Salt insertions in sedimentary sequences: impacts on temperature and thermal maturation with depth

Due to the contrast in thermal conductivity between salt and typical sedimentary formations the presence of salt in various shapes in the sub-surface can have a significant impact on the sub-surface temperature distribution and thermal maturation of source rocks. Using a thermal indicator tomography 1-D modelling system, which deals with salt insertion, the thermal and excess maturity anomalies caused solely by the presence of a salt layer are investigated. Two cases, salt ‘plug’ and ‘lens’, illuminate the different patterns of vitrinite reflectance variation with depth that would be recorded by borehole sampling. Salt can be inserted either as a primary depositional layer or by secondary intrusion at depth. The effects of salt are more dominant on the subsalt layers because: 1 salt insertion changes the burial paths of subsalt sediments. Thus the compaction-driven fluid flow of subsalt sediments, and also basement subsidence, are altered; 2 iso-temperature lines are modified by the presence of the salt and the variation depends on the thickness of the salt layer. The model was also designed to estimate the time of salt insertion and the variation of salt thickness in an inverse sense using present day data on temperature with depth and measured thermal indicators. An investigation is given of the degree to which inverse procedures resolve parameters associated with salt insertion. The sensitivity of those parameters is also discussed.     

沾化凹陷渤南洼陷沙四段～孔店组的热史及超压演化

利用EASR%Ro模型,计算了渤南洼陷沙四段～孔店组(Es4-Ek)的古地温和古地温梯度的演变值。古地温的演变与盆地的构造演化关系密切,抬升剥蚀期地层温度下降,沉降期地层温度升高,地史过程中地温梯度的变化呈逐渐降低的趋势。采用盆地模拟技术,恢复且再现了渤南洼陷Es4-Ek地史期的超压演化过程。此过程与该区构造演化和有机质生烃增压作用紧密相关,沉积和剥蚀速率及地层地史期的孔渗性决定了早期超压幅度的高低,而后期构造运动的改造及有机质的生烃作用,决定了现今压力系数的大小。压力在漫长的发展演化过程中,经历了超压积累～破裂泄压～超压再积累～再破裂泄压的反复过程,说明盆地的压力场是一个动态发展的过程,其间伴随着高压流体的幕式排放。     

The influence of faults and intraplate stresses on the overpressure evolution of the Halten Terrace, mid-Norwegian margin

The Halten Terrace is a structural element of the Meso-Cenozoic mid-Norwegian margin. The pore fluid pressure distribution in the faulted Jurassic formations on the Halten Terrace is characterized by significant lateral variations. In general, the fluid overpressure increases stepwise across faults from east to west, from zero (hydrostatic fluid pressure) to about 30 MPa. Fault-bounded pressure cells can therefore best explain the fluid pressure distribution. The results of analyses of log-derived porosities indicate that the high overpressure in the westernmost pressure cell was built up recently. However, despite the high sedimentation rates during Plio-Pleistocene, the high overpressure cannot be explained by local mechanical compaction. Alternative explanations for the high overpressure proposed by other authors are based on pore fluid volume increase (e.g. hydrocarbon generation). We propose that the high overpressure is caused by fluid flow from the deep Rås Basin to the western part of the Halten Terrace, through fractures in the Mesozoic, deep seated Klakk Fault Complex. Opening of fractures in this fault zone by seismic and static mechanisms is possible in the present-day intraplate stress field, which is characterized by a NW–SE oriented maximum horizontal stress direction. During Miocene, the maximum horizontal stress was E–W oriented, which implies a stress rotation during Pliocene. The E–W orientation of the maximum horizontal stress has impeded the initiation and opening of fractures in the N–S striking Klakk Fault Complex during Miocene. Fluid flow from the Rås Basin through faults of the Klakk Fault Complex can therefore have occured since Pliocene. Thus, the rotation of the intraplate stress directions can explain why the build-up of overpressure on the western part of the Halten Terrace occured recently, as indicated by the results of porosity analyses. Understanding the overpressure evolution of the Halten Terrace is important for exploration in that area, as hydrocarbons have been found in the hydrostatic pressure cells, whereas they are absent in the high overpressure cells.     

2019年3月柴达木盆地茫崖5.0级地震构造与油田井损关系分析

地震引起的油气勘探开发过程中的钻井破坏日益引发关注,研究地震构造与钻井破坏之间的关系对油田安全生产非常重要。2019年3月28日青海省茫崖地区发生一系列地震,最大震级达5.0级,震中位于柴西狮子沟构造,并且在地震期间狮子沟地区钻井发生破坏。结合高精度地震勘探数据与钻井资料,本文刻画了狮子沟地区的地震构造与井损点分布特征,进一步探讨钻井破坏的原因。研究表明狮子沟构造是本次地震的发震构造,由盐上滑脱构造与盐下基底卷入的正花状构造组成,两者夹有厚度不均匀的盐岩体。在地震中被破坏的钻井集中分布于狮子沟背斜北东翼,靠近盐岩体厚度最大的区域。钻井井损点大致位于盐岩体顶面的连面且平行于地层层面。震源机制解指示存在倾向南南东、倾角较陡、以逆倾滑分量为主、兼有左行走滑分量与倾向北东、倾角较缓、兼有逆倾滑分量与右行走滑分量的两节面,分别对应盐下基底断裂的分支断裂与盐上逆冲滑脱断裂。考虑到震源位置的不确定性,盐下分支断裂或盐上逆冲滑脱断裂可能是本次地震的发震断裂,其中后者具有更大的可能性。钻井破坏的原因是同震断层活动造成的沿不稳定盐层顶面发生顺层剪切。因此,本文报道了盐构造环境下地震造成钻井破坏的实例。     

Quantitative models of very high fluid pressure: the possible role of lateral stresses

Because of the occurrence of very large observed overpressure in a well located in SE Asia, numerical modelling has been undertaken to evaluate evolution of the sediments. The intensity of the excess pressure, close to lithostatic pressure, and the likely relation to induced, open-fracture anomalies, as well as evidence of large fluid transfers, all lead to the suggestion that the tectonic regime is related to the generation of high excess pressure. To verify this hypothesis, a 2D fluid-flow/compaction model (GEOPETTI) was used to test whether high excess pressure could be obtained without considering the effect of lateral stresses. While high excess pressures are possible, even if undercompaction is the only process considered, the distribution of fluid pressure with depth does not correspond to that observed, and the migration of fluids cannot be reproduced because of the extremely low permeability of the sediments. Accordingly, the model has been modified so that the effect of lateral stresses can be investigated through: (1) the value of the fracturing coefficient which controls the maximum overpressure that it is possible to generate; (2) the sensitivity of the system to a possible compressive event, which could squeeze the sediments laterally so that the rate of fluid expulsion would be greater than if the fluids were driven only by the mechanical load of sediments. Finally, the role of faulting or fracturing is discussed as a possible mechanism responsible for the upward transfer of fluid which can lead to an increase of excess pressure at depths shallower than the depth where excess pressure was first generated, a mechanism also leading to high excess pressure. Moreover, this mechanism allows for a good reproduction of observed excess pressure distributions.     

膏盐脱水在盐底辟发育过程中的作用分析-以东营凹陷为例

基于国内外已经取得的盐构造研究成果, 根据东营凹陷盐构造的发育特征, 指出流体在盐构造发育过程的重要作用。东营凹陷沙四段含有大量膏盐和含膏地层, 根据岩心、测井和地震等资料分析了东营凹陷盐构造特征。由于膏盐脱水作用会导致地层内部产生异常高压, 而异常高压可以作为动力迫使流体向上流动继而在上覆地层产生水压力裂缝, 流体上涌过程中可以带动盐类物质向上运动, 因此认为膏盐脱水对盐构造形成发育有重要作用。基于膏盐脱水和超压流体作用, 建立了东营凹陷沙四段盐底辟构造发展史模型, 分析了东营凹陷盐构造在流体作用下形成发育过程, 结果表明膏盐脱水在盐构造发育初期和中期具有重要作用。      

Development of Diapirs and Accumulation of Natural Gases in Yinggehai Basin

Ｏｖｅｒｐｒｅｓｓｕｒｅｈａｓｂｅｅｎｆｏｕｎｄｉｎａｂｏｕｔ 180ｓｅｄｉｍｅｎｔａｒｙｂａｓｉｎｓ(ＬａｗａｎｄＳｐｅｎｃｅｒ,1998;Ｈｕｎｔ,1990 ) .Ｔｈｅｍｅｃｈａｎｉｓｍｓｆｏｒｔｈｅｏｖｅｒｐｒｅｓｓｕｒｅｄｇｅｎｅｒａｔｉｏｎａｎｄｔｈｅｆｌｕｉｄｆｌｏｗａｃｔｉｖｉｔｉｅｓｉｎｏｖｅｒｐｒｅｓ ｓｕｒｅｄｂａｓｉｎｓｈａｖｅｂｅｅｎｔｈｅｓｕｂｊｅｃｔｓｏｆａｎｕｍｂｅｒｏｆｓｔｕｄｉｅｓ (Ｈｕｎｔ,1996 ;Ｏｒｔｏｌｅｖａ ,1994) .Ｐｒｏｂａｂｌｙ ,ｔｈｅｍｏｓｔｉｍｐｏｒｔａｎｔａｓｐ…     

塔里木盆地库车前陆褶皱带中段盐相关构造特征与油气聚集

塔里木盆地北部库车前陆褶皱带古新统一始新统发育盐岩层系，将库车前陆褶皱带构造变形和圈闭样式分为三层，即盐上构造、盐层(盐间)构造和盐下构造。盐上构造包括盐上背斜、盐上逆冲断层及断层相关褶皱、盐上背冲断块构造、强制褶皱、盐上逆冲断层遮挡构造和盐推覆构造等；盐层(盐间)构造主要包括盐枕构造、盐间断褶构造、盐焊接构造和外来盐席等；盐下构造主要有背冲断块构造、断层相关褶皱、叠瓦冲断带和双重构造等。库车前陆褶皱带盐构造的形成可能受挤压作用、重力滑动和重力扩展作用多重控制。笔者等讨论了盐相关构造油气成藏条件和模式，认为库车前陆褶皱带盐岩层变形与丰富的圈闭构造形成密切相关，烃源岩主要位于盐下，盐岩层作为优质盖层构成石油和天然气藏最优越的遮挡条件，断裂对盐下、盐间和盐上油气成藏都起重要控制作用，但盐下是最有利的油气聚集场所。     

库车冲断带秋里塔格构造带东段构造样式与构造演化

秋里塔格构造带位于库车褶皱冲断前缘,其东段包括东秋里塔格背斜和库车塔吾背斜。野外调查和地震剖面解释表明:秋里塔格构造带东段盐下发育断层转折褶皱; 盐上东秋里塔格背斜为滑脱箱状背斜,库车塔吾背斜核部为南倾逆冲断层所破坏。演化剖面显示秋里塔格构造带东段在侏罗纪断陷期发育了正断裂,其后为平静期,直到库车晚期后逆冲断层和褶皱快速发育,背斜最终形成。膏盐岩及古构造对构造变形具有重要影响,一方面作为滑脱层,分割了盐下层与盐上层,导致二者形成不同的构造样式; 另一方面塑性流动充填于背斜核部。由于膏盐岩的厚度差异,东秋里塔格背斜盐上发育褶皱,而库车塔吾背斜核部被逆冲断层破坏,膏盐层厚度还影响了膏盐层上下构造高点的相对位置。盐下构造的发育受侏罗纪古构造控制,进而影响了盐上构造的发育。     

Fluid inclusion evidence for deep burial of the Tertiary accretionary wedge of the Carpathians

Hydrothermal quartz from mineralized joints of the Carpathian accretionary wedge contains immiscible aqueous, oil‐condensate, methane and carbon dioxide‐rich fluid inclusions. Distribution patterns of the inclusion trapping PT parameters point to a crack‐seal mechanism during upward and lateral migration of hot methane‐rich fluids from overpressured sediments at the base of the accretionary wedge. A simple equation is proposed to calculate depths from densities and trapping pressures of the buoyant inclusion fluids. In the Carpathian accretionary wedge, the paleofluid pressures of 52–306 MPa correspond to a 5‐ to 11‐km‐thick overburden. Prior to exhumation, thickness of the wedge must have attained 10–25 km, of which only c. 50% was preserved until recently. Anomalously high methane densities (up to 0.43 g cm^?3) recorded in the lowermost nappe sheets are provisionally interpreted as a result of supralithostatic overpressure due to thermal cracking of oil and kerogen to methane and pyrobitumen at temperatures above 200 °C.     

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.     

明格布拉克油田超压流体封存箱特征

费尔干纳盆地明格布拉克油田属于超深层油气藏,油气层普遍存在超压异常,压力系数可达2.0以上,地层发育盐岩、膏盐层,低孔隙储层中裂缝发育,油田的这些特征与流体封存箱的形成和存在有很大关系。通过研究认为,不均衡压实及构造挤压环境是新近系地层形成超压的宏观成因机制,而发育岩盐层且累积厚度达到了200 m以上是现今油田保存超压的重要条件;古近系及新近系下部地层中存在两个超压流体封存箱,上部封存箱的地层压力系数略大于下部封存箱,上、下超压封存箱内流体性质存在较大的差异,是两个相对独立的成藏系统。上部封存箱又被2个岩盐封隔层分隔为3个次一级的、呈阶梯式的超压箱。封存箱内的超压、微裂缝以及岩盐层是钻探过程中发生井涌、井漏及卡钻等钻井事故的主要原因;除已发现的下部封存箱和上Ⅲ次级封存箱油气藏外,上Ⅱ次级封存箱的底部具有一定的勘探潜力;超深层的高密度原油与超压流体封存箱的存在有关,封存箱内的超高压使油气藏储层裂缝处于开启状态,有利于形成高产油气流,但同时也易于早期见水。     

Consequences of Water Level Drops for Soft Sediment Deformation and Vertical Fluid Leakage

Both water level drops and erosion have previously been suggested as causes of fluid overpressures in the subsurface. Quantification of the relevance of these processes to supra-lithostatic fluid pressure formation with a wide selection of input parameters is lacking, and thus desired. The magnitudes and drop times that are required for water level drops to result in supra-lithostatic pore pressures in a variety of situations are calculated. Situations with pore fluids consisting of water, water with dissolved methane, water with a gas hydrate layer and dissolved methane in the underlying sediments, and water with dissolved methane, a gas hydrate layer, and free gas accumulation below the hydrate layer are separately addressed. The overpressure formation from reservoir gas expansion is also simulated. The simulation results demonstrate that high fluid overpressures can develop in a rock as a response to a water level drop without the presence of gas, provided that the rock has a sufficiently low compressibility. The contribution to fluid overpressuring is however dramatically increased if the pore water is saturated with methane prior to the water level drop, and is further amplified by the presence of gas hydrates and free gas accumulations beneath such hydrates. Gas expansion in reservoirs should be expected to significantly increase the fluid overpressures in shallow, sealed pressure compartments that experience erosion or water level drops, even if the water level drop duration exceeds one million years. Enough relationships between the calculated overpressure formation and the main controlling factors are provided in order to enable readers to make inferences about a variety of geological settings. Analyses of simulation results prompt us to suggest that pockmarks are likely to be triggered by gas expansion in vertical fluid migration pathways, that the giant craters at the seabed west of Albatross South in the Barents Sea result from hydrate dissociation, and that overpressure build-up due to gas expansion has contributed to reservoir overpressuring in many eroded basins, including the Hammerfest Basin in the Barents Sea.     

Controls on the deep thermal field: implications from 3-D numerical simulations for the geothermal research site Groß Schönebeck

The deep thermal field in sedimentary basins can be affected by convection, conduction or both resulting from the structural inventory, physical properties of geological layers and physical processes taking place therein. For geothermal energy extraction, the controlling factors of the deep thermal field need to be understood to delineate favorable drill sites and exploitation compartments. We use geologically based 3-D finite element simulations to figure out the geologic controls on the thermal field of the geothermal research site Groß Schönebeck located in the E part of the North German Basin. Its target reservoir consists of Permian Rotliegend clastics that compose the lower part of a succession of Late Carboniferous to Cenozoic sediments, subdivided into several aquifers and aquicludes. The sedimentary succession includes a layer of mobilized Upper Permian Zechstein salt which plays a special role for the thermal field due to its high thermal conductivity. Furthermore, the salt is impermeable and due to its rheology decouples the fault systems in the suprasalt units from subsalt layers. Conductive and coupled fluid and heat transport simulations are carried out to assess the relative impact of different heat transfer mechanisms on the temperature distribution. The measured temperatures in 7 wells are used for model validation and show a better fit with models considering fluid and heat transport than with a purely conductive model. Our results suggest that advective and convective heat transport are important heat transfer processes in the suprasalt sediments. In contrast, thermal conduction mainly controls the subsalt layers. With a third simulation, we investigate the influence of a major permeable and of three impermeable faults dissecting the subsalt target reservoir and compare the results to the coupled model where no faults are integrated. The permeable fault may have a local, strong impact on the thermal, pressure and velocity fields whereas the impermeable faults only cause deviations of the pressure field.     

评述异常压力研究中的石油地质学新思想

在对异常压力的认识不断深化的过程中,凝结出许多新的概念和思想,为现代石油地质学理论注入了新的内容。关于超压生成与有机质成熟-生烃的关系虽有争议,但大多数主张超压对有机质成熟和生烃起抑制作用;在超压的背景下,生烃、排烃以及烃类的运移和聚集常呈现出幕式的特征;压力驱动是流体活动和油气运移的重要动力;动态运移通道是油气运移的新型通道;通常压力过渡带是油气聚集的有利场所;在超压的含油气盆地中,可能发现的非传统油气聚集有异常压力的气饱和封存箱、水力破裂-泥岩裂缝油气藏、烃水倒置的油气藏等。异常压力的储层具有相对独立性。     

Evaporites,brines and base metals: Low‐temperature ore emplacement controlled by evaporite diagenesis

Salt beds and salt allochthons are transient features in most sedimentary basins, which through their dissolution can carry, focus and fix base metals. The mineralisation can be subsalt, intrasalt or suprasalt, and the salt body or its breccia can be bedded or halokinetic. In all these evaporite‐associated low‐temperature diagenetic ore deposits there are four common factors that can be used to recognise suitably prepared ground for mineralisation: (i) a dissolving evaporite bed acts either as a supplier of chloride‐rich basinal brines capable of leaching metals, or as a supplier of sulfur and organics that can fix metals; (ii) where the dissolving bed is acting as a supplier of chloride‐rich brines, there is a suitable nearby source of metals that can be leached by these basinal brines (redbeds, thick shales, volcaniclastics, basalts); (iii) there is a stable redox interface where these metalliferous chloride‐rich waters mix with anoxic waters within a pore‐fluid environment that is rich in organics and sulfate/sulfide/H₂S; and (iv) there is a salt‐induced focusing mechanism that allows for a stable, long‐term maintenance of the redox front, e.g. the underbelly of the salt bed or allochthon (subsalt deposits), dissolution or halokinetically maintained fault activity in the overburden (suprasalt deposits), or a stratabound intrabed evaporite dissolution front (intrasalt deposits). The diagenetic evaporite ‐ base‐metal association includes world‐class Cu deposits, such as the Kupferschiefer‐style Lubin deposits of Poland and the large accumulations in the Dzhezkazgan region of Kazakhstan. The Lubin deposits are subsalt and occur where long‐term dissolution of salt, in conjunction with upwelling metalliferous basin brines, created a stable redox front, now indicated by the facies of the Rote Faule. The Dzhezkazgan deposits (as well as smaller scale Lisbon Valley style deposits) are suprasalt halokinetic features and formed where a dissolving halite‐dominated salt dome maintained a structural focus to a regional redox interface. Halokinesis and dissolution of the salt bed also drove the subsalt circulation system whereby metalliferous saline brines convectively leached underlying sediments. In both scenarios, the resulting redox‐precipitated sulfides are zoned and arranged in the order Cu, Pb, Zn as one moves away from the zone of salt‐solution supplied brines. This redox zonation can be used as a regional pointer to both mineralisation and, more academically, to the position of a former salt bed. In the fault‐fed suprasalt accumulations the feeder faults were typically created and maintained by the jiggling of brittle overburden blocks atop a moving and dissolving salt unit. A similar mechanism localises many of the caprock replacement haloes seen in the diapiric provinces of the Gulf of Mexico and Northern Africa. Evaporite‐associated Pb–Zn deposits, like Cu deposits, are focused by brine flows associated with both bedded and halokinetic salt units or their residues. Stratabound deposits, such as Gays River and Cadjebut, have formed immediately adjacent to or within the bedded salt body, with the bedded sulfate acting as a sulfur source. In allochthon/diapir deposits the Pb–Zn mineralisation can occur both within a caprock or adjacent to the salt structure as replacements of peridiapiric organic‐rich pyritic sediments. In the latter case the conditions of bottom anoxia that allowed the preservation of pyrite were created by the presence of brine springs and seeps fed from the dissolution of nearby salt sheets and diapirs. The deposits in the peridiapiric group tend to be widespread, but individual deposits tend to be relatively small and many are subeconomic. However, their occurrence indicates an active metal‐cycling mechanism in the basin. Given the right association of salt allochthon, tectonics, source substrate and brine ponding, the system can form much less common but world‐class deposits where base‐metal sulfides replaced pyritic laminites at burial depths ranging from centimetres to kilometres. This set of diagenetic brine‐focusing mechanisms are active today beneath the floor of the Atlantis II Deep and are thought to have their ancient counterparts in some Proterozoic sedex deposits. The position of the allochthon, its lateral continuity, and the type of sediment it overlies controls the size of the accumulation and whether it is Cu or Pb–Zn dominated.     

砂岩透镜体油气藏成因机理与模式

泥岩层的幕式压实/压裂现象和砂岩透镜体中沸腾包裹体的发现,证明了该类圈闭成藏过程中超压流体幕式充注机制的存在。综合考虑油气运聚的动力与作用方式、输导格架类型与流体流动样式、成藏特征、运聚机理和成藏模式,将砂岩透镜体动力学成因类型划分为毛细管力-超压联控型和超压单控型。对砂岩透镜体中的流体排放机制进行了探讨,并认为处于强超压状态的砂岩透镜体油气藏可能存在侧向和垂向两种流体排放模式。     

东濮凹陷文留地区深层强超压环境下有机质热演化

东濮凹陷文留地区的地层普遍发育超压甚至强超压系统.超压与地层有机质热演化反应过程存在复杂的相关性.深层盐下、盐间地层有机质的热演化受强超压的影响,不同热演化反应过程不同程度地受到抑制作用:镜质体反射率演化正常;烃类裂解以及烃类结构演化在深层强超压作用下受到抑制作用.有机质热演化过程中的超压抑制为深层源岩成烃提供了更为有利的条件,是文留地区深层天然气成藏的主要因素.     

莺歌海盆地超压流体活动与断裂系统的相互关系

莺歌海盆地内超压流体活动十分强烈，主要活动形式有侧向对流型和垂向对流型，将超压流体的演化与区域构造演化结合起来，对断裂与超压流体的成因关系提出了新见解，揭示出断裂对超压流体的输导及超压流体对断裂的开启的相互作用。张裂隙作为超压流体活动的诱导，超压的幕式突破就主要起因于上覆负载层中的断裂、破碎带，发生压力释放；而普遍发生的幕式流体释放又进一步开启垂直裂隙，造成上下地层间的连通，从而作为超压突破的诱因。     

东营凹陷沙四段盐湖的深水成因模式

东营凹陷下第三系沙四段广泛发育的蒸发岩类与暗色泥、页岩和深水浊积砂体呈现明显韵律层,为厚度达千米的盐湖沉积。通过分析了该地区蒸发岩地层的沉积特征和沉积条件,认为东营凹陷沙四段蒸发岩类的物质基础是深层卤水 深部古老地层中的盐类物质是其盐源 凹陷中北部的同沉积深大断裂是沟通凹陷与地壳深部盐类物质的通道。在此基础上提出东营凹陷沙四段盐湖的深水成因模式,可与东非裂谷基伍湖和东濮凹陷下第三系深水成因盐湖对比。