How hydrofractures become arrested

Fluids in the earth's crust are commonly transported by hydrofractures, such as dykes and mineral veins, many of which become arrested at various crustal depths. Hydrofractures are commonly arrested – some showing blunt tips – at contacts between soft (low Young's modulus) and stiff (high Young's modulus) layers. For example, many dyke tips are arrested at contacts between soft pyroclastic rocks and stiff basaltic lava flows, and vein tips at contacts between soft marl and stiff limestone. Theoretical models indicate that overpressured, buoyant hydrofractures in homogeneous, isotropic host rocks should normally reach the surface. In layered host rocks, however, abrupt changes in Young's moduli, horizontal discontinuities, and layers with unusually high fracture-perpendicular stresses encourage hydrofracture arrest. It is proposed that for layer-parallel loading, stiff layers favour hydrofracture arrest during active compression but soft layers during extension. It is concluded that for hydrofracture propagation to occur, the stress field along its potential pathway must be essentially homogenous.     

Stress estimates from the length/width ratios of fractures

The hypothesis is advanced that, provided Young's modulus and Poisson's ratio of the rock are known, the length/width ratios of tension fractures can be used to estimate the tensile stress (assumed constant along the length of each fracture) at the time of fracture formation. The hypothesis is tested on a fissure swarm in a 10,000 year-old basaltic lava in Iceland. The length/width ratios of the fissures give the average tensile stress as of the order of a few MPa.     

等效岩体技术在断续双节理岩石试件破裂机制细观分析中的应用

采用等效岩体技术,将岩体中的岩块和节理分别用颗粒体模型和光滑节理模型描述,从细观角度开展了人工预制含两条断续节理岩石试件力学特性及破裂机制的研究。同时,结合室内试验研究成果,通过计算与试验结果的对比分析,验证了等效岩体技术在断续节理岩体力学特性研究中的适宜性和可靠性。主要研究结果如下：（1）随着断续节理产状的不同,虽可将宏观破裂划分为剪切模式、翼型张拉模式和混合模式等3种类型,但从细观角度看,颗粒间张拉型微破裂均是引起各类宏观破裂模式的主要诱因。（2）在试样达到抗压强度前,破裂声发射事件次数较少,强度均较低,主要孕育于断续节理尖端处,并沿两断续节理尖端的连线在岩桥区域累积贯通。（3）在试样达到抗压强度后,破裂声发射事件次数迅速增加,且破裂强度有所提高。（4）各类试样中,声发射事件累积数和破裂强度之间均近似满足Doseresp生长函数关系。     

Can tensile stress develop in fractured multilayers under compressive strain conditions?

To contribute to the understanding of how opening-mode fractures (joints) form and open or close at depth in layered rocks, we present a 2D numerical study aiming to determine whether tensile stress can develop in pre-fractured elastic multilayers submitted to biaxial compressive strain conditions.First, we investigate the role of the elastic and geometrical properties of the layers on the development of tensile stress in models with five bonded layers and containing one open fracture in the central layer. Our results indicate that, in absence of elastic contrast (in Young's modulus) between the layers, no tensile stress develops in the models. However, when the fractured layer is stiffer than the two adjacent layers directly above and below, a lobe of horizontal tensile stress develops centered on the pre-existing fracture. The creation of this tensile stress is contingent upon the partial closing of the fracture. The levels of tensile stress and the thickness of the lobe of tensile stress increase logarithmically with an increase in the elastic contrast and are systematically larger for a larger Soft/Stiff ratio (ratio of the total thickness of the soft layers with the total thickness of the stiff layers).Second, we investigate the role of fracture interaction in the development of tensile stress in models containing a pair of open fractures. We observe that the levels of tensile stress in the region between the fractures are systematically higher than those observed in identical models containing a single fracture. This increase in tensile stress is very large for small elastic contrasts between the layers but diminishes when the elastic contrast increases. Furthermore, the spacing between the pre-existing fractures plays an important role in the stress distribution in the region between them. When the fracture spacing is equal to or lower than 1.15 times the height of the fractured layer for the experimental conditions chosen, the lobes of tensile stress centered on the fractures coalesce. This results in the formation of vast areas of tensile stress in models under remote compressive loading conditions. Such tensile areas are likely to allow the initiation and propagation of subsequent opening-mode fractures.The results obtained provide new insights into the formation of joints in layered rocks in compressive environments, with important consequences on fluid flow.     

Coalescence of offset rock joints under biaxial loading

Crack coalescence in rock masses was studied by performing a series of biaxial compresion tests on specimens made of rock-like material. Specimens of size 63.5 × 27.9 × 20.3 cm, made of 72% silica sand, 16% cement (Type I) and 12% water by weight were tested. The joint inclination angle was maintained at 45°, while the offset angle i.e. angle between the plane of the joint and the line that connects the two inner tips of the joints, was changed from 0° to 90° with an increment of 15°. Three levels of lateral stress were used; 0.35 MPa, 0.7 MPa and 1.5 MPa on each sample. HP data acquisition system was used to record the data for each sample. In each sample, four LVDTs were fixed to measure the axial and lateral displacement along the sample. The failure mechanisms were monitored by eye inspection and a magnifier to detect crack initiation and propagation. For each test, the failure surfaces were investigated to determine the characteristics of each surface. Wing cracks initiated at the tip of the joint for the low confining stress applied, while at higher confining stresses wing cracks also initiated at the middle of the joint. Secondary cracks initiated at the tip of the joint due to shear stress. Three modes of failure took place due to coalescence of the secondary and wing cracks. The bridge inclination was the main variable that controlled the mode of failure. For bridge inclination of 0°, the coalescence occured due to shear failure and for bridge inclination of 90° the coalescence occurred due to tensile failure while for the other bridge inclinations coalescence occured due to mixed tensile and shear failure.     

Development of a full 3D numerical model to investigate the hydraulic fracture propagation under the impact of orthogonal natural fractures

Although hydraulic fracturing has been massively studied and applied as a key technique to enhance the gas production from tight formations, some problems and uncertainties exist to accurately predict and analyze the fracture behavior in complex reservoirs, especially in the naturally fractured reservoirs like shale reservoirs. This paper presents a full 3D numerical model (FLAC3D) to study hydraulic fracturing behavior under the impact of preexisting orthogonal natural fractures. In this numerical model, the hydraulic fracture propagation direction is assumed perpendicular to the minimum principal stress and activated only by tensile failure, whereas the preexisting natural fractures can be activated by tensile or shear failure or a combination of them, and only tensile failure can open the natural fracture as well. The newly developed model was used to study the impact of preexisting orthogonal natural fractures on hydraulic fracturing behavior, based on a multistage hydraulic fracturing operation in a naturally fractured reservoir from the Barnett Shale formation, northwest of Texas in USA. In this multistage operation, two more representative stages, i.e., stage 1 with a relatively large horizontal stress anisotropy of 3.3 MPa and stage 4 with a comparatively small one of 1.3 MPa, were selected to conduct the simulation. Based on the numerical results, one can observe that the interaction between hydraulic and natural fracture is driven mainly by induced stress around fracture tip. Besides, the horizontal stress anisotropy plays a key role in opening the natural fracture. Thus, no significant opened fracture is activated on natural fracture in stage 1, while in stage 4 an opened fracture invades to about 90 m into the first natural fracture. Conversely, the hydraulic fracture length in stage 1 is much longer than in stage 4, as some fluid volume is stored in the opened natural fracture in stage 4. In this work, the shear failure on natural fractures is treated as the main factor for inducing the seismic events. And the simulated seismic events, i.e., shear failure on natural fractures, are very comparable with the measured seismic events.

     

Fracture termination and step-over at bedding interfaces due to frictional slip and interface opening

Three types of fracture intersection with bedding contacts have been investigated within numerical experiments: fracture transection through bed contacts, termination (abutment) at contacts and step-over of fractures at bedding contacts. To evaluate the mechanisms responsible for different fracture intersections with bed contacts, the numerical experiments explored deformation associated with end-member conditions of sliding-only interfaces and opening-only interfaces. A third suite of models explored the combined influence of both sliding and opening, as a fracture approached the interface. In contrast to our initial supposition that interface sliding promotes fracture termination, the sliding-only interfaces encouraged propagation of fractures straight through the modeled interface. In contrast, the opening-only interfaces yielded either fracture termination or initiation of a new fracture near the ends of the open interface segment (several centimeters from parent fracture in these models). These results suggest that local interface opening near the tip of approaching fractures, rather than sliding, is responsible for fracture termination and step-over at bedding contacts. Combined sliding and opening yielded fracture termination in models with weak interfaces (μ=0; c=0 MPa; T=0 MPa) and either fracture step-over or termination at moderate-strength interfaces (μ=0.65; c=3.25 MPa; T=5 MPa). Fracture termination occurs at moderate-strength interfaces when the stresses along the interface are not great enough to initiate a new step-over fracture. Fracture termination is more likely under conditions of shallower burial depth, lower layer-parallel effective tension and fluid-driven fracture propagation rather than remote layer-parallel tension. Furthermore, thicker beds and greater layer-parallel effective tension may produce greater distances of fracture step-over than thinner beds and more compressive layers. These results may assist in the prediction of subsurface fracture networks and associated fluid flow paths.     

Limits on strength and deformation properties of jointed basaltic rock masses

Summary A study of strength and deformation measurements for basaltic rocks, along with consideration of the influence of fracturing using a rock mass classification system, documents the range of brittle response for basaltic rock masses. Although basalts vary widely in composition and other physical factors, many of the properties of a basaltic rock mass appear to vary within a factor of about 10. Typical values of strength parameters for intact basalt at ambient temperature (20°C) and negligible confining pressure are Young's modulus, 78±19 GPa; Poisson's ratio, 0.25±0.05; tensile strength, –14.5±3.3 MPa; unconfined compressive strength, 266±98 MPa; and conhesion, 66 MPa. Corresponding values for a basaltic rock mass that incorporate the weakening effects of scale are deformation modulus, 10–40 GPa; Poisson's ratio, 0.3; tensile strength, –0.1 to –2.5 MPa; uniaxial compressive strength, 10–90 MPa; and cohesion, 0.6–6 MPa. A measured deformation modulus for ambient pressure in the vertical direction, 20 GPa, is 1.5–3 times larger than that in the horizontal directions, 13.5 and 6.5 GPa, reflecting strength anisotropy due to column or block geometry for one particular basalt. Values of tensile and cohesive strength for the basaltic rock mass are generally one to two orders of magnitude lower than corresponding values for intact basalt. The shear strength of joints appears to vary considerably from flow to flow.     

Effects of mechanical layering on hydraulic fracturing in shale gas reservoirs based on numerical models

Generally, induced hydraulic fractures are generated by fluid overpressure and are used to increase reservoir permeability through forming interconnected fracture systems. However, in heterogeneous and anisotropic rocks, many hydraulic fractures may become arrested or offset at layer contacts under certain conditions and do not form vertically connected fracture networks. Mechanical layering is an important factor causing anisotropy in sedimentary layers. Hence, in this study, with a shale gas reservoir case study in the Longmaxi Formation in the southeastern Chongqing region, Sichuan Basin, we present results from several numerical models to gain quantitative insights into the effects of mechanical layering on hydraulic fracturing. Results showed that the fractured area caused by hydraulic fracturing indicated a linear relationship with the neighboring layer’s Young’s modulus. An increase of the neighboring layer’s Young’s modulus resulted in better hydraulic fracturing effects. In addition, the contact between two neighboring layers is regarded as a zone with thickness and mechanical properties, which also influences the effects of hydraulic fracturing in reservoirs. The initial hydraulic fracture was unable to propagate into neighboring layers under a relatively low contact’s Young’s modulus. When associated local tensile stresses exceeded the rock strength, hydraulic fractures propagated into neighboring layers. Moreover, with the contact’s Young’s modulus becoming higher, the fractured area increased rapidly first, then slowly and finally became stable.     

Predicting mechanical properties and ultimate shear strength of gypsum,limestone and sandstone rocks using Vipulanandan models

ABSTRACT

In this study, over 1000 data from the literature was used to characterize and compare the density, strengths, modulus, fracture toughness, porosity and the ultimate shear strengths of the gypsum, limestone and sandstone rocks. The compressive modulus and Mode-1 fracture toughness of the gypsum rock, limestone rock and sandstone rocks varied from 0.7 GPa to 70 GPa, and from 0.03 MPa.m^0.5 to 2.6 MPa.m^0.5  respectively. Vipulanandan correlation model was effective in relating the modulus of elasticity, fracture toughness with the relevant strengths of the rocks. A new nonlinear Vipulanandan failure criterion was developed to quantify the tensile strength, pure shear (cohesion) strength and to predict the maximum shear strength limit with applied normal stress on the gypsum, limestone and sandstone rocks. The Vipulanandan failure model predicts the maximum shear strength limit was, as the Mohr-Coulomb failure model does not have a limit on the maximum shear strength. With the Vipulanandan failure model based on the available data, the maximum shear strengths predicted for the gypsum, limestone and sandstone rocks were 64 MPa, 114 MPa and 410 MPa respectively.     

High temperature fracturing and ductile deformation during cooling of a pluton: The Lake Edison granodiorite (Sierra Nevada batholith,California)

In the Bear Creek area of the Sierra Nevada batholith, California, the high temperature postmagmatic deformation structures of the Lake Edison granodiorite include steeply-dipping orthogneiss foliations, joints, and ductile shear zones that nucleated on joints and leucocratic dykes. Exploitation of segmented joints resulted in sharply bounded, thin shear zones and in large slip gradients near the shear zone tips causing the deformation of the host rock at contractional domains. The orthogneiss foliation intensifies towards the contact with the younger Mono Creek granite and locally defines the dextral Rosy Finch Shear Zone (RFSZ), a major kilometre-wide zone crosscutting the pluton contacts. Joints predominantly strike at N70–90°E over most of the Lake Edison pluton and are exploited as sinistral shear zones, both within and outside the RFSZ. In a narrow (∼250 m thick) zone at the contact with the younger Mono Creek granite, within the RFSZ, the Lake Edison granodiorite includes different sets of dextral and sinistral shear zones/joints (the latter corresponding to the set that dominates over the rest of the Lake Edison pluton). These shear zones/joints potentially fit with a composite Y–R–R′ shear fracture pattern associated with the RFSZ, or with a pattern consisting of Y–R-shear fractures and rotated T′ mode I extensional fractures. The mineral assemblage of shear zones, and the microstructure and texture of quartz mylonites indicate that ductile deformation occurred above 500 °C. Joints and ductile shearing alternated and developed coevally. The existing kinematic models do not fully capture the structural complexity of the area or the spatial distribution of the deformation and magmatic structures. Future models should account more completely for the character of ductile and brittle deformation as these plutons were emplaced and cooled.     

Numerical models of hydraulic fracturing and the interpretation of syntectonic veins

The hydraulic fracture is modelled as an ellipse in an infinite elastic medium with an internal fluid pressure and loaded under biaxial stresses at infinity. The available stress function for this model has been evaluated numerically, and the magnitudes of the stresses generated around the crack calculated for a variety of loading conditions and crack orientations. Fracture initiation is predicted from the Griffith maximum tensile stress criterion. The location of the maximum tensile stress around the crack is recorded and it is found that for many conditions of applied stresses and crack fluid pressure, the hydraulic shear fracture has a symmetrically developed maximum tensile stress and fracture initiation will occur by growth along the direction of the crack. It is also predicted that fracture initiation will occur when the ratio of fluid pressure to applied least principal stress is considerably less than one. The elastic strain energy fields around elliptical hydraulic flaws have been calculated, and in particular, the change in strain energy upon introduction of a small flaw, and the change in strain energy upon growth of this flaw, have been investigated. The results allow an evaluation of the second part of the Griffith criterion-that fracture growth is accompanied by a decrease in strain energy-for hydraulic fractures. Changes in strain energy with small increases in fluid pressure provide a physical basis for dilatancy hardening and fracture instability. Quasi-static growth from a flaw is modelled by calculating changes in strain energy for unit increases in half length. The distinction between fractures which show an increasing and a decreasing rate of change in strain energy with increasing length, and between fractures which may only extend spontaneously for short distances and those which may show extensive spontaneous growth on the basis of the rate of change of strain energy with length, is made. A gradual drop in crack fluid pressure once the threshold for fracture initiation has been passed may promote the extent to which spontaneous crack growth occurs.The formation of syntectonic veins, particularly in rocks being deformed under low grade metamorphic conditions, is often the most abundant evidence of natural hydraulic fracturing in rocks. Commonly observed geometric features of syntectonic veins-length, simple tapering, symmetric and asymmetric forking, branching, irregular zig-zag traces, en échelon patterns—are discussed primarily with reference to the strain energy model for growth established, and the geometric variation is interpreted in terms of variation in applied stress and fluid pressure conditions and the rate of change of stored strain energy with crack growth. In particular, terminal branching arises when the minimum stress changes from a symmetric to an asymmetric location at the tip of a growing shear fracture, and terminal forking results when there is an increase in the energy release rate during crack growth, and may be symmetric or asymmetric depending on the location of the minimum stress at the crack tip at the time of forking.     

Role of heterogeneities in jointing (fracturing) of geological media: Numerical analysis of fracture mechanisms

Fracture process is investigated using finite-difference simulations with a new constitutive model. It is shown that both geometry and fracture mechanism itself depend on the preexisting heterogeneities that are stress concentrators. In the brittle regime (low pressure, P), Mode-I fractures propagate normal to the least stress σ₃ from the imposed weak zones. At high P, shear deformation bands are formed oblique to σ₃. At intermediate values of P, the fracture process involves both shear banding and tensile cracking and results in the initiation and propagation of pure dilation bands. The propagating band tip undulates, reacting on the failure mechanism changes, but its global orientation is normal to σ₃. The σ₃-normal fractures are joints. There are thus two types of joints resulting from Mode-I cracking and dilation banding, respectively. The obtained numerical results are in good agreement with and explain the results from previous similar experimental study.     

Physical explanation for the displacement-length relationship of faults using a post-yield fracture mechanics model

A plane strain model for a fault is presented that takes into account the inelastic deformation involved in fault growth. The model requires that the stresses at the tip of the fault never exceed the shear strength of the surrounding rock. This is achieved by taking into account a zone, around the perimeter of the fault surface, where the fault is not well developed, and in which sliding involves frictional work in excess of that required for sliding on the fully developed fault. The displacement profiles predicted by the fault model taper out gradually towards the tip of the fault and compare well with observed displacement profiles on faults. Using this model it is found that both (1) the shape of the displacement profile, and (2) the ratio of maximum displacement to fault length are a function of the shear strength of the rock in which the fault forms. For the case of a fault loaded by a constant remote stress, the displacement is linearly related to the length of the fault and the constant of proportionality depends on the shear strength of the surrounding rock normalized by its shear modulus. Using data from faults in different tectonic regions and rock types, the in situ strength of intact rock surrounding a fault is calculated to be on the order of 100 MPa (or a few kilobars). These estimates exceed, by perhaps a factor of 10, the strength of a well developed fault and thus provide an upper bound for the shear strength of the crust. It is also shown that the work required to propagate a fault scales with fault length. This result can explain the observation that the fracture energy calculated for earthquake ruptures and natural faults are several orders of magnitude greater than that for fractures in laboratory experiments.     

非贯通节理岩体直剪试验研究进展

基于典型的直剪试验,国内外学者提出了非贯通节理岩体贯通破坏机理,并建立了相应的强度准则,如Jennings方法,即加权平均强度理论和强度准则、Lajtai岩桥破坏理论和强度准则、断裂力学的II型破坏理论和强度准则,拉剪复合破坏和强度准则。然而,非贯通节理岩体破坏机理目前还没有完全弄清楚,已建立的强度准则所包含的重要参数还需深入研究,如：如节理面的传压系数、传剪系数、弱化了的岩桥内摩擦力和内摩擦角等;非贯通节理岩体节理闭合和剪切的本构关系有待建立;不共面非贯通节理岩体全过程最大抗剪强度需进一步研究。伺服直剪试验机、静态应变测试仪、声发射仪、X射线测量等无损检测技术能够为进一步研究非贯通节理岩体的破坏机理,提出新的理论和建立新的强度准则提供强有力的技术支持。     

Transitional–tensile fracture propagation: a status report

One model for the development of hybrid shear fractures is transitional–tensile fracture propagation, a process described as the in-plane propagation of a crack subject to a shear traction while held open by a tensile normal stress. Presumably, such propagation leads to a brittle structure that is the hybrid of a joint and a shear fracture. Crack–seal veins with oblique fibers are possible candidates. While these veins clearly show shear offset, this is not conclusive evidence that a shear traction was present at the time of initial crack propagation. Many recent structural geology textbooks use a parabolic Coulomb–Mohr failure envelope to explain the mechanics of transitional–tensile fracturing. However, the laboratory experiments cited as demonstrating transitional–tensile behavior fail to produce the fracture orientation predicted by a parabolic failure envelope. Additional attempts at verification include field examples of conjugate joint sets with small acute angles, but these conjugate joints form neither simultaneously nor in the stress field required by the transitional–tensile model. Finally, linear elastic fracture mechanics provides strong theoretical grounds for rejecting the notion that individual cracks propagate in their own plane when subject to a shear traction. These observations suggest that transitional–tensile fracture propagation is unlikely to occur in homogeneous, isotropic rock, and that it is not explained by a parabolic Coulomb–Mohr failure envelope as several recent structural geology textbooks have suggested.     

天然裂缝影响下的花岗岩水力裂缝扩展数值模拟

水力压裂技术是成功实现干热岩资源开发利用的重要手段之一,数值模拟技术能够精准预测水力裂缝扩展。针对典型花岗岩,借助黏性单元法,分别模拟了致密花岗岩和天然裂缝存在情况下的水力裂缝扩展特征,得出以下结论:致密花岗岩的水力裂缝形态单一,天然裂缝的存在增加了压裂后裂缝的复杂性;致密花岗岩水力裂缝拓展主要分为憋压和拓展两个交替往复的阶段,当存在天然裂隙时,水力压裂过程会变得复杂;天然裂缝存在时,水力裂缝的缝长和缝宽分别为致密花岗岩的5.7倍和1.7倍;缝网的形成需要借助复杂的压裂工艺实现。研究结果可以为增强型地热系统(EGS)储层水力刺激工作提供理论支持。     

Shear behaviour of fractured rock as a function of size and shear displacement

This paper presents laboratory results regarding the shear behaviour of an artificial tensile fracture generated in granite. We used a direct shear rig to test fractures of different sizes (from 100 mm to 200 mm) under various shear displacements up to 20 mm and cyclic shear stresses with constant normal stress of 10 MPa. To determine the evolution of surface damage and aperture during shear, cyclic loading was performed at designated shear displacements. These changes in the surfaces topography were measured with a laser profilometer ‘non-contact surface profile measurement system’. In addition, changes were also measured directly by using pressure-sensitive film.

The results showed that the standard deviation (SD) of the initial aperture of the sheared fracture significantly increases with both shear displacement and size, which result in an increase in the non-linearity of the closure curve (since the matedness of the fracture surfaces decreases with shear displacement). Therefore, we concluded that shear dilation is not only governed by the surfaces sliding over each other, but is also strongly influenced by the non-linearity of closure with shear displacement. Furthermore, while the shear stiffness of the fracture during the initial stage decreases with fracture size, it increases with fracture size in the residual stage. This can be attributed to the fact that only small asperities with short wavelengths were mainly damaged by shearing. Moreover the result showed that the damaged zones enlarge and localise with shear displacement, and eventually tend to form perpendicular to the shear displacement.     

Analytical solution of the problem for a set of shear fractures with Coulomb friction

A simplified solution of a two-dimensional problem on a set of interaction shear fractures with Coulomb friction along their wings is proposed. In the classical statement of this problem, the equality between shear stresses and friction stresses must necessarily hold in a new equilibrium state at each point along the fracture plane. The solution of the problem is reduced to the solution of a set of singular integral equations with respect to unknown functions of a shear jump on fractures. In reality, our knowledge of fracture conditions is rather approximate. In addition, in the problems of seismology and tectonophysics it is sufficient to approximately estimate dynamic (taking into account the inertia forces) and static perturbations from a fracture in the form of the first terms of a true solution series. With this aim in view, point models of an earthquake source or continual representation of discontinuous deformations are used. Within the framework of the requirements of such approaches, it is assumed that the condition of equality between the sum of shear stresses and friction stresses on the shear fractures in a new equilibrium state is met. In addition, the complex potential function is calculated for each fracture based on the function of the jump of its wings obtained in the problem for a solitary fracture. Such statement of the problem of a set of neighboring and even intersecting fractures makes it possible to reduce its solution to a set of linear algebraic equations with respect to shear stresses relieved at each fracture and the average along its length, they being the unknown values.     

伊宁吐拉苏火山盆地金矿成矿构造系统与远景评估

吐拉苏火山盆地金矿成矿构造系统由2种类型的成矿构造组成，一种是火山机构中的高角度塌陷式断裂；另一种是爆发．沉积相中的低角度水压式断裂．阿希金矿受控于弧形塌陷式断裂，其北东段坍塌强度大于南东段，最大张裂空间控制的矿体群向NE侧伏．阿希火山机构东侧的阿恰勒河组下可能隐伏着与西侧对应的高角度弧形塌陷式成矿断裂．爆发．沉积相中硅化岩型金矿受控于水压式断裂，不透水凝灰岩层圈闭富水粗火山碎屑岩层，组成压力仓构造并发生水力压裂作用．由水力压裂作用形成的层控水压式成矿断裂出现的几率，远大于后期由非成矿断裂切割抬升它们出现的几率．构造解析表明吐拉苏火山盆地2类成矿构造控制的金矿具有巨大的地质找矿潜力．