Mud volcanoes in the South Caspian basin: Nature and estimated depth of its products

In paper based on the results of previous studies and latest investigations of mud volcanoes in the South Caspian basin the depth occurrence of fluid, mud and rocks are calculated and modeled. Major factors causing formation of diapirism/mud volcanism in the South Caspian basin are Pliocene-Quaternary high sedimentation rates (up to 3 km/my), super thick sedimentary cover (up to 25-30 km), predominance of clayey rocks (reaching 80%) in the section, low temperatures (with 15℃-18℃/km gradient), overpressures reaching lithostatic, the onset of petroleum generation lowered to considerable depths. The majority of the mud volcanoes are associated with the petroleum bearing structures. Depths where the liquid, gaseous and solid products of mud volcanoes are sourced appear to be different. The gases have the deepest roots (7-15 km) which are the main force in formation and activity of MVs. Source of the fluidized clayey mass does not lie below 3-4 km. Oils emitted by mud volcanoes are the product of destruction of petroleum accumulations occurring beneath them.

About retardation of a physicochemical processes in overpressured sediments, South-Caspian basin, Azerbaijan

In paper the role of excess pressures in cata- genic processes of the South-Caspian basin (SCB) is considered. The results of the carried out researches taking into account world ex- perience on the given problem allow to con- clude, that SCB (mainly its deep-water part), as well as a number of other basins of the world with overpressures, is characterized by retarda- tion of processes cracking of kerogen and oil, and also reaction of transformation of clay minerals. Periodic intensification of these pro- cesses can provoke development of diapirs and mud volcanoes, which are the centers of pulse unloading of a hydrocarbon products from sys- tem. The conclusion about high prospects of revealing of hydrocarbon accumulations in deep buried deposits in overpressured basins is made.

油气富集域早古生代以来的古地理演化及其对成藏的控制:南美-北非-中东-中亚特提斯域古地理与油气资源

鉴于中国的油气需求与国内外油气资源禀赋,合理有效利用国外油气资源以缓解国内能源需求压力,顺应能源转型与绿色发展趋势,成为国内各类油公司的时代责任与义务。地质研究是油气勘探开发的基础,因此组织了国外油气地质基础研究专栏。为便于读者更好地阅读领悟本期刊发的5篇海外区域研究论文,部分编者撰写了这篇关于5篇海外论文的整体研究背景、各自成果特色及其创新认识相关性的推介。

南里海盆地下库拉凹陷异常高压与油气成藏

南里海盆地是中、新生代发育的弧后裂谷—前陆复合盆地,其中下库拉凹陷具有快速巨厚沉积、异常高压、泥火山发育、低地热梯度的特点。探讨了下库拉凹陷异常高压形成条件、发育特征及其对油气成藏的影响。异常高压的形成主要与该区快速沉积、巨厚塑性沉积、构造挤压、泥火山活动、富含蒙脱石厚层泥岩发育有关,而温热膨胀、烃类生成、黏土矿物脱水对该区异常地层压力的贡献不大。凹陷内2000多米深度已经具有国内罕见的异常高压。由于地层岩性不同,异常高压引起的欠压实在部分构造的泥岩压实曲线和密度曲线上十分明显,而在部分构造中没有反映,并依此把下库拉凹陷中异常高压地层的泥岩压实划分为3种类型。异常高压利于该区储集层物性的保存、油气藏的封闭,控制该区油气分布,促使该区构造和圈闭形成,但也产生了严重的工程难题。

南里海盆地泥火山构造及其对油气成藏的影响

泥火山构造在地震相上为不连续、弱振幅的空白反射或杂乱反射,呈柱状与围岩不整合接触。其分布规律受盆地应力场和构造活动带的控制,在盆地边缘山前冲断带泥火山最发育,盆地中心发育较少,同一构造带上泥火山沿主断层和背斜发育带走向呈串珠状分布。泥火山构造具有幕式活动的特点,并在浅层伴生放射状正断层和塌陷补偿构造。按照泥火山构造成因和构造特征可以划分为背斜型、走滑断层型和逆冲断层型3种。区域地质背景、挤压走滑应力场下的构造活动、快速而具有特色的沉积地层和地层超压环境是该地区泥火山构造形成的主要原因。泥火山构造对油气生成、运移、聚集、保存和破坏以及构造圈闭形成、储集层发育有不同程度的影响。

南里海盆地大油气田的形成条件与分布特征

依据南里海盆地中15个大油气田的资料,应用研究含油气系统的思路与方法,对盆地构造沉积演化及油气地质条件进行剖析,探讨了大油气田的形成条件和分布特征。研究认为,南里海盆地主要发育麦考普组-红层组含油气系统,盆地北缘的大型走滑挤压构造带的油气地质条件最为优越,目前已发现的大油气田集中分布在该构造带上。里海东西两侧岸线附近的褶皱带也具备良好的生储盖条件,有望成为盆地今后油气勘探的有利区带;麦考普组-红层组含油气系统比较年轻,油气的生、运、聚活动仍然活跃,因此,即使是目前勘探程度较高的北缘构造带,仍然具有较大的勘探潜力。