轮南地区压力场演化及其成藏意义

选择轮南主体区剖面七条和临近凹陷剖面两条,利用压力数值模拟手段,对轮南地区的压力场演化进行了恢复和模拟。结合实测压力资料和钻井资料,发现部分地区石炭系和上奥陶统中存在弱超压、寒武系在凹陷内存在超压。通过分析,石炭系超压在轮南主体区主要是水热增压作用和泥岩转换作用造成的,在凹陷内则可能主要由于欠压实引起。上奥陶统内部的超压和石炭系在形成时间、特征和发育机理上相似,不过轮南地区上奥陶统覆盖区域较少。寒武系超压和三个成藏期相对应,在凹陷内形成明显的三期超压现象,以喜山期超压幅度最大。整体上看,石炭系和上奥陶统弱超压,对成藏动力方面贡献不大,但是超压的形成增强了该层的封闭性,对喜山期天然气成藏有重要影响。寒武系超压为油气初次运移提供了动力,但是超压幅度有限,推测其在油气二次运移过程中贡献不大。     

西湖凹陷钻前压力预测技术及应用

西湖凹陷普遍发育超压,钻井工程中发现,发育超压地层的钻井成本明显大于发育常压地层的井,亟需建立相关钻前压力预测技术,提高钻前压力预测精度,保障钻井安全和降低钻井成本。笔者首先对前期钻前压力预测误差大的原因进行了分析,发现压力计算参数精度低、压力计算模型不适应是导致压力预测精度低的原因,因此,在明确区域"生烃增压"成因背景下,建立了一套以高精度速度处理为基础,优选Bowers计算模型并通过经验系数校正的钻前压力预测技术。该技术在西湖凹陷取得了良好的应用效果。     

白云凹陷地球物理场及深部结构特征

珠江口盆地白云凹陷是南海最具代表性的第三系深水陆坡沉积区。以穿过白云凹陷中部的一条深反射地震剖面(14s)为研究基础，采用综合地球物理研究方法分析了该区地球物理场特征，根据重力异常平面等值线勾画了白云凹陷的形态，并提取该测线相对应的重磁剖面数据，利用重磁资料和地震剖面进行了综合反演。以深剖面地震资料建立了地质模型，利用所得的重力数据进行了研究深部结构的正演拟合，实测与计算值拟合较好，支持中生代俯冲洋壳存在的观点；同时结合地震资料对深部结构进行了分析，该区莫霍面由陆向海抬升，呈阶梯状变化，地壳厚度逐渐减薄，具有大陆边缘陆壳向洋壳过渡的特征。根据地质模型还进行了变密度综合反演拟合来分析基底岩性特征，该区基底主要为中酸性岩浆岩，部分为变质岩和基性火山岩，岩石密度由陆向洋逐渐减小，磁性体分布不均。     

沧东凹陷沙河街组地震地层分析

利用地震资料及地质、钻井资料,对沧东凹陷沙河街组地震反射剖面进行了地震界面及地震层序划分,对其反射特征进行了较详细的描述。在进行地震相及沉积相划分和分析的基础上,对各层序的沉积特征进行了分析,这为该地区沉积盆地的油气生储盖特征提供了基础资料[1]。     

BZ13-1油田井壁稳定性研究及应用

位于渤海中部海域的BZ13-1油田在前期钻井中存在溢流、井漏、阻卡等较多复杂问题,制约了钻井速度。井壁稳定的力学分析方法主要利用钻井资料、测井资料、录井资料等,分析地层压力、地应力、地层强度参数的分布规律,结合岩体强度准则计算坍塌压力与破裂压力,得出钻井安全密度窗口。通过对BZ13-1油田井壁稳定性进行分析,得出了高压层、易漏失层、易坍塌层位置,并据此对开发井进行井身结构设计,分析结果在开发井钻井中取得了良好的应用效果,有效减少了钻井复杂问题。     

南海北部小型海陆过渡相断陷地震相分析及沉积充填演化史研究——以琼东南盆地崖南凹陷崖城组为例

南海北部琼东南盆地众多凹陷存在有海陆过渡相沉积,选取浅水区井孔资料相对较多的小型断陷即崖南凹陷作为研究对象,在等时地层格架内,对该凹陷海陆过渡期崖城组地震相进行深入解剖;并综合利用经典沉积模式以及凹陷周缘浅水地区井孔资料来建立地震相与沉积相之间的关系,赋予地震相以地质意义,进而预测了凹陷无钻井资料地区各种沉积相的展布,...     

车镇凹陷北部陡坡带砂砾岩体识别与储层物性预测

车镇凹陷陡坡带沙三段砂砾岩扇体发育,但目前对砂砾岩体横向展布范围及砂砾岩体边界的划分尚不清楚,储层物性难以预测。首先,利用相干分析技术开展砂砾岩扇体沉积相的划分,明确了扇体的展布规律、分布范围、划清了砂砾岩扇体的边界。然后,利用声波、速度谱等资料探讨了沙三下亚段(Es3x)地层压力情况,认为Es3x存在欠压实超压带,车镇凹陷欠压实超压带的发现为寻找沙三段砂砾岩扇体储层物性良好发育区指明了方向。最后,利用地震高频能量衰减检测技术对储层物性进行了预测。通过地震高频能量衰减梯度法预测的储层物性良好发育区,位于研究区欠压实超压区带内,用地震能量高频波段的衰减特征不但可预测不同井位的储层物性,还可根据连井衰减梯度剖面的变化规律预测地震高频波段高衰减区的延伸范围。高频能量衰减梯度法预测的储层物性良好发育区带与实钻结果吻合度好。     

东海西湖凹陷温压系统与油气成藏

针对西湖凹陷存在异常温压系统的现象,利用钻井测温资料、测井声波时差压力、流体包裹体、镜质体反射率和磷灰石裂变径迹等资料对西湖凹陷的温压系统特征、类型及其对油气成藏的影响进行了系统研究。结果表明,西湖凹陷不同构造单元具有各异的温压场特征;西湖凹陷不同构造单元的温压系统类型不尽相同,其中保散斜坡带和三潭深凹为高压型温压系统,浙东背斜带为常压型温压系统;西湖凹陷不同温压系统具有各异的流体流动样式和油气运聚规律;浙东中央背斜带内的流体能量相对最低,是研究区内有利的油气运聚区域。     

台湾海峡西部地震地层分析

利用在台湾海峡西部采集的近万公里地震反射资料及围区地质、钻井及地震资料,对晋江凹陷和九龙江凹陷地震反射剖面进行了较详细的描述与分析,以及地震层序和地震相划分,对各地震层序及地震相分别进行了地质年代与沉积相探讨,并首次把九龙江凹陷T_3~0—T_g超层序解释为中生代地层的不同见解,这对研究该区海域沉积史、生油气史、油气储层和盖层,以及进一步开展油气勘探有十分重要的意义。     

琼东南盆地气烟囱构造特点及其与天然气水合物的关系

气烟囱是由于天然气(或流体)垂向运移在地震剖面上形成的异常反射,是气藏超压、构造低应力和泥页岩封隔层综合作用而形成。气烟囱在形成过程中携带大量富含甲烷气的流体向上运移到天然气水合物稳定带,其形成之后仍可作为后期活动的油气向上运移的特殊通道。在中中新世后,气烟囱是琼东南盆地气体向上运移的通道。地震识别出的似海底反射(BSR)分布区存在大量的气烟囱构造,通过速度、泥岩含量、流体势等属性参数及钻井资料,判断该烟囱构造为有机成因的泥底辟型烟囱构造。     

Present-day stress and pore pressure fields in the Cuu Long and Nam Con Son Basins, offshore Vietnam

Knowledge of the in situ, or contemporary stress field is vital for planning optimum orientations of deviated and horizontal wells, reservoir characterization and a better understanding of geodynamic processes and their effects on basin evolution.This study provides the first documented analysis of in situ stress and pore pressure fields in the sedimentary formations of the Cuu Long and Nam Con Son Basins, offshore Vietnam, based on data from petroleum exploration and production wells.In the Cuu Long Basin, the maximum horizontal stress is mainly oriented in NNW–SSE to N–S in the northern part and central high. In the Nam Con Son Basin, the maximum horizontal stress is mainly oriented in NE–SW in the northern part and to N–S in the central part of the basin.The magnitude of the vertical stress has a gradient of approximately 22.2 MPa/km at 3500 m depth. Minimum horizontal stress magnitude is approximately 61% of the vertical stress magnitude in normally pressured sequences.The effect of pore pressure change on horizontal stress magnitudes was estimated from pore pressure and fracture tests data in depleted zone caused by fluid production, and an average pore pressure–stress coupling ratio (ΔS_h/ΔP_p) obtained was 0.66. The minimum horizontal stress magnitude approaches the vertical stress magnitude in overpressured zones of the Nam Con Son Basin, suggesting that an isotropic or strike-slip faulting stress regime may exist in the deeper overpressured sequences.     

Compaction of diagenetically altered mudstones – Part 2: Implications for pore pressure estimation

Diagenetically altered mudstones compact mechanically and chemically. Consequently, their normal compaction trends depend upon their temperature history as well as on the maximum effective stress they have experienced. A further complication is that mudstones are commonly overpressured where clay diagenesis occurs, preventing direct observation of the hydrostatic normal compaction trend. A popular way to estimate pore pressure in these circumstances is to calculate the sonic normal compaction trend in a well with a known pressure–depth profile by applying Eaton's method in reverse, and then to estimate pore pressure in offset wells using Eaton's method conventionally. We tested this procedure for Cretaceous mudstones at Haltenbanken. The results were inconsistent because the sonic log responds differently to disequilibrium compaction overpressure and unloading overpressure, and their relative contributions vary across the basin. In theory, a two-step method using the density and sonic logs could estimate the contributions to overpressure from disequilibrium compaction and unloading. The normal compaction trend for density should be the normal compaction trend at the maximum effective stress the mudstones have experienced, not at hydrostatic effective stress. We advocate the Budge-Fudge approach as a starting point for pore pressure estimation in diagenetically altered mudstones, a two-step method that requires geological input to help estimate the overpressure contribution from disequilibrium compaction. In principle, the Budge-Fudge approach could be used to estimate the normal compaction trend for mudstones at the maximum effective stress they have experienced, and so form the basis of the full two-step method through the use of offset wells. Our initial efforts to implement the full two-step method in this way at Haltenbanken produced inconsistent results with fluctuations in estimated pore pressure reflecting some of the fluctuations in the density logs. We suspect that variations in the mineralogical composition of the mudstones are responsible.     

澳大利亚大澳湾盆地塞杜纳坳陷构造演化及构造特征分析

澳大利亚大澳湾盆地是目前世界上为数不多的低勘探程度大型沉积盆地,其中塞杜纳坳陷是近几年各大石油公司高度关注的区域。受地震资料品质的影响,前人对塞杜纳坳陷的地层结构、构造演化和构造样式方面的研究还不清楚。本文以重处理二维地震资料为基础,开展大面积的构造解释,通过"回剥法"平衡剖面恢复和重建了塞杜纳坳陷的构造演化历史,与其他类似构造和沉积背景的被动陆缘盆地类比确立了塞杜纳坳陷的双重重力滑脱构造模式。在对塞杜纳坳陷构造特征进行解析的基础上,结合对塞杜纳坳陷的构造差异性分析,总结出塞杜纳坳陷发育的3类共8种主要的圈闭类型,并指出有利圈闭类型发育带的分布,为下步勘探指明了方向。     

西非盐下裂谷构造特征及其地质意义

西非海岸盆地盐下裂谷随着近年来油气新发现显示出巨大的勘探潜力。基于区域地震资料,对盐下裂谷构造层系开展解释,并对裂谷构造特征开展了深入探讨。研究表明,西非盐下盆地具有早期裂陷、晚期坳陷的构造特征。平面上具有内裂谷带—中央隆起带—外裂谷带东西向隆坳相间的一级构造格局,在外裂谷带又识别出了一系列凸起和凹陷二级构造单元。裂谷隆坳格局受断层控制,具有“东西分带、南北分段”的平面特征。裂谷期构造特征指示出西非陆内裂谷作用发生具有北早南晚、持续时间北长南短板块构造意义。同时裂谷演化过程中衍生重要的含油气系统,具有重要的油气勘探意义。     

Is stress-insensitive chemical compaction responsible for high overpressures in deeply buried North Sea chalks?

Chalk compaction is often assumed to be controlled by a combination of mechanical and effective stress-related chemical processes, the latter commonly referred to as pressure solution. Such effective stress-driven compaction would result in elevated porosities in overpressured chalks compared with otherwise identical, but normally pressured chalks. The high porosities that are frequently observed in overpressured North Sea chalks have previously been reported to reflect such effective stress-dependent compaction.However, several wells with deeply buried chalk sequences also exhibit low porosities at high pore pressures. To investigate the possible origins of these overpressures, basin modeling was performed in a selected well (NOR 1/3-5) offshore Norway. This modeling was based on both effective stress-driven mechanical porosity reduction, which enables modeling of disequilibrium compaction, and on stress-insensitive chemical compaction where the porosity reduction is caused by thermally activated diagenesis.The modeling has demonstrated that the present day porosities and pore pressures of the chalks could be successfully replicated with mechanical porosity loss as the only process leading to chalk porosity reduction. However, the modeled porosity and fluid pressure history of the sediments deviated significantly from the porosity and pore pressure versus depth relationships observed in non-reservoir North Sea chalks today. To the contrary, modeling which was based on thermally activated porosity loss due to diagenesis (as a supplement to mechanical compaction), resulted in modeled chalk histories that are consistent with present day observations.It was therefore inferred that disequilibrium compaction could not account for all of the pore pressure development in overpressured chalks in the study area. The observation that modeling including temperature-controlled diagenetic porosity reduction gave plausible results, suggests that such porosity reduction may in fact be operating in chalks as well as in clastic rocks. If this is correct, then improved methods for pore pressure identification and fluid flow analysis in basins containing chalks should be developed.     

Pore pressure within dipping reservoirs in overpressured basins

To predict reservoir pore pressure, we present a one-dimensional flow model that captures complicated two- and three-dimensional flow present in a dipping permeable reservoir encased in overpressured mudrock. The model incorporates the variation of mudrock permeability with effective stress and includes the effect of reservoir geometry. We find that reservoir pressure is lower when stress-dependent mudrock permeability is assumed relative to the case of constant mudrock permeability. Increased structural relief further reduces the reservoir pressure relative to the far-field pressure and increased effective stress (pore pressure is lower relative to the overburden) results in increased reservoir pressure relative to the far-field pressure. If a large fraction of the reservoir area is in deeper areas where the mudrocks are more overpressured, then the relative pressure is higher than cases where the reservoir area remains constant with depth. The model results compare favorably both to pressures predicted by a more complex numerical model that simulates basin evolution and to field observations in the Bullwinkle Basin (Green Canyon 65, Gulf of Mexico). Our model provides a quick workflow to predict excess pressures in dipping reservoirs encased in mudrock within mechanically-compacted basins. It can be used to analyze trap integrity, understand hydrocarbon migration, and improve drilling safety.     

台湾海峡盆地九龙江凹陷火成岩发育特征及其油气地质意义

基于二维地震剖面的精细地质解释,并结合磁力和钻井资料分析,开展了九龙江凹陷火成岩发育特征、岩浆活动和区域构造与盆地演化关系及其油气地质意义的研究。分析认为,九龙江凹陷经历了始新世中晚期、中新世中晚期二期火山活动,火成岩在地震剖面上主要表现为板状、锥状及块状三种地震相类型,钻井主要揭示了喷发、侵入及火山碎屑三大类型火成岩,它们的发育与分布是区域性构造事件和盆地演化相作用的结果。始新世中晚期火山活动产生的高温有利于烃源岩在短期内经历高温的催化改造而生成油气,形成的火成岩体岩墙面可以增加和改善凹陷中央区油气向西部斜坡的运移,该火成岩附近区的一些圈闭在成岩期受热液蚀变的影响,储层孔、渗性得到改善的同时也会致使储层发生不同程度的变质,在今后的勘探开发中是一个值得关注的问题。     

Pore pressure assessment from well data and overpressure mechanism: Case study in Eastern Tunisia basins

Abstract

Independent and complementary methods were used for pore pressure assessment in the eastern Tunisian basins. Drilling data and surveys allow settling the pore pressure profile in these basins. The main used parameters are mud weights, formation pressure surveys, drilling parameters, well logs, fluids exchange with formation and borehole issues. In the eastern Tunisia platform, the pore pressure profiles show changes in overpressure magnitude in all the three dimensions of the basin (location and depth/stratigraphy). We highlighted two overpressure intervals form bottom to top: The late Cretaceous in the North-eastern part, and the Tertiary overpressure interval hosted in the Palaeocene to Miocene series. The structural analysis of overpressure location shows that the Tertiary interval is likely to have originated in a disequilibrium compaction in Cenozoic grabens. Pore pressure cross sections and maps confirm the link between active normal faults that segmented the basin to grabens and highs and pore pressure anomalous area. In the Senonian interval, we noted mature source-rocks that can explain the overpressure in the late Cretaceous interval. In addition, the recent to active compressive tectonics may have contributed to both pore pressure anomaly generations. The fluid overpressures characterization in the eastern Tunisian sedimentary basins helps in hydrocarbons exploration. Indeed, the overpressure interval in the reservoir levels stimulates and improves the production in the oilfields and contributes to hydrocarbon trapping. Moreover, the adequate prediction of pore pressure profile contributes to reduce drilling cost and enhance the drilling operations safety.