聚合物凝胶堵漏剂在大裂隙溶洞地层中的研究及应用

广东河源地区地质条件复杂,溶洞、裂隙十分发育。钻探生产中施工难度大,导致在钻孔施工中冲洗液漏失严重,施工周期长,成本高。针对该地区大裂隙溶洞地层研制的一种新型聚合物凝胶堵漏剂,从理论上探讨该新型凝胶堵漏剂的基本性能和作用机理,还通过室内试验与现场测试对凝胶堵漏剂进行研究,测试了凝胶堵漏剂的成胶时间、承压能力、破胶性能等。并针对凝胶堵漏材料的配方进行了对比试验,得出了现场的最佳应用配方,对漏失地层进行堵漏,取得了良好的效果,降低了钻井液的消耗,提高了钻井效率。广东河源地区的应用表明,所研制新型凝胶堵漏剂具有良好的流动性且成胶时间较短,符合生产需要,同时还具有很强的承压堵漏能力,破胶性能显著,不会卡住钻具。该新型堵漏剂对广东河源地区的堵漏施工效果较好,易于配制、调整,不需要特殊设备,对大裂隙溶洞地区的堵漏具有很好的推广应用前景。     

Appraisal of fracture sampling methods and a new workflow to characterise heterogeneous fracture networks at outcrop

Characterising fractures at outcrop for use as analogues to fractured reservoirs can use several methods. Four important fracture data collection methods are linear scanline sampling, areal sampling, window sampling and circular scanline sampling. In regions of homogeneous fracture networks these methods are adequate to characterise fracture patterns for use as outcrop analogues, however where fractures are heterogeneous, it is more difficult to characterise fracture networks and a different approach is needed.We develop a workflow for fracture data collection in a region of heterogeneous fractures in a fold and thrust belt, which we believe has applicability to a wide variety of fracture networks in different tectonic settings. We use an augmented circular scanline method, along with areal sampling to collect a range of fracture attribute data, including orientation, length, aperture, spatial distribution and intensity. This augmented circular scanline method more than halves the time taken for data collection, provides accurate, unbiased data that is representative of local fracture network attributes and involves data collection of a wider range of fracture attributes than other sampling techniques alone.     

Impact of textural patterns on modeled rock weathering rates and size distribution of weathered grains

Rock texture has a critical influence on the way rocks weather. The most important textural factors affecting weathering are grain size and the presence of cracks and stylolites. These discontinuities operate as planes of mechanical weakness at which chemical weathering is enhanced. However, it is unclear how different rock textures impact weathering rates and the size of weathered grains. Here, we use a numerical model to simulate weathering of rocks possessing grain boundaries, cracks, and stylolites. We ran simulations with either synthetic or natural patterns of discontinuities. We found that for all patterns, weathering rates increase with discontinuity density. When the density was <~25%, the weathering rate of synthetic patterns followed the order: grid > honeycomb > Voronoi > brick wall. For higher values, all weathering rates were similar. We also found that weathering rates decreased as the tortuosity of the pattern increased. Moreover, we show that textural patterns strongly impact the size distributions of detached grains. Rocks with an initial monomodal grain size distribution produce weathered fragments that are normally distributed. In contrast, rocks with an initial log-normal size distribution produce weathered grains that are log-normally distributed. For the natural patterns, weathering produced lower modality distributions.     

New Insights into the Origin of Kabbaldurga Charnockites, Karnataka, South India

A detailed study of the structure and petrology of the rocks bordering the Kabbaldurga-type charnockites provides important constraints on the origin of these charnockites. The structural elements register three phases of deformation and show a uniform pattern in the larger area, a pattern consistent with the regional structure of the Precambrian of Southern Karnataka. In the Kabbaldurga area, however, some of the earlier structures are poorly preserved. Yet there are vestiges of early folds described by banded/layered charnockites as in the neighbouring Kodamballi area, and a consistent development of dilatant structures which can be related to the kinematics of deformation in the larger terrain. At Kabbaldurga the pegmatitic charnockites occur as veins of diverse orientation; but they rarely follow the shear - generated structures.

The metamorphic reactions invoked by previous workers to explain in situ transformation of gneiss to charnockite were based on chemical similarity of some close pairs. But the petrographic and chemical variations in the pegmatitic charnockites and the Peninsular gneisses at Kabbaldurga quarry are compelling features which cannot be explained by the hypothesis of in situ transformation. We have argued, on the basis of rock and mineral chemistry, that derivation of the pegmatitic charnockites by dehydration melting in metabasites offers a better explanation. Pressure-temperature values (at least 850° to 900° C, 7 kbar) obtained by us for the granulites of this area, viewed against the results of experimental dehydration melting in basic rocks with hornblende and/or biotite, provide strong support for this model. In the field leucosomes within the basic granulites of Kabbaldurga are not uncommon. The compositions of the pegmatitic charnockites (tonalitic and granitic) match those of the melts produced in experiments. Further, the pattern of variation in the composition of hornblende and plagioclase in the basic granulites of the Kabbaldurga area is compatible with extraction of melts. This alternative model for the origin of the Kabbaldurga charnockites is petrologically feasible and does not require either in situ transformation or structurally controlled growth, which, incidentally, are not ubiquitous at Kabbaldurga     

An In-situ Experimental Study of Fractures Network Identification within Bedrock by High-density Electrical Resistivity Tomography

对于以低渗透性基岩为处置围岩的核废物地质处置库来说,基岩中的裂隙网络是地下水进入处置库和放射性核素从处置库向外界环境迁移的主要通道.因此,研究基岩内裂隙网络的空间分布特征,对核废物的地质处置是否安全具有十分重要的意义.本文以花岗岩为例通过野外试验,分析研究了利用高密度电阻率成像法(ERT),对处于不同状态条件下的基岩中裂隙网络进行三维原位识别的效果及能力.结果表明在以高阻值为主要电特性的基岩中,利用ERT对基岩中三维裂隙网络进行原位识别是可行的,并且裂隙的电阻率特征能较好的反映出裂隙的空间分布位置和形态,但对裂隙网络识别的效果与测线方向有关.     

四川盆地梓潼地区须家河组储集层裂缝特征及控制因素

基于野外露头、岩心、薄片及样品实验测试等资料, 对四川盆地梓潼地区须家河组储集层裂缝特征与控制因素进行了精细分析与解释。须家河组致密砂岩储集层主要发育3种类型的裂缝, 分别为构造裂缝、成岩裂缝以及与异常流体高压有关的裂缝, 并以构造裂缝为主。裂缝走向主要为近东西向、近南北向和北西向, 平均密度0.56条/m, 多为层内发育。平面上, 沿老关庙—文兴场—柘坝场构造, 裂缝密度依次减小; 纵向上, 以须四段裂缝最为发育。有效裂缝比例在老关庙地区最低, 向北东至柘坝场构造呈带状递增趋势。该区储集层裂缝的分布主要受岩性、岩层厚度、构造部位及异常流体压力等因素控制, 其中断层对裂缝分布的控制作用最为显著。细粒级、薄层砂岩更容易产生裂缝, 断裂带附近与构造高部位也是该区裂缝发育的有利区域, 且断层对裂缝的控制作用远大于构造高部位的影响作用。此外, 异常流体高压的存在也有利于该区裂缝的发育, 尤其是张裂缝, 其密度在高压区明显增大; 异常高压也能导致早期闭合缝重新开启, 并且对裂缝中矿物的充填程度与溶蚀强度有重要的控制作用。      

迪北气田三维探区下侏罗统阿合组裂缝定量预测

塔里木盆地库车坳陷的下侏罗统阿合组低孔低渗砂岩是迪北气田的主要油气储集层,构造裂缝作为油气运移通道和储集空间,其发育特征和分布规律是制约油气勘探开发的关键。本次研究采用迪北气田最新的三维构造图,考虑区域地质背景、地层起伏、断层分布等诸多因素,将目的层下侏罗统阿合组分为3段,基于实测岩石力学参数,利用三维弹性有限元数值模拟方法,计算获得的库车坳陷新近纪构造应力场的大小、方向与实测应力感数据比较吻合。以此构造应力场为基础,在迪北地区11口井的约束下,用岩石破裂值和应变能密度构建起的“二元法”对阿合组每一层段的裂缝密度分布规律进行预测。结果表明：平面上,迪北斜坡带的依南2-迪西1-迪北104区域、迪北101-依南5以南区域和吐孜1井以西-吐孜3井以北的区域为裂缝相对发育区;垂向上,阿合组中下段要比上段裂缝更为发育。该构造裂缝预测结果对迪北气田致密砂岩储层的勘探开发提供了新的参考依据。