成像测井缝洞解释评价研究进展

综合露头刻度井、数值模拟和物理模拟的实验结果对微电阻率扫描成像测井缝洞解释评价的研究进展进行了总结和探讨,分别包括岩芯归位、缝洞刻度率、岩芯和成像裂缝参数的差异性,以及裂缝宽度和地层孔隙度的计算。岩芯归位确定了缝洞体在地层中的深度和方位。电成像测井对过井眼未充填缝和孔洞发育段的刻度率为100%,而单个孔洞在岩芯和电成像测井中通常无法一一对应。单条裂缝的倾角或井周长度在岩芯和成像测井中具有较高的相关性,而裂缝宽度的相关性一般。数模和物模的结果表明电成像测井裂缝宽度的计算受多种因素影响,当裂缝的视宽度大于0.1 mm时,电成像测井计算的裂缝宽度和裂缝视宽度基本一致,当小于0.1 mm时,电成像测井计算的宽度值误差较大。目前电成像测井通过孔隙度谱法和图像分割法计算地层的孔隙度,但都受限于除孔洞的其他低阻地质体的影响,因此需要加强岩芯刻度的功能。     

同韧性剪切断裂特征及其研究意义

同韧性剪切断裂是一种新的断裂类型,它既不同于脆性断裂,也不同于韧性剪切带。它是韧性剪切带在一定条件下发展到一定程度转化为宏观破裂的产物,在宏观、微观、地球化学等许多方面独具特征。它的研究对丰富和发展构造地质学理论、地质找矿、地震、地质灾害、工程稳定等许多方面有重要意义。     

准噶尔盆地玛湖凹陷二叠系风城组页岩储集层裂缝测井识别与有效性分析*

中国页岩油资源潜力巨大,裂缝的发育程度是影响页岩油产量高低的重要因素。以准噶尔盆地玛湖凹陷风城组页岩储集层为研究对象,通过岩心观察、薄片鉴定、常规及成像测井方法总结归纳了研究区裂缝的发育特征,提出“常规+成像+岩心”的页岩储集层裂缝测井综合识别方法,建立了典型裂缝发育类型的测井综合识别图版。结果表明,玛湖地区天然裂缝在风三段密集发育,风一段次之,风二段中部几乎不发育。裂缝主要在长英质页岩、云质页岩和混合质页岩中发育,以高角度构造裂缝与低角度成岩裂缝为主,开启程度高,少数被碳酸盐矿物充填,走向主要为NW-SE向。基于裂缝参数定量计算结果,结合岩性及矿物组分和地应力等因素分析了储集层裂缝有效性。研究认为,脆性矿物组分含量高、走向平行于现今水平最大主应力的高角度未充填裂缝发育段对储集层有效性存在明显的控制作用,与产液资料较为吻合。此裂缝测井综合评价方法效果显著,可为页岩储集层裂缝识别与有效性评价提供方法支撑。     

Aligned fractures in carbonate rocks: laboratory and in situ measurements of seismic anisotropy

By vertical seismic profiling and shear wave analysis we show that a packet of carbonate reservoir rocks, found at nearly 3000 m depth in the North German Basin, is seismically anisotropic. For vertical paths of wave propagation the estimated velocity difference of the split shear waves is 10%. No shear wave birefrigence is observed within the hangingwall which, therefore, has to be regarded as isotropic or transversely isotropic. Additional laboratory investigations of the petrography of drilled carbonate samples and of their seismic velocities show that the anisotropy is most probably caused by subvertical fractures with preferred azimuthal orientation. The strike direction of the aligned fractures determined by analysis of split shear waves is approximately N55°E. This value agrees with recently published directions of maximum horizontal tectonic stress in pre-Zechstein sediments in the eastern part of the North German Basin, but it is in contrast to the world stress map. Received: 20 April 1999 / Accepted: 25 August 1999     

Variations in thickness of fault‐controlled dikes and its implications: A case study of Gosung area,South‐East Korea

Dikes are natural records that can be used to understand the way magma flows in the crust. Coastal platform outcrops in Gosung, South Korea, show clear evidences that their intrusion took place along pre‐existing fractures. We analyzed outcropping dikes, measuring variations in dike thickness as well as fracture density (cumulative number of fractures along strike) and geometry around the dikes. The geometry and thickness variations of dikes intruded along pre‐existing fractures can be interpreted to understand the effect of pre‐existing fractures to evolution on magma flow, especially related with fault damage zones. This helps us to gain a better understanding of magma and fluid flow along pre‐existing fractures. Magma flow is greater along planes that strike perpendicular to the direction of least compressive horizontal stress, and along well connected fractures that show a high degree of connectivity. At the fault tip and linkage damage zone, there is a concentration of extensional fractures; in these areas injected dikelets can form. As faults become linked, the fracture density increases, until they become fully linked and act as one through‐going fault plane. As faults evolve, the boundary conditions of the faults vary and this has an impact on dike characteristics. Fracture geometry around dikes that intruded pre‐existing faults can be used as a record of fault evolution and this can give insights into how the maturity of a fault system can affect to the related magma or fluid flow characteristics.     

Structures and facies associated with the flow of subaerial basaltic lava into a deep freshwater lake: The Sulphur Creek lava flow, North Cascades, Washington

The ca. 8800 ¹⁴C yrs BP Sulphur Creek lava flowed eastward 12 km from the Schriebers Meadow cinder cone into the Baker River valley, on the southeast flank of Mount Baker volcano. The compositionally-zoned basaltic to basaltic andesite lava entered, crossed and partially filled the 2-km-wide and > 100-m-deep early Holocene remnant of Glacial Lake Baker. The valley is now submerged beneath a reservoir, but seasonal drawdown permits study of the distal entrant lava. As a lava volume that may have been as much as 180 × 10⁶ m³ entered the lake, the flow invaded the lacustrine sequence and extended to the opposite (east) side of the drowned Baker River valley. The volume and mobility of the lava can be attributed to a high flux rate, a prolonged eruption, or both. Basalt exposed below the former level of the remnant glacial lake is glassy or microcrystalline and sparsely vesicular, with pervasive hackly or blocky fractures. Together with pseudopillow fractures, these features reflect fracturing normal to penetrative thermal fronts and quenching by water. A fine-grained hyaloclastite facies was probably formed during quench fragmentation or isolated magma-water explosions. Although the structures closely resemble those developed in lava-ice contact environments, establishing the depositional environment for lava exhibiting similar intense fracturing should be confirmed by geologic evidence rather than by internal structure alone. The lava also invaded the lacustrine sequence, forming varieties of peperite, including sills that are conformable within the invaded strata and resemble volcaniclastic breccias. The peperite is generally fragmental and clast- or matrix-supported; fine-grained and rounded fluidal margins occur locally. The lava formed a thickened subaqueous plug that, as the lake drained in the mid-Holocene, was exposed to erosion. The Baker River then cut a 52-m-deep gorge through the shattered, highly erodible basalt.     

Importance of fracturing during retro-metamorphism of eclogites

Presented textural and petrological data show that the deep to intermediate continental crust may fracture and that microfractures are the locus of fluid and mass transfer necessary for retrograde metamorphism. Kyanite eclogites from Ulsteinvik, Norway, underwent partial retrogression to granulite and amphibolite facies assemblages during near-isothermal exhumation from depths equivalent to more than 2.0 GPa at temperatures of 700–800 °C. Plagioclase-bearing assemblages, rich in hydrous phases, formed along margins of eclogite lenses and along mesoscopic fracture systems. Hydrated zones are from 1–50 cm thick, with adjacent wall-rock eclogite replaced by symplectites. At a low degree of reaction, the secondary minerals in the wall-rock are found along intra- and intergranular microfractures (typically 50–100 μm wide). Minerals filling the microfractures include orthopyroxene–plagioclase–spinel in garnet; plagioclase–sapphirine, plagioclase–corundum and plagioclase–spinel in kyanite; and diopside–plagioclase in omphacite. The microfractures are often arranged en echelon and are connected through microfaults. Releasing bends filled with amphibole and spinel form along microfaults in garnet. The faulting and fracturing caused localized chemical change in garnet: the damage zones close to faults are enriched in FeO and MnO with steep compositional gradients (8 wt% FeO over <20 μm). These FeO- and MnO-enriched zones form wedge-like structures around the tip of the faults (horsetail structures) and rose- or flame-like structures at sticking points along faults. They may represent examples of stress-induced chemical transport during fracture propagation. The change from dry to amphibole-bearing assemblages at the tip of the fracture, and fractures ending in splays of fluid inclusions trails, reflect the involvement of a fluid phase during fracture propagation. This suggests that the ‘dry’ granulite facies retrogression was also driven by fluid infiltration and that metamorphism at depth in collision zones may not be controlled by pressure and temperature alone.     

新集煤层气开发试验井水力压裂增产改造

根据新集试验区地质、储层条件,提出了适合该地区煤层气井水力压裂选井选层方法。通过对3口试验井8个目标层段进行水力压裂增产改造,认为活性水压裂液、兰州砂支撑剂应作为该地区的首选压裂液和支撑剂。利用先进的压裂软件进行压裂设计、实时分析以及压后评价,通过严密组织、合理施工获得了单井最大日产气量3 278m3/d,为该地区今后进行煤层气勘探开发提供了技术基础。      

白鹤滩水电站坝区深部破裂岩体地应力演化特征

还原深部破裂岩体赋存地应力场演化过程,研究深部破裂岩体成因、形成年代及发展演化趋势。以岩体深部破裂特征为基础,结合构造演化、河谷演化及浅生改造理论,采用数值模拟方法,从地应力场变化及应变能释放角度解释深部破裂形成演化过程。研究表明,宽谷期大规模夷平作用使深部破裂赋存应力场发生根本性改变,与现今应力场趋于一致,但并未导致深部破裂形成;侧向卸荷是深部破裂形成的主要原因,侧向卸荷导致主应力减小,但方向维持不变,当侧向临空面出现,伴随应变能释放,NW向结构面拉张形成具有继承性的NW向深部破裂;错动带的差异回弹形成残余拉应力,导致NE向新生性深部破裂形成;深部破裂形成地质年代应大致对应于Ⅲ级阶地形成初期,即Q2晚期～Q3早期阶段