Minimum Horizontal Compressive Stress Research Articles

Structure and emplacement of the Coastal Deccan tholeiitic dyke swarm in Goa, on the western Indian rifted margin

Mafic dyke swarms, when controlled by a regional stress field, are emplaced perpendicular to the minimum principal compressive stress direction. However, mafic dyke swarms may also exploit pre-existing structural fabric in their host rocks. Distinguishing between the two scenarios is important for correct geodynamic understanding of magmatic events. Continental flood basalt provinces such as the Deccan Traps of India represent huge fissure eruptions produced by swarms of mafic dykes. The Coastal dyke swarm of the Deccan, along the western Indian rifted margin, is one of its three major dyke swarms. We present a field study of the Goa dykes, part of the Coastal swarm. The dykes are typical dolerites and basalts exposed in Proterozoic-age basement; lava flows which these dykes may have once fed have been stripped away by erosion, though exposed in the Western Ghats escarpment ~ 100 km to the east. The Goa dyke swarm contains 60 dykes, some of which form larger multiple-injection dykes. The dykes are short compared to typical (kilometers or tens of kilometers long) dykes in flood basalt provinces such as the Deccan or Iceland, and range in length from ~ 15 to ~ 220 m and in thickness from 3 cm to 20 m. Most dykes are vertical and the others dip steeply in various directions. Their structural attributes and internal features (such as vesicular zones and columnar jointing) provide clues to the processes of magma flow and solidification in the dykes. Field measurements yield an average crustal dilation of 8% due to dyke emplacement. Calculations of magmatic overpressures and magma chamber depths generally yield unrealistic values owing to the low aspect ratios of the dykes. Based on comparisons between the dyke trends and the host rock joint trends, we consider that a few of the Goa dykes were emplaced along pre-existing fractures, but the orientations of the great majority of the dykes reflect contemporaneous stress fields. Based on crosscutting relationships, we infer that the regional minimum horizontal compressive stress (σ3) changed over time from a ~E-W orientation to a ~NE-SW orientation and finally to a ~N-S direction.

Source characteristics and b-values of the Tuz Gölü Fault Zone in Central Anatolia, Turkey

We investigate significant earthquake sequences in the observation period between 2000 and 2018 along the Tuz Gölü Fault Zone in Central Anatolia. These sequences include a series of strong events with moment magnitudes (Mw) >5.0, e.g. 30 July 2005 Bala-Ankara Mw 5.2, 20 December 2007 Bala-Ankara Mw 5.7 and 26 December 2007 Mw 5.6 Afşar-Ankara earthquakes. The mainshocks are shallow focus strike-slip events with minor normal component at depths of 12–15 km. Focal depths of aftershocks range from 2 to 30 km. The focal mechanisms of the aftershocks are mainly normal faulting with variable strike-slip components. The geometry of focal mechanisms reveals a normal faulting regime with E-W and also NE-SW trending directions of T-axis in the entire activated region. A stress tensor inversion of focal mechanism data is performed to acquire a more accurate picture of the Tuz Gölü Fault Zone stress field. The stress tensor inversion results display a predominant normal stress regime with a NNE–SSW oriented maximum horizontal compressive stress (SH). According to high-resolution hypocenter relocations of the Tuz Gölü Fault Zone seismic sequences, eight clusters are revealed. The aftershock activities in the observation period between 5 March 2000 and 2 June 2018 extend from NW to SE direction. Seismic cross-sections show that a complex pattern of the hypocenter distribution with the activation of Tuz Gölü Fault Zone segments. The western clusters are associated with a fault plane trending mainly N-S and dipping towards almost vertical, while the eastern clusters are related to a fault plane trending NW and dipping towards SE direction. The best constrained focal depths are mainly confined in the crust (depth < 30 km) and range from 2 to 30 km. In this study, we compare the results of an analysis of b-values from seismicity and stress tensors of focal mechanism solutions to understand their coupling in terms of faulting and earthquake hazard implications. In particular, this comparison allows to investigate the spatiotemporal correlation between b-values and stress distributions and it is therefore able to locate fault segments that have a high potential of generating large earthquakes. According to recent seismicity, b-values range from 0.5 to 1.5 along the Tuz Gölü Fault Zone in Central Anatolia. The maximum horizontal compressive stress (SH) indicates N-S and NE-SW directions while the minimum horizontal compressive stress (Sh) displays E-W. These results represent that low stress variances are correlated with high b-values. Low b-values are predominant in areas with high stress rates, consistent with a high heterogeneity of focal mechanisms.

Analysis of the stress field in the DeSoto canyon Salt Basin for ensuring safe offshore carbon storage

Offshore geologic CO2 storage offers an attractive option to reduce greenhouse gas emissions. Vast CO2 storage capacity exists in Cretaceous-Neogene sandstone in the DeSoto Canyon Salt Basin. Understanding the stress and pressure regimes in the basin can help evaluate the geomechanical integrity of the formations, thus minimizing the risk of CO2 migrating out of the storage complex. Borehole breakouts were identified using four-arm dipmeter logs. Elongation of the breakouts is aligned with the minimum horizontal compressive stress (Shmin), which tends to be oriented northeast-southwest. Vertical reservoir stresses are influenced by rock and fluid density. Lithostatic and hydrostatic stress each have a power-law relationship to depth. The average lithostatic stress (Sv) gradient is ∼21.4 kPa/m. Hydrostatic pressure gradient increases with brine density to a maximum of ∼12.2 kPa/m. Geometric mean of the Shmin-depth values correspond to an effective Shmin - effective Sv quotient of ∼0.5. Injection pressure can be maintained safely below the estimated effective minimum horizontal stress, thereby reducing the risk of cross-formational flow. Future study should focus on further constraint of geomechanical properties, reservoir integrity, and seal integrity.

Crustal stress field in Yunnan: implication for crust-mantle coupling

We applied the gCAP algorithm to determine 239 focal mechanism solutions $$\left( {3.0 \le M_{\text{W}} \le 6.0} \right)$$ with records of dense ChinArray stations deployed in Yunnan, and then inverted 686 focal mechanisms (including 447 previous results) for the regional crustal stress field with a damped linear inversion. The results indicate dominantly strike-slip environment in Yunnan as both the maximum (σ 1) and minimum (σ 3) principal stress axes are sub-horizontal. We further calculated the horizontal stress orientations (i.e., maximum and minimum horizontal compressive stress axes: S H and S h, respectively) accordingly and found an abrupt change near ~26°N. To the north, S H aligns NW-SE to nearly E-W while S h aligns nearly N-S. In contrast, to the south, both S H and S h rotate laterally and show dominantly fan-shaped patterns. The minimum horizontal stress (i.e., maximum strain axis) S h rotates from NW-SE to the west of Tengchong volcano gradually to nearly E-W in west Yunnan, and further to NE-SW in the South China block in the east. The crustal strain field is consistent with the upper mantle strain field indicated by shear-wave splitting observations in Yunnan but not in other regions. Therefore, the crust and upper mantle in Yunnan are coupled and suffering vertically coherent pure-shear deformation in the lithosphere.

Structure and emplacement of the Nandurbar–Dhule mafic dyke swarm, Deccan Traps, and the tectonomagmatic evolution of flood basalts

Flood basalts, such as the Deccan Traps of India, represent huge, typically fissure-fed volcanic provinces. We discuss the structural attributes and emplacement mechanics of a large, linear, tholeiitic dyke swarm exposed in the Nandurbar–Dhule area of the Deccan province. The swarm contains 210 dykes of dolerite and basalt >1 km in length, exposed over an area of 14,500 km2. The dykes intrude an exclusively basaltic lava pile, largely composed of highly weathered and zeolitized compound pahoehoe flows. The dykes range in length from <1 km to 79 km, and in thickness from 3 to 62 m. Almost all dykes are vertical, with the others nearly so. They show a strong preferred orientation, with a mean strike of N88°. Because they are not emplaced along faults or fractures, they indicate the regional minimum horizontal compressive stress (σ 3) to have been aligned ~N–S during swarm emplacement. The dykes have a negative power law length distribution but an irregular thickness distribution; the latter is uncommon among the other dyke swarms described worldwide. Dyke length is not correlated with dyke width. Using the aspect ratios (length/thickness) of several dykes, we calculate magmatic overpressures required for dyke emplacement, and depths to source magma chambers that are consistent with results of previous petrological and gravity modelling. The anomalously high source depths calculated for a few dykes may be an artifact of underestimated aspect ratios due to incomplete along-strike exposure. However, thermal erosion is a mechanism that can also explain this. Whereas several of the Nandurbar–Dhule dykes may be vertically injected dykes from shallow magma chambers, others, particularly the long ones, must have been formed by lateral injection from such chambers. The larger dykes could well have fed substantial (≥1,000 km3) and quickly emplaced (a few years) flood basalt lava flows. This work highlights some interesting and significant similarities, and contrasts, between the Nandurbar–Dhule dyke swarm and regional tholeiitic dyke swarms in Iceland, Sudan, and elsewhere.

Elliptical calderas in active tectonic settings: an experimental approach

Caldera volcanoes form due to collapse of a magma chamber roof into the underlying magma chamber. Many field, theoretical and experimental studies have postulated that calderas are delimited by reverse ring faults and are surrounded by peripheral concentric normal faults. In the simplest theoretical scenario, circular magma chambers produce circular calderas. Many calderas, however, are elliptical in shape, particularly those in extensional and compressive tectonic settings. Several factors may explain elliptical calderas. The first is the presence of an elliptical magma chamber, established by, for instance, preferential intrusion along pre-existing basement structures or differential spalling of the magma chamber walls. The second is the overlap (nesting) of several discrete calderas to form a single, larger elliptical structure. The third is asymmetric subsidence. The fourth is variable pre-collapse topography. A fifth possible factor is distortion of the caldera faults by the regional stress field during caldera formation. A sixth factor is the post-collapse distortion of the caldera structure due to continued regional deformation. To better understand relationships between caldera surface expression, reservoir geometry and regional tectonic stresses, we conducted scaled analogue experiments. These experiments examined the impact of regional stress and associated structures on calderas formed during evacuation of reservoirs (circular rubber balloons) of known dimensions and depths. The results show that, in principle, calderas produced in compression/extension experiments are elongated parallel to the direction of minimum horizontal compressive stress, despite the chamber beneath being circular in plan view. As a consequence, model ring fault orientation varied from steeply dipping where striking perpendicular to the minimum horizontal regional compressive stress, to shallower dips where striking parallel to the minimum horizontal regional compressive stress. This leads us to suggest that the influence of a regional stress field on caldera fault orientation during and/or after caldera formation may be significant in the development of elliptical calderas. In addition, such variation of caldera ring fault dip from steep to relatively shallow could influence location and behaviour of ring fissure eruptions.

Seismic anisotropy in the shallow crust of the Loma Prieta segment of the San Andreas Fault System

We study seismic anisotropy beneath the Santa Cruz Mountains using digital recordings of S waves from 60 aftershocks of the 1989 Loma Prieta earthquake (Mω = 7.0) recorded at 18 local stations. Three‐component particle motion covariance matrix decomposition combined with a cross‐correlation method is used to estimate the polarization direction of the fast shear wave arrival and the delay time between the split shear waves. Results from this procedure are compared with those obtained through visual inspection of horizontal particle motions. Inclusion of the vertical component in the particle motion analysis allows the recognition and elimination of S to P converted phases from our study. Uncertainties in the polarization of the fast shear wave and in the delay time between arrival of the fast and slow waves are estimated to be about 20° and 10 ms, respectively. About half of the S wave records examined show clear evidence of shear wave splitting. Two persistent polarization directions of fast shear wave arrivals are observed regardless of the focal mechanism and hypocenter location of the individual events; 52% of the polarizations are parallel to the strike of the San Andreas fault (NW‐SE), and 24% are parallel to the probable direction of local maximum horizontal compressive stress (NE‐SW). The fault‐parallel fast polarization direction dominates at 10 stations and may result from mineral or fracture alignment caused by shearing along the plate boundary. The fast polarization direction perpendicular to the local axes of minimum horizontal compressive stress dominates at one station farthest from the San Andreas fault and is consistent with the hypothesis of extensive dilatancy anisotropy (EDA), where parallel alignment of fluid‐filled fractures produces the anisotropy. The predominance of fault‐parallel fast shear wave polarizations indicates that the use of shear wave splitting results to deduce the orientation of local axes of principal stress may not always yield accurate results. The splitting time between fast and slow shear waves varies from 10 to 125 ms and shows no systematic relationship with either hypocentral distance or focal depth. This suggests that the seismic anisotropy is no deeper than 2 km, the depth of the shallowest earthquakes analyzed. For an anisotropic zone 2 km thick, the average velocity anisotropy is about 5% in our study region.

The Contemporary Stress Field of the Barrow-Dampier Sub-Basin and Its Implications for Horizontal Drilling

The interpretation of borehole breakouts suggests that minimum horizontal stress (sh) is regionally oriented approximately N-S in the Barrow-Dampier Sub-Basin. More locally, breakout interpretation suggests that sh orientation is 005°?010° in the Wanaea/Cossack area, and 012°?022° in the Griffin/Chinook/Scindian area. Horizontal stress magnitudes in the Wanaea/Cossack area, derived from modified leak-off tests, together with vertical stress magnitudes derived from density and sonic log data, suggest that the stress (fault) regime in the Wanaea/Cossack area is on the boundary of extension (normal faulting) and strike-slip. The contemporary stress field impacts on planning the drilling direction of deviated and horizontal wells through the issues of mechanical wellbore stability and fracture intersection. In order to maximise intersection with any open, natural fractures, and to optimise any hydraulic fracturing program, wellbores should be horizontal and parallel to ah (minimum horizontal compressive stress) in the extensional (normal fault) and strike-slip stress regimes, and vertical in the compres-sional (reverse fault) regime. In order to minimise the tendency for borehole breakout, the stress anisotropy around the wellbore should be minimised ? i.e. horizontal wells should be drilled in the direction of sh in the extensional regime, and in the direction of sH (maximum horizontal compressive stress) in the compressional regime. In the strike-slip regime, horizontal wells can be oriented such that they are not subject to any stess anisotropy by progressively changing from the sh direction towards the sH direction as the horizontal stresses increase with respect to the vertical. In the Wanaea/Cossack area, wells drilled towards 005°-010° or 185°?190° will maximise the potential for intersection with open, natural fractures (should they be present), and recovery from any induced, hydraulic fracturing will be optimised. Furthermore, wells in this direction will be subject to the minimum stress anisotropy, and are thus least likely to be subject to breakout.

中・西部日本の地殻応力

We compiled data on the direction of the crustal stress measured in-situ and estimated from shallow (depth≤35km) earthquake focal mechanisms in the central and western parts of Honshu. In the central part of Honshu, the stress data were compiled by Tsukahara and Ikeda in 1991. This report summarizes the stress state in a rather large area: the central and western parts of Honshu. The results are as follows. (1) The stress state estimated from the stress direction and the type of faulting in and around the Izu Peninsula are explained in terms of dynamic interaction between the Philippine Sea (PHS) plate and the Asian (ASA) plate. (2) In the central part of the Kanto plain and the Kanto mountains, the minimum horizontal compressive stress (SHmin) is equal to or smaller than the vertical stress (i. e., tensile stress), and the azimuthal direction is roughly east-west. This stress condition cannot be explained by the westward movement of the Pacific (PAC) plate or the northwestward movement of the PHS plate against the ASA plate. (3) In the areas of the northern part of Kanto, Shin'etsu, Gifu, Hokuriku, and Chugoku, the azimuthal direction of the maximum horizontal compressive stress (SHmax) is west-northwest=east-southeast. Although this direction is approximately the same as that of the movement of the PAC plate, the stress state in these areas is not attributed to the plate movement because (a) some provinces with quite different stress directions lie between the PAC plate and these areas, and (b) SHmin in these areas is tensile stress. It seems that the stress state of this area is dominated by a large scale crustal movement of the Japan Sea or Eastern Asia. (4) In the area of Lake Biwa to Osaka, the stress state is slightly different from that in the areas discussed in (3), i. e., (a) the azimuth of the SHmax direction is approximately east-west, and (b) the type of faulting is different. There are strike-slip and reverse faults as opposed to strike-slip faulting alone for the surrounding area. The reason why this area has its own unique characteristics is not yet understood. (5) In the central Shikoku region, the azimuth of the SHmax direction is approximately east-west and the stress state regime is of the strike-slip faulting type. The east to west SHmax azimuth agrees well with the maximum shortening direction obtained from geodetic surveys in the region during these 100 years, which is attributable to the large crustal deformation at the Nankai Earthquake (1946, M=8.1). In contrast, however, the maximum shortening direction after the earthquake has been north to south. Therefore, the east-west SHmaxazimuth will change to north-south in the future.

Hydraulic Fracture Propagation in Layered Rock: Experimental Studies of Fracture Containment

Abstract Fracture geometry is an important concern in the design of a massive hydraulic fracture for improved natural gas recovery from low-permeability reservoirs. Determination of the extent of vertical fracture growth and containment in layered rock, a priori, requires an improved understanding of the parameters that may control fracture growth across layer interfaces. We have conducted laboratory hydraulic fracture experiments and elastic finite element studies that show that at least two distinct geologic conditions can inhibit or contain the vertical growth of hydraulic fractures in layered rock: (1) a weak interfacial shear strength of the layers and (2) an increase in the minimum horizontal compressive stress in the bounding layer. The second condition is more important and more likely to occur at depth. Differences in elastic properties within a layered rock mass may be important—not as a containment barrier per se, but in the manner in which variations in elastic properties affect the vertical distribution of the minimum horizontal stress magnitude. These results suggest that improved fracture treatment designs and an assessment of the potential success of stimulations in low-permeability reservoirs can be made by determining the in-situ stress state in the producing interval and bounding formations before stimulation. If the bounding formations have a higher minimum horizontal stress, then one can optimize the fracture treatment and maximize the ratio of productive formation fracture area to volume of fluid pumped by limiting bottomhole pressures to that of the bounding formation.

Analysis of factors influencing fracture initiation and orientation in oil reservoir sandstone : Komar, CA Frohne, KH 11F. US Bur. Mines, RI 7813, 1973, 22P

Hydraulic fracturing has developed into a widely applied technique for increasing production from petroleum and natural gas reservoirs. Although more than a million wells have been fractured, the degree of understanding of the mechanics of hydraulic fracturing is still incomplete. Laboratory-scale hydraulic fracture tests were conducted on directionally oriented sandstone material, along with measurements of directional rock properties such as tensile strength, permeability, ultrasonic velocity, and dynamic elastic constants. Fracture orientation was determined as a function of various combinations of stress, rock saturation, rate of borehole pressurization, and direction of minimum tensile strength relative to minimum horizontal compressive stress. The objective was to investigate whether horizontal stresses always controlled the orientation of induced vertical hydraulic fractures, or if under conditions of small differences in stress and/or slow borehole pressurization rates, the induced fracture direction was influenced by directional properties of the rock matrix. This study shows that the expected influence of horizontal earth stress on the orientation of an induced hydraulic fracture becomes negligible whenever the magnitude of the difference between the compressive stresses is 200 psi or less. When this occurs, fracture orientation is controlled by the directional properties of the rock--primarily permeability and tensile strength. (auth)

Factors controlling fracture orientation in sandstone : 48th Ann. Fall Meeting Soc. Petrol. Engng. AIME, Las Vegas, Sept.-Oct. 1973 AIME,SPE PREPRINT 4567,1973,8P

Laboratory-scaled hydraulic fracture tests were conducted on directionally oriented sandstone material, along with measurements of directional rock properties such as tensile strength, permeability, sonic velocity, and dynamic elastic constants. In these tests, fracture orientation was determined as a function of various combinations of stress, rock saturation, rate of borehole pressurization, and direction of minimum tensile strength relative to minimum horizontal compressive stress. The objective of the experiment was to investigate whether horizontal stresses always controlled the orientation of induced vertical hydraulic fractures, or if, under conditions of small differences in stress and/or slow borehole pressurization rates, the induced fracture direction was influenced by directional properties of the rock matrix. This study shows that the expected influence of horizontal earth stress on the orientation of an induced hydraulic fracture becomes negligible whenever the magnitude of the difference between the compressive stresses is 200 psi or less. When this occurs, fracture orientation is controlled by the directional properties of the rock--primarily permeability and tensile strength.