Stress State Of Rock Research Articles

Effect of nonuniform drill mud cake on stress state of reservoir rocks

The article describes simulation of stress state and pore pressure in a reservoir, in the vicinity of a horizontal well, subjected to the hydromechanical effect of drilling mud, using the poroelastic model of reservoir deformation, which accounts for the dynamics of the drill mud cake formation on the wellbore walls. It is illustrated how the stress and pore pressure are distributed when no cake is formed and in cases f the uniform-permeable and nonuniform-permeable cake.

Types of orebodies on the basis of the occurrence depth and stress state. Part II: Orebody tectonotypes and geomedium models

The author has accomplished systematization of ore fields by their geomechanical conditions based on the analysis of their tectonic structures. It is established that natural stress fields in the same type geological and tectonic structures are similar in mining regions worldwide. The author has distinguished four geomedium models differentiating the change of the rock stress state with increase in the rock occurrence depth.

The Tunnel of Small Interval Clip Rock Mechanics Properties Research

Abstract. In jiangxi red XiaShan highway tunnel interval for engineering background, the key research different scheme for tunnel construction process between them the mechanical behavior of rock and analyzed. For small interval double hole parallel tunnel between them the complex rock stress state, the finite element analysis software for using the numerical analysis method is buried deep in the condition of small interval period of bias by different construction scheme of tunnel numerical simulation. To meshshotcreting firstly method, CD method, up and down steps method, the construction method of different displacement and deformation of the stability of surrounding rock and the comparative analysis. Analyze the different schemes of before and after the surrounding rock tunnel excavation and supporting structure composed of each other of the unity displacement change rule. Put forward the tunnel between them weak rock the concept, more explicit the engineering geological conditions of weak rock tunnel clip to control surfaces. And on the basis of guidance for engineering construction, in actual construction which has obtained a better effect. The result is of a similar project design and construction to provide the reference and the model.

Stress state of rocks in subduction zone

The authors use the boundary element method in the 2D elastic problem to investigate the regularities of the principal stress distribution in the subduction of the oceanic plate under the continental plate under different boundary conditions. The investigation covers the cases when the fault zone has irregularities and the fault zone boundary is smooth. The point displacements at the boundaries of the continental and oceanic plates are analyzed. It is shown that the anticlimax induced by an instantaneous failure along the fault zone irregularities can generate an earthquake with M s = 7.5 and higher magnitude, with 2–7-meter shears of the oceanic and continental lithospheric plates.

Features of thermomechanical effects in rock salt samples under uniaxial compression

The article describes the uniaxial compression tests on rock salt samples under monotonic loading, which were carried out with the synchronous record of changes in thermal radiation and mechanical parameters. A relationship between the nonlinear deformation stages and the features of thermomechanical processes is found. The rate of change in rock stress state is shown to affect the information value of variations in the attendant infrared radiation. The experimental results point out the possibility of using the method in monitoring of the real geomechanical objects.

The Catastrophe Model Research of Rock Instability of Tunnel Blot-Grouting Support Structure

The tunnel excavation destroys rock stress state and when concentrated stress exceeds the strength of surrounding rock, the tunnel periphery rocks will be destroyed. And the effective bearing ring will be soon instable and it needs to be supported. Blot-grouting support is an active support method which organically combines shotcreting support and grouting consolidation and its theoretical research achievements are less. This paper, starting from catastrophe theory, established catastrophe instability model of blot-grouting support body and it also obtained the mechanic judgment criterion of blot-grouting support body damage and the regular pattern of the point (N, q)’s motion tract in the controlling space, of which the influence to the rock stability. And the paper also judged the minimum thickness of blot-grouting support body in the point of catastrophe stability model to provide the basis for theoretical calculation and engineering application.

Research on Stress Distribution of Deep Rock by Mechanical Impact Parameters

Domestic and foreign scholars have been studied rock characteristics , but the study results not nearly same with rock nonlinear characteristics. it different rock crushing test conducted many studies ,because it has not the rock broken theoretical basis .This paper try to study the deep rock distribution (under the load before static load) by concentrated load ,it is proposed for deep rock fragmentation theory and methods. In the rock is often under stress , the stress number is measure pressure ,the rock stress state is Related for the elastic potential energy stored and the energy is proportional to the rock depth and volume occurrence. when the stress turned from ,the rock energy will accumulate or release .when the rock energy release ,the rock particles displacement may be elastic displacement or plastic displacement.

Assessment of stress state in rocks by deformation characteristic of borehole zone with hydrofracture

The authors propose the method of stress state assessment in permeable rocks. The method is numerically studied as the relationship between cross-section area of borehole length interval with a hydrofracture and the loading pressure on the borehole walls. The test data processing algorithm and the practical application of the method are considered.

Study on the Influence of Seepage Behavior of Dam Foundation during Wenchuan Earthquake

Earthquake occurred on May 12, 2008 in Wenchuan, Sichuan Province, China, with magnitude of 8.0 and epicenter intensity of VI. Chencun hydropower station in southern Anhui Province has been shocked strongly during Wenchuan Earthquake, which stations 1,500 km away from Wenchuan. Tectonic stress caused by strong earthquakes inevitably led to the changes of stress state, groundwater level and pore pressure in the dam foundation. Seepage water level observation of the dam foundation had been encrypted immediately. According to the experimental data, it was conformed that significant effects were displayed on the dam foundation seepage because of Wenchuan earthquake, shunhe fault near dam sites was the main effect zone of earthquake tectonic stress, the downrange of groundwater depth was self-evident. As the existence of acrylamide curtain, swelling-shrinkage property of the acrylamide gel restricted the change of groundwater level and rock stress state in the dam foundation caused by seismic tectonic stress; the groundwater level behind the acrylamide curtain had a small decline, and recovering quickly.

Study of the borehole hydraulic fracturing and the principle of gas seepage in the coal seam

Coal seam gas has become one of the important factors restricting the safe production of mine in China, so it is urgent to solve the methane problem existing in coal mines. Ground gas drainage method is an easy technology to reduce the gas content in coal seam effectively. However, in China, the coal seam generally possess some characteristics, such as low pressure, low permeability, low saturation, and so forth, which means the borehole hydraulic fracturing must be carried out to improve the permeability of coal seam. The study on the hydraulic fracturing in coal seam is still in an early stage, therefore, the initiation and propagation mechanism of the crack as well as the gas seepage in crack are needed to study deeply. In this paper, firstly, the initiation and propagation mechanism of the crack is theoretically analyzed; then, the principle of gas seepage in cracks and the hydraulic fracturing progress are analyzed synthetically through numerical simulation. The results show that three-dimensional model of fracture propagation for the hydraulic fracturing is established. The stress state of rock has a great effect on the crack propagation. When the two ground stress on horizontal plane is equal, the crack propagates randomly with bifurcation phenomenon; however, when this two stress are different, the direction of the initiation and propagation of the crack is vertical to the minimum main stress. The appropriate pattern shape of borehole is diamond, and the diagonal lines should separately parallel to the maximum principal stress and the minimum principal stress. After fracturing, the accumulative volume of gas production behaves a logarithmic relationship with time, while the volume of gas production represents a negative exponent relationship with time.

Theoretical and numerical study on uniaxial compressive behaviour of marl

Rock matrix failure modes and the consequent material strength are related to the testing conditions, such as the friction value at the rock press contact and the testing velocity, and to the shape and volume of the rock specimen. However, when differences are observed even in specimens having the same rock types in similar boundary conditions, the presence of microscopic cracks is assumed even when they are not directly observable. Porosity is a constant natural presence in rocks with different percentages and shapes whilst cracks can also be induced by rock sampling procedures and by specimen preparation. Defects of both natures (pores and cracks) influence the failure mode and the consequent mechanical features. However, the relation between failure mode and rock strength is not clear yet. This work is aimed to analyze the connection among several aspects influencing rock failure modes by means of laboratory testing in uniaxial condition and tridimensional numerical modeling. The study concerns a French marl chosen for its homogeneity and uniformity when compared to other marls. Specimens with different shapes and volumes were tested with two different laboratory devices equipped with different displacement measuring systems. Numerical modeling reproducing laboratory testing was carried out with the aim of gathering further information concerning the rock stress and strain state during loading. Moreover, the influence of different friction values between the rocks and the press and different rock porosity values have also been considered.

我が国における地下岩盤内の初期地圧状態

我が国における地下岩盤内の初期地圧状態

Distinct analysis of fully grouted bolts around a circular tunnel considering the congruence of displacements between the bar and the rock

This paper presents a new calculation procedure for the analysis and dimensioning of fully grouted radial bolts in tunnels. This procedure is based on the principle of congruency of the displacements, imposing the conditon that the lengthening of the bolt, added to the displacements due to the shear strains in the bolt–rock interface, is equal to the expansion in the radial direction of the reinforced rock annulus. A comparison of the results obtained using this procedure with those obtained using the traditional numerical modelling method, which is more costly in computational terms, has led to satisfactory results. The application of the procedure to a real case has given results that are comparable with the in situ measurements. The proposed instrument is able to analyse the stress and strain state in rock in detail, in the presence of a bolting intervention, and to proceed with its correct dimensioning with the objective of improving the degree of stability of the rock around the tunnel.

Innovative testing technique of rock subjected to coupled static and dynamic loads

A new testing technique, which relates the physical stress state of rock subjected to simultaneous coupled static and dynamic stresses, is presented. The method involves modification of a split Hopkinson pressure bar, such that the test specimen is subjected to coupled axial static pre-stress, axial impact loading, and optional confining pressure. Tests on siltstone specimens with different coupling loads showed that the strength of the specimens under coupling loads was higher than their corresponding individual static or dynamic strengths. In the grade size distribution, the percentage of small size particles of fractured specimen increases with higher coupling loads. The strength of rock under coupling loads decreases rapidly when the axial pre-compression stress is greater than 70% of the static strength of rock (with identical impact loading). However, with constant axial pre-compression stress and increasing impact loading, the strength of siltstone increases initially and reaches a maximum constant value.

The Experimental Study on Fracture Characteristic of Rock

Based on the stress analyses on the surrounding rockmass of underground caverns, the stress states on the surface and inside the surrounding rockmass are simulated respectively using biaxial compression tests and truly triaxial compression tests, and the fracture characteristic of rock and the relation between the angle of rock rupture,θ ,and stress state are studied. According to the testing results, the stress state condition of different type of rock bursts generating in different regions of the surrounding rockmass. The research results show that the rock burst of flake-splitting type takes place around the cavern’s surface under the biaxial compression stress state whereas that of shearing-dislocation type takes place inside the surrounding rockmass under the stress state of truly triaxial compression.

Conceptual and numerical models of ring-fault formation

Most ring faults of collapse calderas are primarily shear fractures the initiation and development of which depends on the state of stress in the host rock. The state of stress in a volcano is controlled by the loading conditions, such as magma-chamber geometry and pressure, but also by the mechanical properties of its rock units and structures (such as existing contacts, faults, and joints). Ring-fault formation is thus essentially a problem in rock physics. Field observations show that some ring faults are dip–slip, whereas others are partly faults (shear fractures) and partly ring dykes (extension fractures). Although slip on existing ring faults is much more common in basaltic edifices (shield volcanoes) than in true composite volcanoes, in both types of volcanoes most caldera unrest periods do not result in ring-fault slip. Here I present new conceptual and numerical models of caldera formation in volcanoes with shallow spherical (circular) or oblate ellipsoidal (sill-like) magma chambers. In the layered models, the host rock above the chamber is composed of 30 comparatively thin layers with stiffnesses (Young's moduli) alternating between 1 GPa and 100 GPa. The chamber itself is located in a single, thick layer. The crustal segment hosting the chamber is either 20 km or 40 km wide but has a constant thickness of 20 km. The loading conditions considered are: (1) a crustal segment subject to 5 MPa tension; (2) crustal segment subject to excess magmatic pressure of 10 MPa at the bottom (doming of the volcanic field containing the chamber); (3) a combination of tension and doming; and (4) chamber subject to underpressure (negative excess pressure) of 5 MPa. The main results are as follows: (1) Excess pressure and underpressure in a chamber normally favour dyke injection rather than ring-fault formation. (2) For doming or tension, a spherical magma chamber favours dyke injection except when the layer hosting the chamber is very soft (10 GPa) or one with recent dyke injections, in which case the surface stress field favours ring-fault formation. (3) For a sill-like chamber in a 20-km wide crustal segment, a ring-fault can be generated by either tension or tension and doming; for a 40-km wide segment, doming alone is sufficient to generate a ring fault. (4) Since individual layers in a volcano may develop different local stresses, stress-field homogenisation through all the layers between the chamber and the surface is a necessary condition for ring-fault formation. (5) Because the mechanical properties of the layers that constitute basaltic edifices are more uniform than those that constitute true composite volcanoes, it follows that stress-field homogenisation, and thus ring-fault formation or slip, is more commonly reached in basaltic edifices than in composite volcanoes. (6) Both for basaltic edifices and composite volcanoes, the stress fields most likely to initiate ring faults are those generated around sill-like chambers subject to tension, doming, or both.

Hydraulic‐fracturing controlled dynamics of microseismic clouds

Several dynamic processes related to propagation of hydraulic fracture modify the stress state in rocks and, therefore, they are relevant for triggering of microseismicity. For instance, these are the creation of a new fracture volume, fracturing fluid loss and its infiltration into reservoir rocks as well as diffusion of the injection pressure into the pore space of surrounding rocks and inside the fracture. Using real data, we show that some of these processes can be seen from features of spatio‐temporal distributions of the induced microseismicity. Especially, the initial stage of fracture volume opening as well as the back front of the induced seismicity starting to propagate after termination of the fluid injection can be well identified and used for reservoir engineering.

Development of Stress Measuring System by Overcoring Method Suitable for Soft Rocks

Most in-situ data on rock stresses are from hard or moderately hard rock. It is necessary to develop a stress measurement method for soft rock, toward obtaining the in-situ stress state in such rock. We developed a stress meter that measures seven components of diametrical deformation and axial deformation in a pilot borehole during overcoring and records the measurements on a small data logger installed within it. From these deformation data, three-dimensional stress states in rock are determined using the observation equation derived from the analytical elastic solution. The stress meter is inserted into a 40-mm pilot borehole that can range in water content from dry to completely wet. The advantages of this stress meter are its smallness, ease of use, reusability, ability to measure at any borehole depth, and efficiency, since very little time is required for insertion and withdrawal and no time is needed to shift from insertion to overcoring. Moreover, elastic properties of the rock can be measured using the core in which the stress meter sits. Although the system is particularly suited to soft rock, it is applicable to any type of rock since the stress meter is highly sensitive.Laboratory experiments simulated the functioning of the stress measuring system by using three welded tuff blocks (40 × 40 × 40 cm) with boreholes 40 mm in diameter at different orientations. The stress meter was inserted into the borehole and two cycles of uniaxial loading and unloading were carried out to simulate the stress relief. At same time, elastic properties of the rock were measured using the above-mentioned method. The calculated stresses were found to correlate closely with the applied stresses in all three cases, indicating that the stress meter functions well.

Enhancing rock stress understanding through numerical analysis

Numerical analysis provides a useful tool to enhance the understanding of rock stress. This paper presents several applications of numerical analysis to evaluate the influence of different factors, such as topology, excavation, loading history and geologic structure, on the state of stress in rock. The discussion focuses on the numerical technique known as the explicit, dynamic solution scheme, and describes how this scheme is well suited to simulate these factors. Recent advances with the explicit solution method are also presented, including the correlation of this method to acoustic and microseismic data to determine stress state information. Future development involves the extension of three-dimensional explicit solution models to simulate large-scale regions of a rock mass. An approach to this development is outlined.

Relationships between gas geochemistry and release rates and the geomechanical state of igneous rock massifs

In contrast to sedimentary sequences, the relationships between the stressed state of igneous rocks and the chemistry and physical properties of gases contained within them are not well known. Here, we attempt to fill this gap by using, as an example, the apatite–nepheline and rare-metal ore deposits hosted within the Khibiny and Lovozero alkaline nepheline–syenite complexes of the Kola Peninsula, NW Russia. These massifs are characterized by unusually high, for igneous rocks, contents of multi-component, essentially hydrogen–hydrocarbon, gases and also by high hardness, elasticity and unevenly distributed, subhorizontal tectonic stresses. Relationships between the chemical and dynamic characteristics of the gases and the geomechanical properties of the host rocks have been examined using field observations and laboratory experiments. Patterns of gas release variations in time and space, gas emissions from rock pillars during artificial loading, variations of gas pressure in sealed shot-holes and changes in liberation rates of gaseous components during experimental rock loading are suggested to result from changes in rock stress and deformation state. Gas compositions in sealed shot-holes in stressed rocks change with time. Partly, this is due to belated release of gases held in fluid inclusions and isolated voids and their subsequent mixing with gases held in interconnected fracture systems as the included gases are preferentially released as fluid inclusion arrays are opened during later stages of stress build-up. Partly, it may also be because released gases may react with new fracture surfaces to generate enhanced levels of reduced H2 gases.