Estimation of Curie-point depths,geothermal gradients and near-surface heat flow from spectral analysis of aeromagnetic data in the Loum – Minta area (Centre-East Cameroon)

The current study deals with an estimate the Curie point depth, Heat flow and geothermal gradient from spectral analysis of aeromagnetic data in the Loum – Minta area, Centre-East Cameroun. Aeromagnetic data reduce to equator was divided into 5 blocks. All of the blocks overlapped with adjoining blocks by 50 percent and each block analyzed using the spectral centroid method to obtain depth to the top, centroid and bottom of magnetic sources. The depth values were subsequently used to evaluate the Curie-point depth (CPD), geothermal gradient and near-surface heat flow in the study area. The result shows that the CPD varies between 5.22 and 14.35?km with an average of 9.09?km, the geothermal gradient varies between 40.42 and 111.11?°C/km with an average of 72.24?°C/km, and the resulting heat flow varies between 101.05 and 277.77?mW?m^?2 with an average of 180.59?mW?m^?2. Such heat flow values are suggestive of anomalous geothermal conditions and are recommended for detailed geothermal exploration.     

塔里木盆地大庆区块壳内地温场计算及应用分析

在简要介绍航资料应用于区域壳内地温场研究的方法原理之后,通过塔里木盆地大庆区块的实算应用,分析研究了壳内地温场特征及其对油气生成的影响。指出利用航磁资料反演居里面深度,进而推算壳内平均地温梯度,是研究地温场的有效方法,为大庆区块地壳结构、地壳热状态的研究及生油潜力评估提供了重要依据。     

查干凹陷现今地温场研究及其油气地质意义

查干凹陷是银-额盆地最具油气勘探潜力的凹陷,文中应用9口井的测温资料,计算了查干凹陷的地温梯度、大地热流,分析了查干凹陷地温梯度平面分布特征。研究结果表明:查干凹陷具有稳定区域的中等地温型地温场特征,其平均地温梯度为3.36°C/100 m,平均估算大地热流为54.04 mW/m2;凹陷地温梯度的分布呈现毛敦次凸最高,东部次凹次之,西部次凹最低的特征;其分布与基底埋深相关,还与查干凹陷区巨厚沉积盖层和凹陷四周凸起之间产生的"热折射"效应作用有关。另外,查干凹陷烃源岩的成熟度受古地温影响。研究成果为查干凹陷及银-额盆地其他凹陷的烃源岩生烃评价提供了地温资料。     

Discussion about “estimation of curie depth,geothermal gradient and near-surface heat flow from spectral analysis of aeromagnetic data in the loum-minta area (centre-east cameroon)”

Backgroundthis paper reviews the results obtained from recent studies mentioning the crustal architecture in Cameroon. It also discusses the study of [1] “Estimation of Curie depth, geothermal gradient and near-surface heat flow from spectral analysis of aeromagnetic data in the Loum-Minta area (Centre-East Cameroon)”. The paper published by [1] is an application of the spectral method for the determination of Curie depths, followed by interpretations on the local thermal structure (thermal gradient, heat flux) of the crust. However, some outliers are remarkable and depend at first analysis on a bad mesh of the data following a windows of 27.75 * 27.75 km. Similarly, the failure to take into account the various parameters (seismic, geological, tectonic) which would help to better calibrate the results.Discussionwith this communication, we would like to mention and clarify some errors in the paper published by [1] based on a global review of thermal behaviour of the crust.SummaryIt is strongly recommended that information on regional geology and seismicity be used to estimate the Curie depths and that other independent data be integrated to determine the thermal and mechanical behaviour of the crust in Cameroon.     

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。     

利用航磁资料研究楚雄盆地地温并预测油气远景区

本文利用航磁资料估算了楚雄盆地居里面深度,进一步估算了该盆地不同地区的平均地温梯度,并对可能含油气地区进行了预测。     

四川盆地地温梯度及几个深并的热流值

利用四川盆地100余口石油探井的地温资料,编制了地温梯度等值线图;并利用这些深井岩芯进行了岩石热导率的测定,获得各时代地层热导率数据58个;又选取在同一研究段既有可靠地温梯度资料又有岩芯热导率测试资料的6口深井进行了热流值计算。地温梯度及热流值均以川中为最高,向四周降低。     

松辽盆地古地温恢复

通过多种古地温研究方法恢复了松辽盆地的古地温及古地温梯度 ,研究结果表明松辽盆地古地温高于今地温 ,白垩纪末的地温梯度及大地热流值可达 4 2 6～ 4 80℃ 10 0m和 95～ 10 7mW m2 ,远高于现今地温梯度 3 70℃ 10 0m及大地热流值 69mW m2 。烃源岩热演化程度主要受古地温控制 ,在白垩纪末达到最大古地温 ,以后持续抬升剥蚀和大地热流值衰减、降温使生烃作用减弱或停止。依安组以来的再沉积厚度小 ,不能引起二次生烃     

海上高温高压井环空ECD精细预测模型

为了准确预测高温高压井环空ECD,基于高温高压下钻井液流变性测试数据,利用多元非线性回归得到了钻井液密度和流变参数计算模型。通过将钻井液密度和流变参数计算模型与井筒传热模型耦合,建立高温高压井环空ECD精细预测模型。相比Drillbench软件计算结果,该模型更接近于实测PWD数据,误差更小。实例井计算结果表明,循环钻进过程中,下部环空温度不断降低,钻井液密度和稠度系数受温度影响不断增加,导致环空ECD不断增加;钻井液排量与地温梯度是影响环空ECD分布的关键因素,排量越大,环空压耗越大,进而环空ECD也越大;地温梯度直接影响环空温度分布,地温梯度的增加将导致环空ECD的不断降低。      

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.     

南海北部深水区地热特征及其成因

对392个地温梯度数据和234个大地热流数据的统计结果显示：南海北部深水区地温梯度为2.94～5.22℃/hm,平均为3.91±0.74℃/hm;大地热流值为24.2 ～121 mW/m²,平均为77.5±14.8 mW/m²。南海北部地区现今地温场具“热盆”属性,且深水区比浅水区更“热”。大地热流总体变化趋势为：从陆架到陆坡（从北到南）逐渐增高,且增高趋势与地壳减薄趋势一致,同时,平面上存在显著的局部异常点。新生代岩石圈拉张减薄以及新构造运动引发的岩浆、断裂活动是南海北部深水区具“热盆”特征的根本原因,南北向岩石圈减薄程度控制了大地热流总体变化趋势,新构造运动引发的岩浆与断裂活动则是局部热流异常形成的根本原因。     

地热流对石油生成的控制作用

从有机生油理论来看,温度和热梯度是有机质向石油转化的主要条件。在生油母质的转化过程中,热催化分解是重要的机理。因此,温度和热梯度是颇为重要的。本文用目前世界特大油气田的资料与全球热流值的分布进行对比,并结合我国各油区油层温度资料对石油生成作些初步探讨。     

东海西湖凹陷天外天二井热史恢复

应用结合法和流体包裹体显微测温法对东海西湖凹陷浙东中央背斜带南部天外天二井的地热演化史进行了模拟恢复。结果表明,自渐新世至今,总体表现为古地温梯度呈逐渐降低的趋势,高的古地温梯度有利于烃源岩的成熟演化与烃类生成;坳陷演化阶段的古热流高于区域沉降阶段,升温速率与古热流具有较为明显的"镜像"变化关系。利用结合法与流体包裹体测温法能有效地恢复含油气盆地的热演化历史。     

济阳坳陷沾化凹陷东部热史模拟研究

根据区内钻井测温和镜质体反射率(R^o)资料,采用岩石圈和盆地尺度相结合的分段线性热演化模型,对该区的热史进行了恢复。结果表明:(1)该区自古新世以来,热流的演化形态近似于“马鞍型”,中间有二次回升,但回升的幅度逐渐变小;古新世早期的大地热流值为83.6mW/m²,相当于现代活动裂谷的热流值,今大地热流值为63mw/m²,接近全球大地热流的平均值。(2)该区主力烃源岩经历了持续的受热过程,现今仍处于“生油窗口”内,在深度上具有较大的油气赋存空间,热演化背景十分理想。上述模拟结果可以用渤海湾盆地的裂谷演化模式进行较好的解释,并对胜利油田沾化凹陷的油气勘探工作具有一定的指导作用。     

镜质体反射率剖面反演中的不确定性分析——以鄂西渝东茶园1井为例

由于镜质体反射率与地层温度史之间的高度非线性关系,镜质体反射率剖面反演中存在着不确定性;同时输入参数的误差会进一步导致反演结果的不确定性。反演的不确定性可以借助马尔科夫链—蒙特卡洛(MCMC)方法进行描述和分析。对于鄂西渝东茶园1井,反演结果不确定性表现为:(1)镜质体反射率剖面只能对地层经历最高古温度时的地温梯度及相应的剥蚀量进行有效的约束;(2)对于可接受的反演结果,剥蚀量和古热流之间存在负相关关系;(3)岩石骨架热导率、古地表温度和孔隙度—深度关系等输入参数的误差增加了反演结果的不确定性。反演结果表明,中新生代以来鄂西渝东热流下降约20%,从145 Ma时的(57±4.7)mW/m²到现今的45 mW/m²,相应的剥蚀量约为(3.4±0.4)km。     

Production Allocation in Multi-Layers Gas Producing Wells Using Temperature Measurements With the Application of a Genetic Algorithm

A methodology has been presented of allocating gas rate and associated water to each individual layer using temperature measurements and total surface production of gas and water. In part 1, an analytical forward model has been proposed for wellbore temperature response under two-phase production in a multilayer geometry, using a nodal representation of the well. This model accounts for the formation geothermal gradient, steady-state gas-water flow in the wellbore, friction loss, and Joule-Thomson effect in the wellbore; in contrast to the thermal and physical properties of gas and water, wellbore heat losses due to unsteady heat conduction in the earth, and the mixing of the fluid streams of contrasting temperature. The second part shows the solution technique used to allocate the gas and water rate for each layer. The practical implementation of the new developed production allocation model is examined on data from two actual gas wells with temperature measurements taken from production logging tools recorded in these wells. The results show that the model succeeded to accurately allocate the flow rates of gas and water.     

珠江口盆地南部热演化事件与高地温梯度的成岩响应及其对油气勘探的启示

32.0~16.0 Ma、特别是23.8 Ma以来的构造运动导致南海扩张、岩石圈拉伸减薄,地幔物质和深部热液流体异常活跃,热流背景明显增高,这不仅制约着珠江口盆地南部的沉积环境与沉积作用,同时也对深层砂岩储层的成岩演化过程有着深远的影响。基于显微薄片、镜质组反射率、黏土矿物X射线衍射、流体包裹体、扫描电镜和同位素地球化学等分析手段,结合地温梯度、区域构造背景、储层物性以及CO₂气藏成因等研究成果,揭示了珠江口盆地南部白云凹陷受热演化事件和高地温梯度背景影响的岩石学证据和地质记录,分析了热演化事件和高地温梯度的成岩响应及其对储层成岩演化过程的影响,对比了高、低地温梯度区古近系砂岩储层的成岩作用特征和成岩-孔隙演化过程的差异。高地温梯度区储层的成岩作用与成岩-孔隙演化具有一定的特殊性,深部热流体参与了储层的成岩演化过程,表现出异常热成岩演化,热压实作用总体较强,储层的孔渗性降低明显。高地温梯度区或异常热流区的烃源岩在埋藏较浅处即可达到排烃门限,储层在浅埋藏条件下即可达到较深的成岩作用阶段,易溶矿物更易发生溶蚀而形成次生孔隙发育带。因此,对于热流背景差异明显的地区,应根据热流背景、热演化事件和热异常的不同开展储层分析,以便更准确地预测有利的储集地带和油气聚集区,规避勘探风险。     

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.     

Applicability of the ‘cubic law’ for non-Darcian fracture flow

The influence of inertial effects on the flow of fluids through fractured media is a topic of interest for a number of engineering applications, particularly within the energy sector (e.g. production from gas and oil reservoirs, heat extraction from enhanced geothermal systems, coal-bed methane production). The ‘cubic law’ can provide a simple relationship between the hydraulic aperture of a fracture and its permeability, for Darcian flow of a given fluid. At significant flow velocities, fracture flow becomes non-Darcian, the velocity–permeability relationship becomes non-linear and the cubic law becomes invalid. However, for transitional flow, which retains a component of linearity, the cubic law may still be applicable for initial determination of superficial velocities from flow rate data. Here, the results of fluid flow experiments carried out for air flow through a fractured granite sample under various pressures of confinement are presented. Analysis of the flow data using the cubic law produced valid results for non-Darcian flow cases where inertial effects were modest. The cubic law appears to be applicable for flow cases that, following analysis using the cubic law, return a Forcheimer number < 1.30.     

江苏句容盆地古地温场特征及地层剥蚀厚度

针对多期构造运动叠加盆地的特点,运用镜质体反射率建立了句容盆地三个构造层的古地温梯度,分析了各套古地温系统对地层剥蚀厚度赋存的特征。经与粘土矿物演化温度、裂缝充填物中的包裹体温度、苏北盆地古新统的古地温资料对比以及古地温梯度的成因分析,三套古地温系统符合句容盆地的构造演化史。在此基础上,估算了各构造层的地层剥蚀厚度。