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.

     

An explicit method for numerical simulation of wave equations

In this paper, a method to develop a hierarchy of explicit recursion formulas for numerical simulation in an irregular grid for scalar wave equations is presented and its accuracy is illustrated via 2-D and 1-D models. Approaches to develop the stable formulas which are of 2M-order accuracy in both time and space with M being a positive integer for regular grids are discussed and illustrated by constructing the second order (M = 1) and the fourth order (M = 2) recursion formulas.     

Investigation of ionospheric TEC changes related to the 2008 Wenchuan earthquake based on statistic analysis and signal detection

Ionospheric TEC (total electron content) time series are derived from GPS measurements at 13 stations around the epicenter of the 2008 Wenchuan earthquake. Defining anomaly bounds for a sliding window by quartile and 2-standard deviation of TEC values, this paper analyzed the characteristics of ionospheric changes before and after the destructive event. The Neyman-Pearson signal detection method is employed to compute the probabilities of TEC abnormalities. Result shows that one week before the Wenchuan earthquake, ionospheric TEC over the epicenter and its vicinities displays obvious abnormal disturbances, most of which are positive anomalies. The largest TEC abnormal changes appeared on May 9, three days prior to the seismic event. Signal detection shows that the largest possibility of TEC abnormity on May 9 is 50.74%, indicating that ionospheric abnormities three days before the main shock are likely related to the preparation process of the M_S8.0 Wenchuan earthquake.     

旅游空间营造的理论与实例探析——以重庆三峡广场为例

尽管研究旅游空间已有多年历史,但从景观、建筑、游憩的角度入手并不多见.在此基础上,探讨旅游空间营造的基本理论.首先,从图底理论、联系理论、场所理论的角度构思了旅游空间营造的设想;其次,指出旅游空间营造的核心理念--场所精神,并对其影响因素作了详细的分析;第三,从物质性空间与非物质性空间出发,深入解剖重庆三峡广场旅游空间营造的具体内容;最后,对旅游空间可持续发展作出展望.     

喀斯特山区不同复种指数条件下的土壤质量变化——以普定县猫洞小流域为例

选择贵州中部喀斯特山区普定县猫洞小流域地区,通过长期受不同生产行为影响的区域（低复种旱作区、高复种旱作区、高复种复合农作区）的土壤采样分析,结果表明:喀斯特山区小流域土壤在长期不同生产行为影响下,从低复种指数旱作区、高复种指数旱作区到高复种指数复合农作区,土壤容重、粘粒含量减小,而土壤有机质、腐殖酸含量、全氮、碱解氮、速效磷、速效钾、土壤呼吸强度、脲酶、磷酸酶、蛋白酶活性含量依次增大,土壤全钾含量和过氧化氢酶活性却依次减小。聚类分析结果进一步表明:高复种复合农作区土壤保肥、保水、供肥等状况最好;而低复种旱作区土壤质量和供肥、保肥、保水等性状最差。上述结果说明,农户的不同生产行为对土壤质量有一定的影响。      

从5.12汶川地震前后分量应变仪观测到的应变异常看建设密集应变观测网络的必要性

2004年我国“数字地震观测网络工程”决定在我国布设40套YRY-4型四分量钻孔应变仪。本文介绍5·12汶川地震前后分量应变仪观测到的应变异常及根据应变异常与其它观测手段对8·30会理6.1级地震较准确的预测。据此,提出我国有必要加速应变密集台网建设。     

Paleoproterozoic granitic gneisses of the Dinggye and LhagoiKangri areas from the higher and northern Himalaya, Tibet: Geochronology and implications

Granitic gneisses have been widely found in crystalline rocks in the Dinggye area of the Higher Himalaya (HHM) and the LhagoiKangri area of the North Himalaya (NHM), Tibet. In the HHM, the gneisses intruded in the granulite-amphibolite facies metamorphosed sedimentary rocks, known as Nyalam group. In the NHM, the gneisses intruded in the amphibolite facies metamorphosed ones, known as LhagoiKangri group. These granitic gneisses are peraluminous monzonitic granites in terms of their mineral assemblage, and are considered as being derived from metamorphosed sedimentary rocks by anatexis based on the transitional relationship of the gneisses with their migmatitized wall rocks. Zircons are similar in crystal shape and interior structure from both gneisses. Most of them are euhedral or subhedral elongated prism-shaped transparent crystals, with fine oscillatory zoning, showing the magmatic genesis. Some of them are short prism-shaped and with relict core inherited from magma source and oscillatory zoning mantle crystallized from magma. SHRIMP U-Pb dating of zicons shows that both the granitic gneisses in the HHM and NHM are Paleoproterozoic (1811.6±2.9 Ma and 1811.7±7.2 Ma, respectively). These ages are similar to those (1815 to 2120 Ma) from granitic gneiss which is widely distributed in the Lesser Himalaya (LHM). The ages of inherited zircons (>2493.9±7.0 Ma, 2095.8± 8.8 Ma, 1874±29 Ma) exhibit the possible presence of several thermal events in Paleoproterozoic. All of the ages suggest the same India basement beneath the different units in Himalaya area, and do not support the idea that the HHM and NHM are accretionary terranes in Pan-Africa orogenic event. The fact that the basement in HHM is as old as or even younger than LHM is inconsistent with the presently prevalent orogenic models such as either extrusion of low-viscosity mid-crust or orogenic channel.     

九龙江口磷的界面分配和转移

１９９２年８月航次调查结果表明，九龙江口水体中磷的迁移呈保守行为，ＴＰ和ＰＰ含量随着海水盐度的降低呈增加趋势，ＤＰ含量刚好相反；Ｓ〈１５的低盐区，盐度对磷迁移的影响比较显著。     

Influence of Kinematic Analysis Parameters of Drag Anchor Trajectory Prediction Using Yield Envelope Method

Drag anchor is widely applied in offshore engineering for offshore mooring systems. The prediction of the invisible trajectory during its drag-in installation is challenging for anchor design in determining the anchor final position for ensuring sufficient holding capacity. The yield envelope method based on deep anchor failure for kinematic analysis was proposed as a promising trajectory prediction method for drag anchor. However, there is a lack of analysis on the effects of the parameters applied in the kinematic analysis. The current work studies the effects of the yield envelope parameters, anchor line bearing capacity factor and the anchor/soil interface friction. It is found that the accuracy of the yield envelope parameters has large impact on the prediction results based on deep yield envelopes.Analyses of cases with smooth fluke predict deeper embedment depth than that from analyses of cases with rough fluke. The decrease of the capacity factor results in the increase of the anchor embedment depth, the anchor line load,the anchor chain angle and the stable value of the normalized horizontal load component for the same drag length,while the stable value of the normalized vertical load component decreases when the capacity factor decreases. This illustrates the importance in applying reasonable parameters and improving the method for more reliable prediction of the anchor trajectory.     

三种断层位移测量工具对比分析

基于构造地貌对活动断层进行定量研究对理解断层活动习性及预测其将来的活动行为具有重要的意义。目前人们对断层位错的获取主要采取软件测量的方式,因此对断层位错测量工具的可靠性及应用性的分析至关重要。文章首先对3种常用的测量工具LaDicaoz、3D＿Fault＿Offsets与MCSST进行介绍;然后,基于无人机摄影航测获得的党河水库断裂高精度DEM以及无人机机载LiDAR获取的西秦岭北缘断裂黄香沟段高精度DEM,使用MCSST对党河水库断裂进行详细的陡坎垂直位错测量,利用LaDicaoz和3D＿Fault＿Offsets对黄香沟断裂进行精细的水平位错测量,并通过交叉检验方法对这3种测量工具的可靠性进行分析;最后,基于不同性质断裂位移的提取过程和结果,对这3款软件的自动化程度、使用难易程度及可重复性等特性进行综合对比分析,并总结3种工具的优势与不足。研究结果表明,LaDicaoz和3D＿Fault＿Offsets在水平位移提取方面具有较高精度和较好应用,MCSST在垂直位移提取及分析上应用较好,但3种工具的自动化程度皆存在不足,工具间的相互借鉴并将人工智能引入将成为进一步提高测量软件科学性与...