Salinity reflux and dolomitization of southern Australian slope sediments: the importance of low carbonate saturation levels

Anomalously saline waters in Ocean Drilling Program Holes 1127, 1129, 1130, 1131 and 1132, which penetrate southern Australian slope sediments, and isotopic analyses of large benthic foraminifera from southern Australian continental shelf sediments, indicate that Pleistocene–Holocene meso‐haline salinity reflux is occurring along the southern Australian margin. Ongoing dolomite formation is observed in slope sediments associated with marine waters commonly exceeding 50‰ salinity. A well‐flushed zone at the top of all holes contains pore waters with normal marine trace element contents, alkalinities and pH values. Dolomite precipitation occurs directly below the well‐flushed zone in two phases. Phase 1 is a nucleation stage associated with waters of relatively low pH (ca 7) caused by oxidation of H₂S diffusing upward from below. This dolomite precipitates in sediments < 80 m below the sea floor and has δ¹³C values consistent with having formed from normal sea water (? 1‰ to + 1‰ Vienna Pee Dee Belemnite). The Sr content of Phase 1 dolomite indicates that precipitation can occur prior to substantial metastable carbonate dissolution (< 300 ppm in Holes 1129 and 1127). Dolomite nucleation is interpreted to occur because the system is undersaturated with respect to the less stable minerals aragonite and Mg‐calcite, which form more readily in normal ocean water. Phase 2 is a growth stage associated with the dissolution of metastable carbonate in the acidified sea water. Analysis of large dolomite rhombs demonstrates that at depths > 80 m below the sea floor, Phase 2 dolomite grows on dolomite cores precipitated during Phase 1. Phase 2 dolomite has δ¹³C values similar to those of the surrounding bulk carbonate and high Sr values relative to Phase 1 dolomite, consistent with having formed in waters affected by aragonite and calcite dissolution. The nucleation stage in this model (Phase 1) challenges the more commonly accepted paradigm that inhibition of dolomitization by sea water is overcome by effectively increasing the saturation state of dolomite in sea water.     

用储层岩石抽提物的饱和烃色谱指纹识别油气层

利用储层岩石抽提物的饱和烃色 质总离子图的指纹特征判识储层的流体（油、气）类型。油层或油饱和的储层,饱和烃色 质总离子流图的特征是正构烷烃碳数分布宽,碳数分布在C₁₅～C₃₈之间,与原油样品的正构烷烃碳数分布相似;凝析气层的正构烷烃碳数分布略窄一些,碳数分布在C₁₅～C₃₅之间,低碳数（小于C₂₁）的正构烷烃相对于油层富集,高碳数（大于C₂₁）的正构烷烃丰度明显低于油层;干气层的正构烷烃碳数分布最窄,碳数分布在C₁₅～ C₂₈之间,只有低碳数的正构烷烃,高碳数的正构烷烃丰度极低。据此可用来识别油层、凝析气层和干气层,也可用于一些测井资料不全或测井质量差的老井的油气层复查、测井难以识别的火成岩油气层的识别,还可用于地层评价,为油气酸化层位的优选提供科学依据。     

Research Advances and Exploration Significance of Large-area Accumulation of Low and Medium Abundance Lithologic Reservoirs

In recent years, a series of large low and medium abundance oil and gas fields are discovered through exploration activities onshore China, which are commonly characterized by low porosity-permeability reservoirs, low oil/gas column height, multiple thin hydrocarbon layers, and distribution in overlapping and connection, and so on. The advantageous conditions for large-area accumulation of low-medium abundance hydrocarbon reservoirs include： （1） large （fan） delta sandbodies are developed in the hinterland of large flow-uncontrolled lake basins and they are alternated with source rocks extensively in a structure like ＂sandwiches＂; （2） effective hydrocarbon source kitchens are extensively distributed, offering maximum contact chances with various sandbodies and hydrocarbon source rocks; （3） oil and gas columns are low in height, hydrocarbon layers are mainly of normal-low pressure, and requirements for seal rock are low; （4） reservoirs have strong inheterogeneity and gas reservoirs are badly connected; （5） the hydrocarbon desorption and expulsion under uplifting and unloading environments cause widely distributed hydrocarbon source rocks of coal measures to form large-area reservoirs; （6） deep basin areas and synclinal areas possess reservoir-forming dynamics. The areas with great exploration potential include the Paleozoic and Mesozoic in the Ordos Basin, the Xujiahe Formation in Dachuanzhong in the Sichuan basin, deep basin areas in the Songliao basin etc. The core techniques of improving exploration efficiency consist of the sweetspot prediction technique that focuses on fine characterization of reservoirs, the hydrocarbon layer protecting and high-speed drilling technique, and the rework technique for enhancing productivity.     

甘肃庆城庄19井区上三叠统延长组长82亚油层组低渗透储层的地质特征

长82亚油层组是甘肃庆城地区庄19井区上三叠统延长组中储集砂岩相对富集的层位,但砂岩低渗透性的特点显著,成为影响该区石油储产量增长的主要地质因素。结合前人的相关工作,通过钻井岩心观察、测井曲线分析、储层岩石实验测试等工作,详细地分析了庄19井区长82亚油层组低渗透储层的地质特征,认为沉积微相和压实作用、胶结作用是控制低渗透性储集砂岩发育和分布的主要地质因素,寻找以水下分流河道微相为代表的有利储集相带砂岩体是油气勘探的重要方向。     

英买力凝析气田群区巴什基奇克组-库姆格列木群 层组划分与对比研究

英买力凝析气田群区层组划分与对比研究是该地区陆相地层油气藏地质和开发工程中最基本和最重要的精细地质研究内容之一,也是急需解决的关键技术难题之一。本次研究采取"取心标准井出发,岩心标定测井,寻找辅助标志层,进行旋回对比、分级控制,将隔夹层纳入到同一沉积旋回进行识别、划分对比,以隔层确定小层,并兼顾‘就近、闭合’的原则"展开层组划分与对比,重新确定出更适用于气田开发的气层组、砂层组、小层等划分单元。而对可以作为层组划分与对比辅助手段的白垩系与古近系不整合界面、库姆格列木群底砂岩段顶界以及层组中的隔夹层等的识别,为层组的精细划分对比提供了重要保证,很好地解决了巴什基奇克组、库姆格列木群的层组划分问题,对英买力地区凝析气藏的后期开发等问题具有积极的指导意义。     

天津市蓟县系雾迷山组热储层水位动态变化及趋势预测研究

通过对天津市蓟县系雾迷山组热储层地下水位动态规律的分析,利用LUMPFIT软件预测了在不同开采量下未来水位的变化规律。结果表明,水位呈逐年下降的趋势,但由于回灌量的增加,水位下降速率明显减小。     

塔里木盆地凝析气田的地质特征及其形成机制

塔里木盆地凝析油气资源丰富,已发现了二十余个凝析气田,包括库车坳陷的陆相油气来源的凝析气田和台盆区海相烃源岩来源的凝析气田;储层有碎屑岩,也有碳酸盐岩;时代自奥陶系至新生代均有分布。这些凝析气田的气油比分布在600~19900m³/m³,凝析油含量40~750g/m³;储层温度在78~155℃;地层压力在37~111MPa。研究认为,塔里木盆地凝析气藏的成因类型可以分为原生凝析气藏和次生凝析气藏。其中,以库车坳陷迪那2凝析气田为代表的煤系烃源岩在高演化阶段(镜质体反射率Ro为1.2%~2.0%),即凝析油和湿气生成带所形成的原生腐植型凝析气藏或煤成型凝析气藏。次生凝析气藏包括两类:陆相油气来源的多期充注,晚期干气对早期油藏发生混合改造,形成了以牙哈为代表的陆相油气成因的次生凝析气藏;以海相油气来源,多期油气充注与晚期干气气侵,造成蒸发分馏,在运移、聚集和成藏过程中烃体系分异、富化,发生反凝析作用,从而导致次生凝析气藏的形成。随着塔里木盆地勘探向深层转化,地层的温度和压力逐渐增高,烃类演化程度的升高,不同生烃阶段的烃体系混合也将更为普遍,次生凝析气藏也将更为普遍,因此,以海相油气来源的次生成因型凝析气藏将成为勘探的主体。     

气井水力压裂有效缝长评估及影响因素研究

为了准确确定气井压后有效缝长及其影响因素,提高川西须家河气藏水力压裂针对性,对于具备生产历史拟合条件的气井,利用数值模拟软件进行了生产历史拟合获得有效水力裂缝缝长,与采用净压力拟合方法获得的水力裂缝支撑缝长进行对比和拟合,获得了有效缝长和支撑缝长的关系式,计算了川西须家河储层单井压后有效缝长;采用灰色关联分析理论分析了各个参数对有效缝长的影响程度和对压裂设计的启示。结果表明：压后有效缝长与支撑缝长具有较强相关性(Le=00584 Lp1359 3),有效缝长明显比支撑缝长短;施工参数(特别是用液量)是影响须家河储层有效缝长的关键,而储层和隔层间应力差则是影响有效缝长的重要客观因素。该研究方法为水力压裂压后评估和提高压裂设计水平提供了较好的借鉴。     

漳州热田地下热水的循环深度

漳州热田是我国东南沿海地区目前所见温度(121.5℃)最高的一个。热田地热地质、地球化学以及地温场的研究结果表明,漳州热田属于深循环对流型热田。为了计算热田的热水循环深度,本文采用管道模型的方法,利用热田中心钻孔的测温资料计算地下热水上涌的流速,利用热田内水化学资料计算热储温度,然后用图解法求出漳州热田热水的循环深度为3.4—4.0 km,为漳州热田的成因分析和热水资源的评价提供了依据。     

川西裂缝性致密碎屑岩气藏高渗区成因机理及预测

川西深层上三叠统须家河组二段致密碎屑岩气藏非均质性极强,裂缝网络与相对优质储层叠加形成的高渗区分布预测是钻井获得高产稳产的技术关键。通过地表露头调查、钻井资料统计分析及地震地质综合研究,剖析了高渗区地质成因机理,认为在砂岩及岩性相变带、相对薄层及地层厚度突变带、优质储层发育区、强构造褶皱变形区、断裂附近等易于形成裂缝及高渗区。通过高渗区储层测井及波阻抗特征、地震响应特征对比分析、模型正演等方法,建立了“杂乱弱反射”地震暗点识别模式,利用吸收处理、像素成像、三维可视化等地震技术手段,预测了高渗区分布,解释了各高渗区地质成因,钻井验证了预测结果。