THE THERMAL GRADIENT HISTORY OF THE THRACE BASIN, NW TURKEY: CORRELATION WITH BASIN EVOLUTION PROCESSES

Thermal maturity modelling is widely used in basin modelling to help assess the exploration risk. Of the calibration algorithms available, the Easy%Ro model has gained wide acceptance. In this study, thermal gradients at 70 wells in the Thrace Basin, NW Turkey, were calibrated against vitrinite reflectance (%Ro) using the Easy%Ro model combined with an inverse scheme. The mean squared residual (MSR) was used as a quantitative measure of mismatch between the modelled and measured %Ro. A 90% confidence interval was constructed on the mean of squared residuals to assess uncertainty. The best thermal gradient (i.e. minimum MSR) was obtained from the MSR curve for each well, and an average palaeo‐thermal gradient map of the Thrace Basin was therefore created. Calculated thermal gradients were compared to the results of previous studies. A comparison of modelled palaeo‐thermal gradients with those measured at the present day showed that the thermal regime of the Thrace Basin has not changed significantly during the basin's history. The geological and thermal characteristics of the Thrace Basin were compared and the thermal anomalies were evaluated as a function of basin evolution processes. The basin's thermal regime was controlled by: (1) basement edge effects; (2) crustal thickness and basement heat flows; (3) thermal conductivity variations within the stratigraphic column; (4) transient heat flow effects; and (5) the influence of tectonic features. The impact of these factors on variations in the thermal gradients is discussed in detail. Basement edge effects are most marked on the steep northern margin of the basin where heat is preferentially retained in highly conductive basement rocks rather than being transferred into less conductive sedimentary rocks. Thus, heat is significantly focused onto the northern edge of the basement, resulting in a thermal anomaly along the northern basin margin. The margins of the basin, with relatively thick upper crust, have relatively higher thermal gradients compared to the central areas. This is due to radiogenic heat production in the upper crust. Thus, thermal gradients increase above highs and at the margins where thicker upper crust is present. A heat flow map of the Thrace Basin, constructed using a basin‐scale crustal thickness map and a basement heat‐flow algorithm, is presented and demonstrates the heat generation potential of the upper crust. The Eocene Ceylan Formation, which has relatively low thermal conductivity, significantly reduces the thermal gradients by blocking heat transferred from the basement. Areas of high sedimentation rate are associated with low thermal gradients due to the transient heat flow effects of young, thick and “thermally immature” sediments as a function of the heat capacities of these deposits. A direct relationship between thermal gradients and major structural trends could not be established because of a number of factors including the inactivity of the subsurface Miocene fault systems, which did not allow the flow of high temperature fluids through to shallow depths; also, the steady burial and sedimentation rates since the Early Eocene have maintained the pressure system in equilibrium.     

A RAPID METHOD OF QUANTIFYING THE RESOLUTION LIMITS OF HEAT-FLOW ESTIMATES IN BASIN MODELS

Deterministic forward models are commonly used to quantify the processes accompanying basin evolution. Here, we describe a workflow for the rapid calibration of palaeo heat‐flow behaviour. The method determines the heat‐flow history which best matches the observed data, such as vitrinite reflectance, which is used to indicate the thermal maturity of a sedimentary rock. A limiting factor in determining the heat‐flow history is the ability of the algorithm used in the software for the maturity calculation to resolve information inherent in the measured data. Thermal maturation is controlled by the temperature gradient in the basin over time and is therefore greatly affected by maximum burial depth. Calibration, i.e. finding the thermal history model which best fits the observed data (e.g. vitrinite reflectance), can be a time‐consuming exercise. To shorten this process, a simple pseudo‐inverse model is used to convert the complex thermal behaviour obtained from a basin simulator into more simple behaviour, using a relatively simple equation. By comparing the calculated “simple” maturation trend with the observed data points using the suggested workflow, it becomes relatively straightforward to evaluate the range within which a best‐fit model will be found. Reverse mapping from the simple model to the complex behaviour results in precise values for the heat‐flow which can then be applied to the basin model. The goodness‐of‐fit between the modelled and observed data can be represented by the Mean Squared Residual (MSR) during the calibration process. This parameter shows the mean squared difference between all measured data and the respective predicted maturities. A minimum MSR value indicates the “best fit”. Case studies are presented of two wells in the Horn Graben, Danish North Sea. In both wells calibrating the basin model using a constant heat‐flow over time is not justified, and a more complex thermal history must be considered. The pseudo‐inverse method was therefore applied iteratively to investigate more complex heat‐flow histories. Neither in the observed maturity data nor in the recorded stratigraphy was there evidence for erosion which would have influenced the present‐day thermal maturity pattern, and heat‐flow and time were therefore the only variables investigated. The aim was to determine the simplest “best‐fit” heat‐flow history which could be resolved at the maximum resolution given by the measured maturity data. The conclusion was that basin models in which the predicted maturity of sedimentary rocks is calibrated solely against observed vitrinite reflectance data cannot provide information on the timing of anomalies in the heat‐flow history. The pseudo inverse method, however, allowed the simplest heat‐flow history that best fits the observed data to be found.     

GEOHISTORY, THERMAL HISTORY AND HYDROCARBON GENERATION HISTORY OF NAVARIN BASIN COST NO. 1 WELL, BERING SEA, ALASKA

Using a one-dimensional model, we numerically simulate with time the geological processes of sedimentary deposition, compaction, fluid flow, heat flow and hydrocarbon generation. Input well data, in the form of present-day formation thicknesses, porosity with depth, thermal gradient, vitrinite reflectance with depth, and fluid overpressure with depth constrain the dynamical model. We present model results for the Navarin Basin COST No. 1 well, including reconstructions of burial history, fluid flow history, thermal history and hydrocarbon generation history.
We also demonstrate how important geophysical variables (such as permeability, porosity, fluid pressure, fluid-flow rate, and thermal maturity indicators) vary with depth and time. Comparison of the model results with observed data illustrates and emphasizes the capabilities of the modelling procedure.
The significance of the dynamical model is that it permits a quantitative assessment to be made of (i) the timing and depth locations of the generation and migration of hydrocarbon in a basin, relative to the formation of structural and stratigraphic traps: (ii) the timing of the production of overpressuring and fracturing within a basin: and (iii) the effect of cementation and dissolution on the retention of hydrocarbons in a trap. The model also enables an assessment to be made of the most likely prospective areas for hydrocarbon accumulation in a basin.     

野外露头的盆地模拟研究与地下烃源岩有机质成熟度的预测

本文在国内首次模拟了野外露头的埋藏史和地热史,并通过人工改变埋藏轨迹,预测了盆地内中侏罗统地下烃源岩的有机质成熟度.西宁盆地现今出露的中侏罗统烃源岩的镜质体反射率为0.59%,刚进人生油门限.模拟结果表明:地下同层位、同深度烃源岩的镜质体反射率为0.82%,达到了大量生油的成熟阶段.     

鄂尔多斯盆地热演化史与油气关系的研究

通过镜质体反射率、包裹体测温、磷灰石裂变径迹等多种古地温研究方法,结合盆地构造演化史,恢复了鄂尔多斯盆地热演化史,古生代到中生代早期地温梯度都较低(2.2～3.0℃/100m),中生代晚期地温梯度升高到3.3～4.5℃/100m,新生代以来逐渐降低到2.8℃/100m.古生代和中生代早期,地温锑度低,气源岩热演化程度低.有利于有机质的保存.中生代晚期地温梯度高,是古生界碳酸盐岩及煤系地层的主要生气期和运移期.新生代以来地温逐渐降低,生气作用减弱或停止.鄂尔多斯盆地内部缺乏断裂,生气高峰期较晚,有利于大气田的保存,鄂尔多斯盆地中央古隆起由于孔隙发育又临近主要生气区,应是首选的勘探目标.     

EASY%Ro模型在我国西部中生代盆地热史研究中的应用

有机质的成熟度主要是由其经历的热历史所决定的,基于二者之间的对应关系,不仅可以通过热史对成熟度进行研究和模拟,而且科研生产中更经常,更需要做的一作是根据有机质的成熟度来反演其所经历的热史。     

EASY%R_0模型在我国西部中生代盆地热史研究中的应用

镜质组反射率（Ｒ０）的大小取决于有机质受热温度和受热时间,因此,根据Ｒ０可以重构有机质热历史。在勘探程度较低时,恢复热史的常规模型和方法存在较大的缺陷,相比之下,ＥＡＳＹ％Ｒ０化学动力学模型更能真实地再现有机质所经历的热史,尤其是在Ｒ０值大于０．９％的中、高成熟演化阶段应用效果更佳。鉴于此,利用ＥＡＳＹ％Ｒ０模型,同时结合镜质组反射率资料,对塔里木盆地库车坳陷依南２井、雅布赖盆地雅参１井和酒西盆地医１０１井进行了热史模拟。研究结果表明,自中生代以来,库车坳陷古地热梯度总体上呈降低趋势,相对较明显的降温过程与晚第三纪快速埋藏过程相对应。雅参１井和窿１０１井的古地热梯度偏低,并且变化不大,不利于有机质生烃。镜质组反射率测定值的差异性可能是导致依南２井热史模拟计算的古地热梯度高于前人研究结果的主要原因。图４表４参５（魏志彬摘）     

RELATIONS BETWEEN DEPTH OF BURIAL, VITRINITE REFLECTANCE AND GEOTHERMAL GRADIENT

In wells where the drilled sequence is now at its maximum temperature, relations between depth and vitrinite reflectance show three segments: an upper segment with a linear gradient from 0.2–0.25% Ro at the surface to 0.6–0.7% Ro; a middle segment in which reflectance increases rapidly to c. 1.0% R; and a lower segment in which the gradient is again linear but reflectance increases more rapidly than in the upper segment. With a linear scale for depth, the inflection represented by the short middle segment tends to be obscured by the adoption by some authors of a log scale for reflectance.
The depth to the inflection systematically increases with decrease in geothermal gradient, allowing the development of a general diagram relating depth, reflectance and geothermal gradient. In wells where erosion is probable either at the present-day surface or at an unconformity, the general diagram can be used to estimate former maximum depths of burial and paleogeothermal gradients. These estimates, together with the presence of the inflection in the depth/reflectance relation, should be part of the input into modelling of the thermal history of sedimentary basins when reflectance is used in the model. The inflection is the result of the changing chemistry of vitrinite during oil generation, and the contrast between the depth/reflectance gradients above and below the inflection comparably reflects the contrast in vitrinite chemistry.     

中国大陆地区沉积盆地的热状况、热历史和生烃史

1. Introduction The thermal regime or thermal background is an important tool for revealing the geodynamic processes of the continental lithosphere and establishing the onset of the generation of hydrocarbons from source rocks in sedimentary basins (Chapm…     

流体包裹体在盆地热史研究中的应用与问题讨论

矿物流体包裹体中保留了大量盆地形成过程中成矿流体的温度、压力等信息,因而在盆地的热史研究中得到了广泛的应用。介绍了流体包裹体在盆地古地温及古地温梯度中应用的基本情况,分析了该方法的优点及存在的一些问题,并指出了多种古温标法相互对比、相互验证与相互补充才是盆地热史研究的有效方法。     

BURIAL AND THERMAL HISTORY MODELLING OF THE MANNAR BASIN,OFFSHORE SRI LANKA

The Mannar Basin is a Late Jurassic – Neogene rift basin located in the Gulf of Mannar between India and Sri Lanka which developed during the break‐up of Gondwana. Water depths in the Gulf of Mannar are up to about 3000 m. The stratigraphy is about 4 km thick in the north of the Mannar Basin and more than 6 km thick in the south. The occurrence of an active petroleum system in the basin was confirmed in 2011 by two natural gas discoveries following the drilling of the Dorado and Barracuda wells, located in the Sri Lankan part of the Gulf. However potential hydrocarbon source rocks have not been recorded by any of the wells so far drilled, and the petroleum system is poorly known. In this study, basin modelling techniques and measured vitrinite reflectance data were used to reconstruct the thermal and burial history of the northern part of the Mannar Basin along a 2D profile. Bottom‐hole temperature measurements indicate that the present‐day geothermal gradient in the northern Mannar Basin is around 24.4 ^oC/km. Optimised present‐day heat flows in the northern part of the Mannar Basin are 30–40 mW/m². The heat flow histories at the Pearl‐1 and Dorado‐North well locations were modelled using SIGMA‐2D software, assuming similar patterns of heat flow history. Maximum heat flows at the end of rifting (Maastrichtian) were estimated to be about 68–71 mW/m². Maturity modelling places the Jurassic and/or Lower Cretaceous interval in the oil and gas generation windows, and source rocks of this age therefore probably generated the thermogenic gas found at the Dorado and Barracuda wells. If the source rocks are organic‐rich and oil‐ and gas‐prone, they may have generated economic volumes of hydrocarbons.     

Ro反演的盆地热史恢复方法与相关问题

同一盆地不同深度的镜质体反射率(R_o)是盆地所受热流密度变化的反映。因此,可通过建立盆地的古热流、古地温及镜质体反射率模型来反映盆地演化历史。但是,R_o在多旋回盆地中存在多解性及不可逆性。所以,在用R_o进行盆地反演时,应从原始盆地恢复入手,最大限度地挖掘可靠的R_o资料;为了克服R_o的不可逆性及可掩盖性,可将lgR_o-H剖面进行分段综合解释,对于被不整合分隔的沉积层,分段求取平均R_o值作为该段的R_o值,对于突变的lgR_o-H曲线,则应注意局部火山活动的影响,剔除异常值;另外,盆缘露头及浅埋区的R_o资料则主要用于说明盆地演化早期的古地温场特征。     

IMPACT OF MAGMATISM ON PETROLEUM SYSTEMS IN THE SVERDRUP BASIN, CANADIAN ARCTIC ISLANDS, NUNAVUT: A NUMERICAL MODELLING STUDY

Numerical modelling is used to investigate for the first time the interactions between a petroleum system and sill intrusion in the NE Sverdrup Basin, Canadian Arctic Archipelago. Although hydrocarbonexploration has been successful in the western Sverdrup Basin, the results in the NE part of thebasin have been disappointing, despite the presence of suitable Mesozoic source rocks, migrationpaths and structural/stratigraphic traps, many involving evaporites. This was explained by (i) theformation of structural traps during basin inversion in the Eocene, after the main phase ofhydrocarbon generation, and/or (ii) the presence of evaporite diapirs locally modifying the geothermalgradient, leading to thermal overmaturity of hydrocarbons. This study is the first attempt at modellingthe intrusion of Cretaceous sills in the east‐central Sverdrup Basin, and to investigate how theymay have affected the petroleum system. A one‐dimensional numerical model, constructed using PetroMod9.0®, investigates the effectsof rifting and magmatic events on the thermal history and on petroleum generation at the DepotPoint L‐24 well, eastern Axel Heiberg Island (79°23′40″N, 85°44′22″W). The thermal history isconstrained by vitrinite reflectance and fission‐track data, and by the tectonic history. The simulationidentifies the time intervals during which hydrocarbons were generated, and illustrates the interplaybetween hydrocarbon production and igneous activity at the time of sill intrusion during the EarlyCretaceous. The comparison of the petroleum and magmatic systems in the context of previouslyproposed models of basin evolution and renewed tectonism was an essential step in the interpretationof the results from the Depot Point L‐24 well. The model results show that an episode of minor renewed rifting and widespread sill intrusionin the Early Cretaceous occurred after hydrocarbon generation ceased at about 220 Ma in theHare Fiord and Van Hauen Formations. We conclude that the generation potential of these deeperformations in the eastern Sverdrup Basin was not likely to have been affected by the intrusion ofmafic sills during the Early Cretaceous. However, the model suggests that in shallower sourcerocks such as the Blaa Mountain Formation, rapid generation of natural gas occurred at 125 Ma, contemporaneous with tectonic rejuvenation and sill intrusion in the east‐central Sverdrup Basin.A sensitivity study shows that the emplacement of sills increased the hydrocarbon generation ratesin the Blaa Mountain Formation, and facilitated the production of gas rather than oil.     

油气系统动态数值模拟研究（一）——技术思路与软件流程

油气系统是最适于进行盆地模拟评价的油气地质单元，盆地模拟的特点体现了油气系统的认识论。油气系统分析模拟的内容应包括①静态地质要素研究；②油气系统动态地质作用（可以通过地史、热史、生烃史、排烃史、运移聚集史模拟再现）研究；③油气系统的关键时刻与事件组合关系研究。盆地模拟已形成了系统化、模型化、定量化的动态模拟软件，用盆地模拟技术实现油气系统动态数值模拟是现实可行的捷径。在盆地综合模拟系统基础上，按照油气系统的研究内容和成图表达方式，建立了油气系统动态分析模拟软件系统，具有进行四方面分析模拟的功能①背景研究，利用平衡剖面、层序地层模拟以及构造热模拟等方法，综合研究油气系统的背景、单个油气系统静态地质要素等；②动态地质作用模拟研究，研究油气系统的地史、热史、生烃史、排烃史、运聚史过程；③关键时刻与事件组合关系研究；④油气资源量估算与有利目标评价。图2参6（张庆春摘）     

珠江口盆地地温场特征及构造-热演化

位于南海北缘的珠江口盆地作为中国海洋油气勘探的重点区域，具有良好的油气勘探前景。利用钻井地热测量数据分析了珠江口盆地现今地温场特征，利用古温标反演和拉张盆地模型正演相结合的方法定量揭示了盆地新生代以来的热演化史，并对比分析了浅水区和深水区构造-热演化的差异及主控因素，总结了不同地热地质条件对油气生成和富集的影响。研究结果表明，珠江口盆地具有"热盆"特征，地温梯度高。地温梯度值的总体变化趋势表现为从浅水区向深水区逐渐增高，与地壳和岩石圈向南减薄趋势一致。珠江口盆地始新世以来经历了两期裂陷拉张作用，其基底热流值表现为幕式升高的特征。浅水区珠一坳陷达到最高古热流的时间相对较早（约为33.9 Ma），而盆地深水区（白云凹陷、荔湾凹陷）裂陷拉张时间可以持续到23 Ma，随后才进入裂后热沉降期，盆地基底热流开始降低。白云凹陷磷灰石裂变径迹（AFT）热史模拟显示晚期约在5 Ma以来存在一期古地温快速增加，这可能与新构造运动有关。此外，由于深水区拉张强度大，加热时间长，陆坡区的白云凹陷最高古热流要高于陆架区的其他凹陷。     

流体包裹体在准噶尔盆地油气资源评价中的应用

本文通过对准噶尔盆地两口钻井及一条石炭系地表剖面中的石英脉、石英-方解石脉流体包裹体岩相学及测温的研究,结合镜面反射率资料,论述了该区生油层热历史及其油气形成、演化特征。对石英-方解石脉流体包裹体测温及其地质意义作了深入的讨论。      

准噶尔盆地热演化历史模拟

根据磷灰石裂变径迹和镜质体反射率(Ｒ。)动力学模型模拟了准噶尔盆地腹部莫索湾、陆南和盆地南缘等地区的地温演化历史。研究结果表明,尽管准噶尔盆地现今的地温较低,但由于受构造运动的影响,各地质历史时期的地温演化不同,盆地的古地温较现今地温高。特别是在古生代和三叠纪,地温梯度很高。古生代的地温梯度平均大于38℃／ｋｍ,中生代三叠纪的地温梯度仍很高,为34．6－41℃／ｋｍ．侏罗纪的地温梯度变化较大,这可能与该时期的构造运动频繁有密切关系。白垩纪以后盆地的地温梯度演化基本不变,与现今相当。     

BURIAL,TEMPERATURE AND MATURATION HISTORY OF CRETACEOUS SOURCE ROCKS IN THE NW PERSIAN GULF,OFFSHORE SW IRAN: 3D BASIN MODELLING

This study presents a 3D numerical model of a study area in the NW part of the Persian Gulf, offshore SW Iran. The purpose is to investigate the burial and thermal history of the region from the Cretaceous to the present day, and to investigate the location of hydrocarbon generating kitchens and the relative timing of hydrocarbon generation/migration versus trap formation. The study area covers about 20,000 km² and incorporates part of the intra‐shelf Garau‐Gotnia Basin and the adjacent Surmeh‐Hith carbonate platform. A conceptual model was developed based on the interpretation of 2700 km of 2D seismic lines, and depth and thickness maps were created tied to data from 20 wells. The thermal model was calibrated using bottom‐hole temperature and vitrinite reflectance data from ten wells, taking into account the main phases of erosion/non‐deposition and the variable temporal and spatial heat flow histories. Estimates of eroded thicknesses and the determination of heat‐flow values were performed by burial and thermal history reconstruction at various well and pseudo‐well locations. Burial, temperature and maturation histories are presented for four of these locations. Detailed modelling results for Neocomian and Albian source rock successions are provided for six locations in the intra‐shelf basin and the adjacent carbonate platform. Changes in sediment supply and depocentre migration through time were analyzed based on isopach maps representing four stratigraphic intervals between the Tithonian and the Recent. Backstripping at various locations indicates variable tectonic subsidence and emergence at different time periods. The modelling results suggest that the convergence between the Eurasian and Arabian Plates which resulted in the Zagros orogeny has significantly influenced the burial and thermal evolution of the region. Burial depths are greatest in the study area in the Binak Trough and Northern Depression. These depocentres host the main kitchen areas for hydrocarbon generation, and the organic‐rich Neocomian and Albian source rock successions have been buried sufficiently deeply to be thermally mature. Early oil window maturities for these successions were reached between the Late Cretaceous (90 Ma) and the early Miocene (18 Ma) at different locations, and hydrocarbon generation may continue at the present‐day.     

鄂尔多斯盆地的地热场特征与有机质成熟史

根据现个地温梯度及镜质体反射率测定结果,反演了鄂尔多斯盆地现今大地热流分布,在综合研究盆地古、今地热场特征的基础上,对地热场的影响因素进行了统计分析,并指出了主要影响因素的特点.结合构造—沉积演化史,探讨了盆地不同阶段、不同地区的有机质成熟史.      

盆地热演化史的计算机数值模拟

热史模拟是盆地模拟的模拟，正反演数值模拟通过不同的路径来恢复盆地热史，而磷灰石－锆石径迹古地温作为一种较可靠的地质温度计提供了新的古地温信息，三者相互比较和验证，有助于正确认识盆地古地温，本文将正，反演数值模拟方法应用于鄂尔多斯盆地古生界热演化史的恢复中，并和磷灰石－锆石径迹古地温相互比较和验证，取得了三者近于一致的结果。