中国大陆科学钻探主孔声发射法现今地应力状态的确定

对中国大陆科学钻探主孔的岩心进行了声发射测量,确定了301～1531m深度的最大主应力。并与钻孔崩落法(深度1269～1655m)测量结果进行了对比,结果表明,声发射测量所得测值基本上落在钻孔崩落法测值的趋势线上,两种方法所得结果一致,说明测量结果可信。测量结果表明科学钻探主孔地应力大小随深度增加,在浅部301m最大主应力为13.4MPa,在深部1655m为55.2MPa。随深度的增加率为0.0279MPa/m。最大主应力方向为N54°±3.3°E,且方向不随深度变化。     

The tectonic regime in Italy inferred from borehole breakout data

In Italy, the horizontal stress directions are well constrained in many regions, but the tectonic regime is not well known because the stress magnitudes are unknown. Our intention is to improve the knowledge of crustal stress in Italy, both at shallow depth and in low seismicity areas. Therefore, we inferred the tectonic regime from the comparison between the depth of breakout occurrence and the physical properties of the rocks in 20 boreholes. The critical value of the maximum horizontal stress, for which the effective tangential stress at the borehole wall overcomes the rock strength to form breakouts, could be computed from rock strength and density. Comparing the theoretical stress distributions for different tectonic regimes with the depth distribution of breakout occurrence, it is possible to infer the tectonic regime that fits best to the breakout depth distribution. We investigated boreholes up to 6 km deep located in different tectonic environments over the Italian peninsula: the Po Plain, the Apenninic chain, the Adriatic foredeep and the Tyrrhenian Quaternary volcanic region. These wells are characterised by breakout data of good quality (A, B and C, according to World Stress Map quality ranking system). The results are in general agreement with the style of faulting derived from earthquake focal mechanisms and other stress indicators. Our results show a predominance of a normal faulting (NF) regime in the inner Apennines and both normal faulting and strike–slip faulting (SS) style in the surrounding regions, possibly also associated with changes in the tectonic regime with depth.     

下辽河坳陷现代应力场特征

本文通过辽河油田的钻孔崩落资料及小地震震源机制解，推断出辽河坳陷地区现代构造应力场的特征。两种方法得到的结果基本一致，即区域应务场和局部应力场的结果一致，该地区处于走滑断层型应力状态。     

中国大陆科学钻探主孔2000米以上脆性变形构造应力场

在主孔2000米之内，存在复杂的脆性破裂系统和构造应力场。根据其充填物的特征，可划分为由石英、方解石和绿泥石等矿物充填的微破裂，发育石英、方解石等矿物薄膜或擦痕线理的微破裂和既无矿物充填、也无矿物薄膜的微破裂等3种不同类型的脆性应变现象，它们依次代表早、中、晚和深、中、浅3个不同构造层次的脆性变形。初步分析表明脆性变形阶段存在有以南东东-北西西向为主导的挤压作用、北东-南西向的区域挤压作用、南北向挤压作用和垂向伸展作用等4期构造应力场。郯庐断裂东侧的现代构造应力场在区域上具有极大的稳定性。在脆性和脆-韧性转换带，制约苏鲁高压-超高压变质带侵位的主导应力作用方式为自南东东往北西西方向的挤压，它在时间和空间上具有一定的稳定性。     

Geology and hazard implications of the Maraunot notch in the Pinatubo Caldera,Philippines

The 1991 Pinatubo eruption left 5–6 km³ of debris on the volcano slopes, much of which has been mobilized into large lahars in the following rainy seasons. Also during the eruption, collapse, localized in part along preexisting faults, left a caldera 2.5 km in diameter that almost immediately began to accumulate a 1.6 × 10⁸ m³ lake. By 2001, the water had risen to the fault-controlled Maraunot Notch, the lowest, northwestern portion of the caldera rim comprising the physiographic sill of the Caldera Lake. That year, a narrow artificial canal dug into an old volcanic breccia underlying the outlet channel failed to induce a deliberate lake breakout, but discharge from heavy rains in July 2002 rapidly deepened the notch by 23 m, releasing an estimated 6.5 × 10⁷ m³ of lake water that bulked up into lahars with a volume well in excess of 1.6 × 10⁸ m³. Lakes in other volcanoes have experienced multiple breakouts, providing practical motivation for this study. Fieldwork and high-resolution digital elevation models reveal andesites and ancient lacustrine deposits, strongly fractured and deformed along a segment of the Maraunot Fault, a prominent, steeply dipping, left-lateral fault zone that trends N35°–40°W within and parallel to the notch. Seismicity in 1991 demonstrated that the Maraunot Fault is still active. The fault zone appears to have previously been the erosional locus for a large channel, filled with avalanche or landslide deposits of an earlier eruption that were exhumed by the 2002 breakout floods. The deformed lacustrine sediments, with an uncalibrated ¹⁴C age of 14,760 ± 40 year BP from a single charcoal sample, attest to the existence of an earlier lake, possibly within the Tayawan Caldera, rim remnants of which survive as arcuate escarpments. That lake may well have experienced one or more ancient breakouts as well. The 2002 event greatly reduced the possibility of another such event by scouring away the erodible breccia, leaving less erodible fractured andesites and lacustrine rocks, and by enlarging the outlet channel and its discharge capacity. Several lines of evidence indicate, however, that future lahar-generating lake breakouts at the notch may keep populations of Botolan municipality downstream at risk: (1) a volume of 9.5 × 10⁷ m³ of lake water remains perched 0.8 km above sea level; (2) seismicity in 1991 demonstrated that the Maraunot Fault is still active and movements of sufficient magnitude could enlarge the outlet and the discharge through it; (3) more likely, however, with or without earthquake activity, landslides from the steep to overhanging channel walls could block the channel again, and a major rainstorm could then cause a rise in lake level and sudden breakouts; (4) intrusion of a new dome into the bottom of the lake, possibly accompanied by phreatic explosions, could expel large volumes of lahar-generating water.     

Effect of fluid pressure on rock compressive failure in a nearly impermeable crystalline rock: Implication on mechanism of borehole breakouts

We conducted laboratory true triaxial experiments in the nearly impermeable Pohang rhyolite to investigate failure mechanisms under ‘dry’ and ‘wet’ rock conditions. Under ‘dry’ conditions prismatic specimens were jacketed all around to prevent confining fluid penetration. Under ‘wet’ conditions one pair of the specimen faces was left unjacketed and in direct contact with the confining fluid (kerosene) applying the least principal stress in an attempt to simulate the case of an unlined borehole wall. In both testing setups the true triaxial compressive strength for a given least principal stress increases significantly as the intermediate principal stress rises. The unjacketed rhyolite strength is, however, only 60 to 85% of the strength under dry conditions, depending on the magnitude of the intermediate principal stress. In dry rhyolite the failure process begins upon dilatancy onset, followed by microcrack localization, and ending in a steeply dipping shear fracture. On the other hand, brittle fracture in wet specimens occurs almost immediately after the onset of dilatancy by the development of one or more through-going extensile fractures subparallel and adjacent to one of the unjacketed faces, resembling the extensile cracks leading to borehole breakouts in crystalline rocks. We infer that upon dilatancy the confining fluid intrudes and quickly propagates newly opened stress-induced microcracks subparallel to the unjacketed faces, leading to ‘early’ failure.     

辽河油田大民屯凹陷井壁崩落法地应力测量

文中介绍了井壁崩落法地应力测量的基本原理和方法 ,并利用此方法对辽河油田大民屯凹陷地区 15口井的地层倾角测井资料进行了统计和分析 ,绘制了崩落椭圆长轴优势方位图。结果表明 ,该地区井壁崩落椭圆的长轴优势方位为 35 0°～ 10° ,由此确定的最大主应力方向为 80°～ 10 0° ,平均为 90° ,与用震源机制解得出的结果基本相符 ,说明该地区的构造应力场方向比较稳定 ,处于同一构造应力场的作用之下     

The present-day stress field of New South Wales,Australia

The Australian continent displays the most complex pattern of present-day tectonic stress observed in any major continental area. Although plate boundary forces provide a well-established control on the large-scale (>500 km) orientation of maximum horizontal stress (S_Hmax), smaller-scale variations, caused by local forces, are poorly understood in Australia. Prior to this study, the World Stress Map database contained 101 S_Hmax orientation measurements for New South Wales (NSW), Australia, with the bulk of the data coming from shallow engineering tests in the Sydney Basin. In this study we interpret present-day stress indicators analysed from 58.6 km of borehole image logs in 135 coal-seam gas and petroleum wells in different sedimentary basins of NSW, including the Gunnedah, Clarence-Moreton, Sydney, Gloucester, Darling and Bowen–Surat basins. This study provides a refined stress map of NSW, with a total of 340 (A–E quality) S_Hmax orientations consisting of 186 stress indicators from borehole breakouts, 69 stress measurements from shallow engineering methods, 48 stress indicators from drilling-induced fractures, and 37 stress indicators from earthquake focal mechanism solutions. We define seven stress provinces throughout NSW and determine the mean orientation of the S_Hmax for each stress province. The results show that the S_Hmax is variable across the state, but broadly ranges from NE–SW to ESE–WNW. The S_Hmax is approximately E–W to ESE–WNW in the Darling Basin and Southeastern Seismogenic Zone that covers the west and south of NSW, respectively. However, the present-day S_Hmax rotates across the northeastern part of NSW, from approximately NE–SW in the South Sydney and Gloucester basins to ENE–WSW in the North Sydney, Clarence-Moreton and Gunnedah basins. Comparisons between the observed S_Hmax orientations and Australian stress models in the available literature reveal that previous numerical models were unable to satisfactorily predict the state of stress in NSW. Although clear regional present-day stress trends exist in NSW, there are also large perturbations observed locally within most stress provinces that demonstrate the significant control on local intraplate sources of stress. Local S_Hmax perturbations are interpreted to be due to basement topography, basin geometry, lithological contrasts, igneous intrusions, faults and fractures. Understanding and predicting local stress perturbations has major implications for determining the most productive fractures in petroleum systems, and for modelling the propagation direction and vertical height growth of induced hydraulic fractures in simulation of unconventional reservoirs.     

Borehole image analysis of the Nankai Accretionary Wedge, ODP Leg 196: Structural and stress studies

Electrical images recorded with Resistivity-At-Bit (RAB) from two sites drilled during Ocean Drilling Program (ODP) Leg 196 were analyzed to study the effects of subduction at the Nankai margin. For the first time in the history of scientific deep-sea drilling in ODP, in situ complete borehole images of the décollement zone were obtained. Analyses of all drilling-induced fracture data indicated that the maximum horizontal compressive stress (S_Hmax) axes have an azimuth of 303°, and analyses of breakout data from RAB images indicated an azimuth of 310°. These azimuths approximate the convergence direction of the Philippine Sea plate towards the Eurasian plate. The frontal thrust at Site 808 was encountered at about 389 mbsf. Density, porosity, resistivity, and gamma ray data change across the frontal thrust. The décollement zone at the deformation front was identified between 937 and 965 mbsf. The base of the décollement is sharply defined as the maximum extent of conductive fracturing and is marked by abrupt changes in physical properties [Mikada, H., Becker, K., Moore, J.C., Klaus, A., Austin, G.L., Bangs, N.L., Bourlange, S., Broilliard, J., Brückmann, W., Corn, E.R., Davis, E.E., Flemings, P.B., Goldberg, D.B., Gulick, S.S., Hansen, M.B., Hayward, N., Hills, D.J., Hunze, S., Ienaga, M., Ishiguro, H., Kinoshita, M., Macdonald, R.D., McNeill, L., Obana, S., Hong, O.S., Peacock, S., Pettigrew, T.L., Saito, S., Sawa, T., Thaiprasert, N., Tobin, H.J., Tsurumi, H., 2002. Proc. ODP, Initial Rep., 196, College Station, TX, (Ocean Drilling Program)]. The upper boundary of the décollement is marked by several sets of conductive fractures and by high variability in physical properties. The décollement zone is characterized by intense brittle fracturing. These fractures are considered to be the consequence of cyclic stresses and high fluid pressures in this zone. We analyzed fracture dips and their orientations at both sites and found that they are all consistent with a unique stress field model surrounding the two sites.     

用于防雷工程的电涌保护器的测试研究

针对电源类电涌保护器的试验可进行分类,电源保护器的测试方法除了有规范的要求外,还有许多具体的问题需要研究解决。针对SPD测试中出现的问题进行分析,主要围绕M OV电阻片的漏电流与相关测试所出现的现象进行讨论,对击穿、闪络、燃烧问题进行研究,归纳了现今电涌保护器最常出现的问题。