惠民凹陷基山砂体成岩作用及对油气圈闭的影响

惠民凹陷基山砂体成岩作用对岩性地层圈闭的形成具有重要的控制作用。通过砂体储层结构和成岩作用分析发现,半径在0.4μm～1.5μm之间的孔喉占累计渗透率贡献值达到90%。分析表明,基山砂体主要储集空间为次生孔隙,主要是由长石等陆源碎屑矿物蚀变而成的自生高岭石晶间微孔,其孔径与压汞分析测试值吻合较好,是与之对应的岩石主要储集空间。压实作用造成的岩石物性致密带和沿砂体边缘形成的碳酸盐胶结层,构成了成藏组合中的区域盖层和局部盖层。即受成岩作用控制,基山砂体层段内致密胶结层和次生孔隙带为油气圈闭提供了有效的储盖组合。这说明成岩作用可以作为相对独立的因素控制油藏的圈闭条件,成岩相研究是连接油藏、圈闭和成岩现象的基本桥梁。     

Dewatering effects on the erodibility of newly deposited cohesive beds by unidirectional currents

A series of laboratory experiments on cohesive sediments under inorganic conditions was undertaken in order to evaluate the impact of fluid bed shear stress on the build-up of bed resistance to erosion with time. The importance of small pressures due to flowing water to increase bed strength is presented. It is also shown that the susceptibility of a cohesive bed to changes in its erodibility is related to deposited bed thickness due to sediment disturbance caused by dewatering from the consolidating bed. Laboratory experiments that use beds deposited from suspension should thus report the thickness of the bed prior to resuspension.     

Is anthropogenic land subsidence a possible driver of riverine flood-hazard dynamics? A case study in Ravenna,Italy

ABSTRACT

We investigate possible changes in flood hazard over a 77-km² area around the city of Ravenna. The subsidence rate in the area, naturally a few mm year^?1, increased dramatically after World War II because of groundwater and natural gas extraction, exceeding 110?mm year^?1 and resulting in cumulative drops larger than 1.5?m. The Montone–Ronco river system flows in the southern portion of the area, which is protected against frequent flooding by levees. We performed two-dimensional simulations of inundation events associated with levee breaching by considering four different terrain configurations: current topography and a reconstruction of ground elevations before anthropogenic land subsidence, both neglecting and representing the main linear infrastructures (e.g. roads, artificial channels). Results show that flood-hazard changes due to anthropogenic land subsidence (e.g. significant changes in computed water depth and velocity) are observed over less than 10% of the study area and are definitely less important than those resulting from construction of the linear infrastructures.     

Modelling of rock alteration due to coupled heat and mass transport

 A three-dimensional computer model is presented for studying the interaction of heat and mass transport regarding the temporal and spatial evolution of sandstones. The model simulates coupled heat and reactive mass transport in porous rocks. In general, mineral solubilities in water are low. Therefore, large fluid volumes are required to flow through the rock to explain observed mineral cements in sandstones. Besides mass transport, pore fluids transport heat which modifies rock temperatures. Very high flow rates result in strong temperature modifications and, therefore, enhance diagenesis. Low flow rates often cannot account for observed cementation. The model results show the effect of advective, convective and conductive heat transport on temperature and diagenetic evolution of sandstones for two different flow systems in a simple geological environment. Received: 6 August 1996/Accepted: 18 December 1996     

The“Sand-Mud” Sedimentary Record and Its Diagenetic System in Shore-shallow Lacustrine—A Case Study of Eocene Kongdian Formation in Jiyang Depression

The sand-mud sedimentary record develops widely in the shore-shallow lacustrine, which can be a good oil and gas reservoir cap combination. It has important significance in petroleum geology. This paper takes the Kongdian Fm. of Eocene in Jiyang Depression as an example to study the formation mechanism and diagenetic system of the sand-mud sedimentary record in the shore-shallow lacustrine. The study indicated that sandstone-mudstone sedimentary strata at macroscopic level includes sand-mud duality, mudstone vein and sandstone lens in the Kongdian Fm. of Jiyang Depression, and there are some transitional clastic rocks at the microscopic level (Clastic particles, clay and carbonate cements are included in the transitional clastic rocks). The sandstone-mudstone sedimentary strata mainly formed in the material transformation of the shallow-water deltas and conjugate shock in the shore-shallow lacustrine. The thickness is mainly restricted by material source and water dynamic condition, and the sand-mud transitional clastic rocks are restricted by the dynamic mechanism and sedimentary differentiation of the lake water. The sandstone-mudstone sedimentary strata is composed of a closed diagenetic system. Early compaction-drainage and differential compaction, middle and late clay mineral transformation, structural water and organic acid emissions during the diagenetic process of mudstone influence the diagenesis of sandstone. The closed diagenetic system of sand-mud transitional clastic rocks is mainly related to the structural maturity of clastic rocks.     

川中地区上三叠统须家河组成岩层序地层学特征

充分利用薄片分析以及X-衍射等资料,结合元素俘获(ECS)测井解释所获得的岩石矿物组合特征,从层序界面对成岩特征的控制以及不同基准面旋回内的成岩作用发育规律两个方面分别对川中须家河组层序地层格架内的成岩作用特征进行探讨。结果表明,须家河组可划分为2个超长期和5个长期基准面旋回层序。须二段、须四段底部的层序界面之下碳酸盐胶结物含量普遍增加,而界面之上的砂体普遍见溶蚀现象,储层物性相对变好。须四段基准面上升半旋回时期形成的沉积物颗粒粒度较粗、泥质含量低、砂体厚度大、连通性好,在成岩过程中原生孔隙容易得到保存,再加上受到层序界面所控制的有机酸性水溶蚀作用的影响,有利于次生孔隙的产生。而基准面下降期,砂体的连通性变差、泥质夹层增多,在成岩过程中原生孔隙不易保留同时也不利于次生溶蚀孔隙的产生,因而物性最差。须二段总体也具此规律,但由于其埋藏更深,经历成岩作用更为复杂,因此并不如须四段明显。研究成果可为研究区优质储层追踪对比及预测提供依据,同时也能为成岩层序地层学的研究提供借鉴。     

内蒙古拜仁达坝银铅锌矿区成矿前围岩蚀变与元素迁移规律

为了厘清内蒙古拜仁达坝银铅锌矿床围岩蚀变特征,探索蚀变流体-岩石相互作用过程中的元素迁移规律,在野外地质工作的基础上,文章开展蚀变岩岩相学研究,发现矿区内存在多期围岩蚀变,其中成矿前蚀变规模大、强度强、范围集中、类型丰富、多阶段叠加：从早阶段硅化-绢云母化、中间阶段黏土化-绿泥石化到晚阶段碳酸盐化,且蚀变程度逐步增强。文章对矿区内不同蚀变程度的石英闪长岩和黑云斜长片麻岩的主微量元素测试和质量平衡计算表明,随着蚀变过程中原生矿物减少、蚀变矿物增加,主微量元素发生规律性迁移。结合成矿作用以高中温硫化物充填为主,矿化脉穿切各类蚀变岩、成矿元素未随蚀变增强而富集等地质事实,文章认为该期蚀变与成矿并不是同一次流体-岩石相互作用的结果,该期蚀变的体积效应可能仅有利于后期成矿物质充填的构造-围岩条件的形成。     

The Diagenesis and Diagenetic Lithofacies of Tight Reservoir of Chang4+5 Member of Yanchang Formation in Huaqing Area,Ordos Basin

Though the prospective of reserves of tight oil reservoir of Chang 4+5 member of Yanchang Formation is great in Huaqing area, Ordos Bsin, but its speed of oil exploration and development has been much restricted much by weak reservoir diagenesis research. To study the characteristics of diagenesis, diageneticfacies and physical properties of reservoir of Chang 4+5 in Huaqing area, a series of analytic techniques were used, including polarized light microscope, casting slice, scanning electron microscope, electron probe microanalysis, cathodeluminescence, micro fluorescence, X-ray diffraction, fluid inclusion, high pressure mercury, physical properties, etc. The results showed that the ferrocalcite, quartz and kaolinite cementation caused the background of low porosity and ultra low permeability reservoir of Chang 4+5 reservoir in the study area, and the diagenetic stage belonged to the “A” middle now. Chlorite film cementation and early oil accumulation effectively protected pores and limited the mechanical compaction and the cementation. The intense dissolution of feldspar could greatly improve the reservoir porosity and cause the relatively high porosity and permeability reservoir. There are mainly divided into four kinds of diagenetic facies, including chlorite cementation residual intergranular pore facies, the mechanical compaction facies, chlorite cementation and feldspathic solution facies, carbonate cementation facies. The most favorable diagenetic facies is feldspathic solution facies, which mainly distributes in the middle sandbody of the fluxoturbidite and underwater distributary channel of the main sand belt adjacent the semi-deep lake shoreline, and it is favorable to the formation of relatively high porosity and permeability reservoir, of which surface porosity is more than 6.0%, porosity is more than 16.0 %, permeability is more than 1.30×10^-3μm². Comprehensive studies have shown that the combination of sedimentation and diagenesis controls the distribution of relatively high porosity and permeability reservoir.     

西藏甲玛超大型矿床南坑厚大矽卡岩矿体的成岩-成矿-构造耦合关系

甲玛是西藏冈底斯成矿带规模大、品位富的超大型矿床,也是勘查和研究程度最高的矿床之一。其中,南坑矿段由于富含高品位的矽卡岩型铜铅锌矿石,且具大型规模,已被纳入矿区首采矿段之一,然而关于其控岩控矿机制以及其与主矿段的耦合关系却仍不明确。本次基于详细的钻孔编录和野外地质证据,判定其成矿作用与中新世的花岗闪长斑岩等中酸性斑岩体有关,结合高精度的U-Pb年代学分析,厘定含矿花岗闪长斑岩结晶年龄为（15.5±0.3）Ma,与辉钼矿成矿年龄（15.23±0.22）Ma一致。南坑矿段作为甲玛矿床多中心复合成矿作用模型的重要组成部分,其矽卡岩矿体主要产于林布宗组角岩与多底沟组大理岩之间的层间接触带,属于中新世岩浆热液活动的产物。矿体形成后,受滑覆构造及次级断裂影响,矿体发生错断或破坏。对于南坑矿段后续的勘查评价,应注意与含矿斑岩和矽卡岩的蚀变与矿化分带特征,定位致矿热液中心。