth was established and the corresponding regression analysis was done. The horizontal principal stress direction of terrigenous clastic rock formation and marine carbonate rock formation was obtained by combining the dual diameter data of 6 wells and the imaging logging data of 3 wells. The results show that the vertical stress in the northeast of Sichuan basin has a linear relationship with the depth, and there is little difference between the vertical stress and the overburden weight of rocks. The maximum and minimum horizontal principal stress and horizontal shear stress increase with the burial depth. The divergence degree of horizontal shear stress with depth greater than 3000 m is greater than that of the stratum smaller than 3000 m. The horizontal stress plays a dominant role in the northeast Sichuan basin. With the increase in depth, the influence of tectonic stress field decreases and the vertical stress increases. Impacted by Dabashan and Qinling plate tectonic movement, the direction of in situ stress in marine carbonate strata is nearly east–west. The direction of maximum horizontal principal stress in terrigenous clastic rock formation is basically northwest–southeast. The imaging logging data show that the fracture direction is consistent with the horizontal principal stress direction, and the present in situ stress direction is favorable to the secondary reconstruction of natural fractures, and the fractures keep good opening. The distribution law of in situ stress in northeast Sichuan basin shows σH > σV > σh, indicating that the fault activity in this area is dominated by strike-slip type, the tectonic stress field is dominated by horizontal tectonic stress, in addition that the stress state is conducive to reverse fault activity.