Stress tensor determination by modified hydraulic tests on pre-existing fractures:Method and stress constraints

The hydraulic testing of pre-existing fractures(HTPF)is one of the most promising in situ stress measurement methods,particularly for three-dimensional stress tensor determination.However,the stress tensor determination based on the HTPF method requires at least six tests or a minimum of 14-15 tests(under different conditions)for reliable results.In this study,we modified the HTPF method by considering the shear stress on each pre-existing fracture,which increased the number of equations for the stress tensor determination and decreased the number of tests required.Different shear stresses were attributed to different fractures by random sampling;therefore,the stress tensors were obtained by searching for the optimal solution using the least squares criterion based on the Monte Carlo method.Thereafter,we constrained the stress tensor based on the tensile strength criterion,compressive strength criterion,and vertical stress constraints.The inverted stress tensors were presented and analyzed based on the tensorial nature of the stress using the Euclidean mean stress tensor.Two stress-measurement campaigns in Weifang(Shandong Province,China)and Mercantour road tunnel(France)were implemented to highlight the validity and efficiency of the modified HTPF(M-HTPF)method.The results showed that the M-HTPF method can be applied for stress tensor inversion using only three to four tests on pre-existing fractures,neglecting the stress gradient.The inversion results were confined to relatively small distribution dispersions and were significantly reliable and stable due to the shear stresses on the fractures and the stress constraints employed.The M-HTPF method is highly feasible and efficient for complete stress tensor determination in a single borehole.

Using fracture-based continuum modeling of coupled geomechanical-hydrological processes for numerical simulation of hydraulic fracturing

This paper describes numerical simulation of hydraulic fracturing using fracture-based continuum modeling(FBCM)of coupled geomechanical-hydrological processes to evaluate a technique for high-density fracturing and fracture caging.The simulations are innovative because of modeling discrete fractures explicitly in continuum analysis.A key advantage of FBCM is that fracture initiation and propagation are modeled explicitly without changing the domain grid(i.e.no re-meshing).Further,multiple realizations of a preexisting fracture distribution can be analyzed using the same domain grid.The simulated hydraulic fracturing technique consists of pressurizing multiple wells simultaneously:initially without permeating fluids into the rock,to seed fractures uniformly and at high density in the wall rock of the wells;followed by fluid injection to propagate the seeded fracture density hydraulically.FBCM combines the ease of continuum modeling with the potential accuracy of modeling discrete fractures and fracturing explicitly.Fractures are modeled as piecewise planar based on intersections with domain elements;fracture geometry stored as continuum properties is used to calculate parameters needed to model individual fractures;and rock behavior is modeled through tensorial aggregation of the behavior of discrete fractures and unfractured rock.Simulations are presented for previously unfractured rock and for rock with preexisting fractures of horizontal,shallow-dipping,steeply dipping,or vertical orientation.Simulations of a single-well model are used to determine the pattern and spacing for a multiple-well design.The results illustrate high-density fracturing and fracture caging through simultaneous fluid injection in multiple wells:for previously unfractured rock or rock with preexisting shallow-dipping or horizontal fractures,and in situ vertical compressive stress greater than horizontal.If preexisting fractures are steeply dipping or vertical,and considering the same in situ stress condition,well pressurization without fluid permeation appears to be the only practical way to induce new fractures and contain fracturing within the target domain.

Hydraulic Fracture Parameter Inversion Method for Shale Gas Wells Based on Transient Pressure-Drop Analysis during Hydraulic Fracturing Shut-in Period

Horizontal well drilling and multi-stage hydraulic fracturing are key technologies for the development of shale gas reservoirs.Instantaneous acquisition of hydraulic fracture parameters is crucial for evaluating fracturing effectiveness,optimizing processes,and predicting gas productivity.This paper establishes a transient flow model for shale gas wells based on the boundary element method,achieving the characterization of stimulated reservoir volume for a single stage.By integrating pressure monitoring data following the pumping shut-in period of hydraulic fracturing for well testing interpretation,a workflow for inverting fracture parameters of shale gas wells is established.This new method eliminates the need for prolonged production testing and can interpret parameters of individual hydraulic fracture segments,offering significant advantages over the conventional pressure transient analysismethod.The practical application of thismethodology was conducted on 10 shale gaswellswithin the Changning shale gas block of Sichuan,China.The results show a high correlation between the interpreted single-stage total length and surface area of hydraulic fractures and the outcomes of gas production profile tests.Additionally,significant correlations are observed between these parameters and cluster number,horizontal stress difference,and natural fracture density.This demonstrates the effectiveness of the proposed fracture parameter inversion method and the feasibility of field application.The findings of this study aim to provide solutions and references for the inversion of fracture parameters in shale gas wells.

Acoustic emission characterization of microcracking in laboratory-scale hydraulic fracturing tests

Understanding microcracking near coalesced fracture generation is critically important for hydrocarbon and geothermal reservoir characterization as well as damage evaluation in civil engineering structures. Dense and sometimes random microcracking near coalesced fracture formation alters the mechanical properties of the nearby virgin material. Individual microcrack characterization is also significant in quantifying the material changes near the fracture faces （i.e. damage）. Acoustic emission （AE） monitoring and analysis provide unique information regarding the microcracking process temporally, and infor- mation concerning the source characterization of individual microcracks can be extracted. In this context, laboratory hydraulic fracture tests were carried out while monitoring the AEs from several piezoelectric transducers. In-depth post-processing of the AE event data was performed for the purpose of under- standing the individual source mechanisms. Several source characterization techniques including moment tensor inversion, event parametric analysis, and volumetric deformation analysis were adopted. Post-test fracture characterization through coring, slicing and micro-computed tomographic imaging was performed to determine the coalesced fracture location and structure. Distinct differences in fracture characteristics were found spatially in relation to the openhole injection interval. Individual microcrack AE analysis showed substantial energy reduction emanating spatially from the injection interval. It was quantitatively observed that the recorded AE signals provided sufficient information to generalize the damage radiating spatially away from the injection wellbore.

A Reinterpretation of Historic Aquifer Tests of Two Hydraulically Fractured Wells by Application of Inverse Analysis, Derivative Analysis, and Diagnostic Plots

Aquifer test methods have greatly improved in recent years with the advent of inverse analysis, derivative analysis, and diagnostic plots. Updated analyses of past aquifer tests allow for improved interpretations of the data to enhance the knowledge and the predictive capabilities of the flow system. This work thoroughly reanalyzes a series of pre- and post-hydraulic fracturing, single-well aquifer tests conducted in two crystalline rock wells in New Hampshire as part of an early 1970’s study. Previous analyses of the data had relied on older manual type-curve methods for predicting the possible effects of hydraulic fracturing. This work applies inverse analysis, derivative analysis, and diagnostic plots to reanalyze the 1970’s aquifer test data. Our results demonstrate that the aquifer tests were affected by changes in flow regimes, dewatering of the aquifer and discrete fractures, and changes due to well development. Increases in transmissivities are related to well development prior to hydraulic fracturing, propagation of a single, vertical fracture hydraulically connecting the two wells after stimulation and expansion of troughs of depression. After hydraulic fracturing, the estimated total yield of the individual wells increased by 2.5 times due to the hydraulic fracturing. However, the wells may be receiving water from the same source, and well interference may affect any significant increase in their combined yield. Our analyses demonstrate the value in applying inverse analysis, derivative analysis, and diagnostic plots over the conventional method of manual type-curve analysis. In addition, our improvement in the aquifer test interpretation of the 1970’s test data has implications for more reliable estimates of sustained well yields.

A method to experimentally investigate injection-induced activation of fractures

Natural fractures are generally well developed in most hydrocarbon and geothermal reservoirs,which can produce complex fracture networks due to the activation of fractures during hydraulic stimulation.The present paper is devoted to developing a method to investigate the activation characteristics of fracture under injection-shearing coupled condition at laboratory scale.The fluid is injected into the single-fractured granite until the fracture is activated based on the triaxial direct shear tests.The results show that injection process can significantly influence the shear stress distribution field,resulting in release of shear stress and relative slip between the opposite sides of the fractured surface.The injectioninduced activation of fracture is strongly dependent on the stress states.When the normal stress increases,the injection-induced activation pressure increases,and the comparatively high normal stress can restrain the fracture activation.The fracture deformation mechanisms during fluid injection are also discussed preliminarily with the experimental data.The sensitivity of shear stress to fluid injection increases with increase of shear stress level,while it decreases under high normal stress.The results can facilitate our understanding of the natural fracture activation behavior during fluid pressure stimulation.

Effect of height-diameter ratio on the mechanical characteristics of shale with different bedding orientations

Geological exploration cores obtained from shale gas wells several kilometers deep often show different height-diameter ratios(H/D)because of complex geological conditions(core disking or developed fractures),which makes further standard specimen preparation for mechanical evaluation of reservoirs difficult.In multi-cluster hydraulic fracturing,shale reservoirs between planes of hydraulic fractures with different lengths could be simplified to have different H/D ratios.Discovering the effect of H/D on the mechanical characteristics of shale specimens with different bedding orientations will support mechanical evaluation tests of reservoirs based on disked geological cores and help to optimize multicluster fracturing programs.In this study,we performed uniaxial compression tests and acoustic emission(AE)monitoring on cylindrical Longmaxi shale specimens under five bedding orientations and four H/D ratios.The experimental results showed that both the H/D-dependent mechanical properties and AE parameters demonstrated significant anisotropy.Increasing H/D did not change the uniaxial compressive strength(UCS)evolution versus bedding orientation,demonstrating a V-shaped relationship,but enhanced the curve shape.The stress level of crack damage for the specimens significantly increased with increasing H/D,excluding the specimens with a bedding orientation of 0°.With increasing H/D,the cumulative AE counts of the specimens with each bedding orientation tended to exhibit a stepped jump against the loading time.The proportion of low-average-frequency AE signals(below 100 kHz)in specimens with bedding orientations of 45°and 60°increased to over 70%by increasing H/D,but it only increased to 40%in specimens with bedding orientations of 0°,30°,and 90°.Finally,an empirical model that can reveal the effect of H/D on anisotropic UCS of shale reservoir was proposed,the anisotropic proportion of tensile and shear failure cracks in specimens under four H/D ratios was classified based on the AE data,and the effect of H/D on the anisotropic crack growth of specimens was discussed.

引入围岩结构观测系统在地应力测试中的应用

为减小水压致裂法测量地应力时的误差,提高地应力测量成功率与测试结果精度,引入围岩结构观测系统,以某矿8510回风巷为研究背景,开展地应力测试对照试验。试验结果表明:在未引入围岩结果测试系统时,8510回风巷最大水平主应力为8.14 MPa,垂直主应力为11.06 MPa,垂直构造应力占优势,测压比的范围在0.40~0.74之间;引入围岩结构测试系统后,8103回风巷最大水平主应力为14.95 MPa,垂直主应力为11.04 MPa,水平构造应力占优势,测压比的范围在0.69~1.35之间,与区域已测得地应力场较吻合。引入围岩结构测试系统的水压致裂法测量地应力方便、快捷,且所测结果更加真实可靠。

Mutual interference of layer plane and natural fracture in the failure behavior of shale and the mechanism investigation

Shale contains a certain amount of natural fractures,which affects the mechanical properties of shale.In this paper,a bonded-particle model in particle flow code(PFC)is established to simulate the failure process of layered shale under Brazilian tests,under the complex relationship between layer plane and natural fracture.First,a shale model without natural fractures is verified against the experimental results.Then,a natural fracture is embedded in the shale model,where the outcomes indicate that the layer plane angle(marked asα)and the angle(marked asβ)of embedded fracture prominently interfere the failure strength anisotropy and fracture pattern.Finally,sensitivity evaluations suggest that variable tensile/cohesion strength has a changeable influence on failure mechanism of shale,even for sameαor/andβ.To serve this work,the stimulated fractures are categorized into two patterns based on whether they relate to natural fracture or not.Meanwhile,four damage modes and the number of microcracks during the loading process are recognized quantitatively to study the mechanism of shale failure behavior.Considering the failure mechanism determines the outcome of hydraulic fracturing in shale,this work is supposed to provide a significant implication in theory for the engineering operation.

Cause analysis and solutions of water blocking damage in cracked/non-cracked tight sandstone gas reservoirs

After hydraulic fracturing treatment,a reduction in permeability caused by the invasion of fracturing fluids is an inevitable problem,which is called water blocking damage.Therefore,it is important to mitigate and eliminate water blocking damage to improve the flow capacities of formation fluids and flowback rates of the fracturing fluid.However,the steady-state core flow method cannot quickly and accurately evaluate the effects of chemical agents in enhancing the fluid flow capacities in tight reservoirs.This paper introduces a time-saving and accurate method,pressure transmission test(PTT),which can quickly and quantitatively evaluate the liquid flow capacities and gas-drive flowback rates of a new nanoemulsion.Furthermore,scanning electron microscopy(SEM)was used to analyze the damage mechanism of different fluids and the adsorption of chemical agents on the rock surface.Parallel core flow experiments were used to evaluate the effects of the nanoemulsion on enhancing flowback rates in heterogeneous tight reservoirs.Experimental results show that the water blocking damage mechanisms differ in matrices and fractures.The main channels for gas channeling are fractures in cracked cores and pores in non-cracked cores.Cracked cores suffer less damage from water blocking than non-cracked cores,but have a lower potential to reduce water saturation.The PTT and SEM results show that the permeability reduction in tight sandstones caused by invasion of external fluids can be list as guar gum fracturing fluid>slickwater>brine.Parallel core flow experiments show that for low-permeability heterogenous s andstone reservoirs with a certain permeability ratio,the nanoemulsion can not only reduce reverse gas channeling degree,but also increase the flowback rate of the fracturing fluid.The nanoemulsion system provides a new solution to mitigate and eliminate water blocking damage caused by fracturing fluids in tight sandstone gas reservoirs.

Application of gas wettability alteration to improve methane drainage performance:A case study

Hydraulic fracturing technique is widely used for methane drainage and has achieved good effects in numerous coal mines,but negative effects may occur as the fracturing fluids are absorbed into the coal seam.Gas wettability alteration(GWA)technology can be used as it can enhance the gas and water mobility during dewatering process as a result of capillary pressure change.However,there have been few reported field tests in coal mines using GWA technology.This paper describes a pilot-scale field test in Xinjing coal mine,Yangquan,China.The fluorocarbon surfactants perfluorooctyl methacrylate monomer-containing polymethacrylate(PMP)was used to alter the wettability of coal seam to strong gas-wetness during the hydraulic fracturing process.The study focuses on the comparison of two boreholes(Boreholes#9 and#10)and one other borehole(Borehole#8)with and without using GWA approach.A well-defined monitoring program was established by measuring the dewatering volume of the fracturing fluid and the drainage volume of methane as well as the concentration.The field test results showed that the average methane drainage rates of Boreholes#9(39.28 m^(3)/d)and#10(51.04 m^(3)/d)with GWA treatment exceeded that of Borehole#8(21.09 m^(3)/d)without GWA treatment,with an increase of 86.3%and 142.1%,respectively.The average methane concentrations of Boreholes#9(4.05%)and#10(6.18%)were 64.6%and 151.2%higher than that of Borehole#8(2.46%),respectively.On the other hand,the dewatering ratio of Boreholes#9(4.36%)and#10(3.11%)was almost 19 times and 13 times greater than that of Borehole#8(0.22%).These field test results were in agreement with the experimental data.The significant increase in both methane concentration and dewatering ratio demonstrated that GWA technology could be applied for enhanced methane drainage in coal mines.Important lessons learned at Xinjing coal mine might be applied to other coal mines in China and elsewhere.

Monitoring Instrumentation in Underground Structures

Nowadays underground structures are very important. Based on observations of engineering;properties during geotechnical construction are an integral part of the design of underground structures. This research presents instrumentation as a tool to assist with these measurement observations, determine the need for modifications to loading or support arrangement. Also apart from above construction control, instrumentation is also indispensable for site investigation, design verification and safety of the structure. Instrumentation used in the construction of tunnels and subways can be implemented in three stagesbefore, during operation and during operation are examined. Metro Railway Tunnels are constructed in populated area and have a more comprehensive instrumentation and monitoring program that additionally includes monitoring of ground conditions, underground water levels, tilt and settlement of nearby buildings or other structures of interest in the vicinity of the tunnel alignment. Instrumentation monitoring for metro railway tunnels includes monitoring of the structures under construction together with the ground, buildings and other facilities within the predicted zone of influence. Furthermore, instrumentation and subway tunnels in and around them increase accuracy of the different layers of the earth and excavation of the surrounding structures and make safety and accuracy. This paper presents the features of sophisticated instrumentation available today for geotechnical monitoring. A wide range of sophistic have been described with their applications ted electronic and mechanical instrumentation with different instrumentation schemes used to meet the requirements of different types of structures.

基于双重介质渗流-应力耦合模型的高压压水试验渗透参数反演

高压压水试验过程中岩体易发生水力劈裂产生裂隙,岩体内部孔隙、裂隙双重导水,渗流场和应力场相互作用,导致岩体渗透参数的时空变异性。基于高压压水试验反演渗透参数需考虑双重介质渗流-应力耦合作用下产生裂隙前后渗透系数的变化规律,利用渗流-应力耦合数值模型结合工程现场高压压水试验数据进行参数反演,计算得到不同压力阶段下灰岩岩体渗透率。主要结论如下:发生水力劈裂前,随着注液压力的增大,渗透率及孔隙水压力在不同压力阶段之间分界明显,渗透率反演值与规程公式计算值相近;发生水力劈裂后,岩体渗透率增大约2倍,孔隙介质渗透率和通过的流量出现陡减现象。

鄂尔多斯盆地页岩油水力压裂试验场建设概述及实践认识

借鉴北美HFTS成功经验,长庆油田围绕进一步提高单井产量目标,整体规划了三期水力压裂试验场HFFL建设。I期于2022年启动,2024年完成,是国内首个完整意义上的水力压裂试验场。I期重点围绕夹层性页岩油长71、长72储层,坚持“压前地质工程一体化设计、压中测试响应反演拟合、压后取心验证分析评价”的研究路径,综合应用光纤、双井微地震、井下电视、示踪剂及取心等10项16井次测试,系统开展人工裂缝形态、多簇起裂及产液贡献率等精细评价,主要认识包括:(1)页岩油压后地下裂缝类型多样,300 m取心过程中累计发现裂缝431条,其中压裂缝115条、层理缝239条;(2)裂缝复杂程度远超预期,人工裂缝总量远大于簇数,局部未严格按照最大主应力方向扩展,受到岩性、天然裂缝发育等综合影响,裂缝存在明显偏转、沟通、弯曲等现象;(3)水力裂缝缝长延伸较长,缝高整体受控,支撑剂在取心岩屑中广泛分布,裂缝面同样观察到支撑;(4)多簇100%起裂,但扩展过程呈动态变化,砂液分配差异大,光纤评价均一指数平均61.8%;(5)长期产剖动态跟踪显示,生产6个月后,多裂缝段与优质甜点段贡献逐渐凸显。综上,水力试验场对长庆页岩油重新认识油藏、缝控储量、裂缝、产量提供了更加准确科学的理论依据,对井网优化、开发技术政策制定以及体积压裂优化设计都具有十分重要的作用,同时也为国内水力压裂试验场建设发挥了示范引领作用。

基于粘结单元法的干热岩储层水力压裂数值模拟与参数优化

水力压裂技术是实现低渗油气及地热储层的高效开发利用的关键技术手段,为了研究干热岩型地热储层水力压裂过程中水力裂缝的扩展规律,本文使用粘结单元法(Cohesive Zone Method,CZM)研究了压裂液排量、压裂液粘度以及水平地应力差对水力裂缝形态的影响,并利用正交试验对上述压裂工艺参数的组合进行优化。结果表明:压裂液排量对水力裂缝的长度具有重要影响,而压裂液的粘度对水力裂缝的宽度具有显著影响;压裂液的排量和粘度的增加,促进了分支裂缝的萌生和扩展;水平地应力差为1 MPa时,本文所建立的模型在压裂液排量和粘度分别取0.004 m3/s和0.07 Pa·s条件下,可获得最佳的压裂改造效果;随着压裂液的排量和粘度的持续增加,当压裂液的排量和粘度分别超过0.004 m3/s和0.07 Pa·s后,继续增加压裂液的排量和粘度将导致水力裂缝的长度和宽度的减小,可见在实际压裂过程中不能盲目通过提高压裂液的排量和粘度的方式实现对压裂效果的持续改进。本文丰富了干热岩储层改造的数值模拟手段,相关研究成果有望为干热岩型地热资源开采过程中裂缝扩展行为预测和压裂工艺参数的优化提供技术支撑。

旱涝急转工况下土石坝上游粘土防渗体水力劈裂研究

近年来作为极端小概率事件的旱涝急转工况频繁出现,极易造成防渗体缺陷扩展,诱发工程失事。通过在模型试验与数值计算分析的基础上探讨了旱涝急转工况下土石坝粘土防渗体中的水力劈裂问题。结果表明,旱涝急转工况中的干旱过程促使土体基质渗透性降低,同时导致防渗体产生裂缝,具备了发生水力劈裂的必要条件。理论分析推导了沿裂缝所在平面产生水力劈裂破坏的渗透压力理论值,离心试验模型测得铺盖层孔压骤降的同时砂层孔压骤增,表明裂缝受高水压作用产生劈裂贯穿了防渗体,裂缝处测量孔隙水压力值与理论推导结果基本一致。旱涝急转过程中裂缝处土体内的压应力先是逐渐增大,随后不断减小最终转变为拉应力,从而导致水力劈裂。研究结果对旱涝急转工况下的土石坝安全运行具有指导作用。

Hydraulic fracturing pressure of concentric double-layered cylinder in cohesive soil

This study aims to investigate hydrofracturing in double-layered soil through theoretical and experimental analysis,as multilayered soils where the difference in mechanical properties exists are generally encountered in practical engineering.First,an analytical solution for fracturing pressure in two different concentric regions of soil was presented based on the cavity expansion theory.Then,several triaxial hydraulic fracturing tests were carried out to validate the analytical solution.The comparison between the experimental and analytical results indicates the remarkable accuracy of the derived formula,and the following conclusions were also obtained.First,there is a linear relationship between the fracturing pressure and confining pressure in concentric double-layered cohesive soil.Second,when the internal-layer soil is softer than the external-layer soil,the presence of internal soil on the fracturing pressure approximately brings the weakening effect,and the greater strength distinction between the two layers,the greater the weakening effect.Third,when the internal-layer soil is harder than the external-layer soil,the existence of the internal-layer soil has a strengthening effect on the fracturing pressure regardless of the proportion of internal-layer soil.Moreover,the influence of strength distinction between the two layers on the fracturing pressure is significant when the proportion of internal-layer soil is less than half,while it’s limited when the proportion is more than half.The proposed solution is potentially useful for geotechnical problems involving aspects of cohesive soil layering in a composite formation.

Characterizing hydraulic fractures in shale gas reservoirs using transient pressure tests

Hydraulic fracturing combined with horizontal drilling has been the technology that makes it possible to economically produce natural gas from unconventional shale gas or tight gas reservoirs.Hydraulic fracturing operations,in particular,multistage fracturing treatments along with horizontal wells in unconventional formations create complex fracture geometries or networks,which are difficult to characterize.The traditional analysis using a single vertical or horizontal fracture concept may be no longer applicable.Knowledge of these created fracture properties,such as their spatial distribution,extension and fracture areas,is essential information to evaluate stimulation results.However,there are currently few effective approaches available for quantifying hydraulic fractures in unconventional reservoirs.This work presents an unconventional gas reservoir simulator and its application to quantify hydraulic fractures in shale gas reservoirs using transient pressure data.The numerical model incorporates most known physical processes for gas production from unconventional reservoirs,including two-phase flow of liquid and gas,Klinkenberg effect,non-Darcy flow,and nonlinear adsorption.In addition,the model is able to handle various types and scales of fractures or heterogeneity using continuum,discrete or hybrid modeling approaches under different well production conditions of varying rate or pressure.Our modeling studies indicate that the most sensitive parameter of hydraulic fractures to early transient gas flow through extremely low permeability rock is actually the fracture-matrix contacting area,generated by fracturing stimulation.Based on this observation,it is possible to use transient pressure testing data to estimate the area of fractures generated from fracturing operations.We will conduct a series of modeling studies and present a methodology using typical transient pressure responses,simulated by the numerical model,to estimate fracture areas created or to quantity hydraulic fractures with traditional well testing technology.The type curves of pressure transients from this study can be used to quantify hydraulic fractures in field application.

岳南煤业煤层水压致裂瓦斯抽采技术研究

针对岳南煤业15#煤层渗透性差、瓦斯含量高、抽采效率低等问题,考虑采用水压致裂技术提高抽采率。首先通过地应力实测得出工作面最大主应力为水平应力,其值为17.9 MPa,方向角为N32.43°E,压裂裂纹扩展也沿此方向;压裂钻孔的影响范围为5~8,为保证抽采效果,将压裂抽采钻孔间距设置为5 m,压裂抽采4个月后,煤层瓦斯残存量降低至2.54 m~3/t,且抽采周期缩短了近3个月,保证了矿井的安全高效生产。

煤层水力压裂增透技术研究

针对低渗透高瓦斯煤层,为了强化煤层瓦斯抽采效果,对煤层水力压裂注水压力对压裂效果的影响进行了模拟分析,并通过现场试验验证了模拟结果。经模拟,水压的增大对煤岩压裂效果起到促进作用,19.5 MPa水压能使煤层产生良好的裂纹扩展效果。经现场试验验证,压裂后,初始瓦斯涌出量是自然抽采孔的4.49倍,瓦斯流量衰减系数由0.035 8 d^(-1)降低至0.008 34 d^(-1),瓦斯流量衰减降幅达到76.71%,煤层透气性系数最大提升约为原来的44倍,表明水力压裂增透技术具有良好的煤层促抽效果。