Texture development of mesophase in reservoir pyrobitumen and the temperature-pressure converting of the gas reservoir in the Chuanzhong Uplift, Southwestern China

The Neoproterozoic-Lower Paleozoic dolostone gas reservoirs in the Chuanzhong Uplift in Southwestern China contain the mesophase pyrobitumen (pyrobitumen with mesophase). The mesophase in the pyrobitumen is mostly composed of a mixture of condensed macromolecule polycyclic aromatic hydrocarbons (PAH), and has been mostly converted to various grain, flow, and domain textures. The volcanic activity nearby the Chuanzhong Uplift may have generated very hot (over 300 °C) hydrothermal fluid, with migration of the fluid into the dolostone reservoir transforming the hydrocarbons in the reservoir into an anisotropic carbon by-product, which formed under high temperature and pressure conditions;over 300 °C and 200 MPa according to fluid inclusion analysis. The high temperature-pressure in reservoir was caused by sudden devolatilization of the hydrocarbons due to hydrothermal heating, which formed the unusual texture of the mesophase. The elliptical mesophase grains (EG), the honeycomb structure of pyrobitumen, and the occurrence of polarized classes of mesophase in single pyrobitumen deposits are all unusual textures. This study investigates the texture development of this pressure-affected pyrobitumen. Observation and study of the mesophase suggest that the class of mesophase in pyrobitumen is determined by temperature, while pressure (assessed from associated fluid inclusions) significantly affected the texture. Analysis of the texture of the pyrobitumen in conjunction with previous thermometry results from methane inclusions suggests that the high class mesophase of the pyrobitumen could be applied as a temperature indicator for geological conditions. Furthermore, the unusual textures of the pyrobitumen including elliptical mesophase grains (EG), the honeycomb structure of pyrobitumen, and the occurrence of polarized classes of mesophase in single pyrobitumen could reflect the abnormal high formation pressure.

川中隆起安岳气田古油藏成藏时间厘定

安岳气田是中国目前最大的古老和深层气田,由新元古代-早古生代地层中的古油藏经原位裂解形成。由于古油藏-裂解气藏演化程度较高、时代较老,对其成藏演化的研究,特别是古油藏成藏时间的厘定,长期以来存在较多争议,缺乏足够地球化学证据的佐证。通过最新的实测大地热流史和类似地区的烃源层生烃门限研究,利用地质类比法替代流体包裹体测温,重建关键井埋藏史-热史,厘定德阳-资阳裂陷筇竹寺组烃源层的生烃和古油藏形成和破坏的时间,分析了古油藏的演化过程。地球化学实验和相关地质分析表明,筇竹寺组烃源层生烃时间既古油藏成藏时间约为275~263 Ma,相当于早二叠世后期(孔古阶)-晚二叠世。之后的深埋使古油藏自三叠纪初期开始裂解,在中侏罗世末期-早白垩世初期古油藏被完全破坏并形成大型裂解气藏。

四川盆地柏垭——石龙场地区自流井组大安寨段油气成藏地质条件

从大安寨段油气组分和物性分布所反映的烃类运移 ,结合中、上侏罗统的展布 ,提出川 30井和川 43井区存在一个燕山期隆起和油气富集带。在其后的漫长岁月中 ,该带储集层因深埋而致密化 ,油气被“冰冻”于储集层中。喜马拉雅期构造运动 ,改造、支解了古隆起 ,形成了若干背斜与鼻状构造 ,这些正向构造上裂缝发育 ,改造了其储集层的储渗条件 ,停滞的油气具有了工业产能。因此 ,大安寨段的油气是燕山构造运动期富集。

普光和川中地区特大型气田颗粒滩储层特征类比及启示

为揭示四川盆地特大型碳酸盐岩颗粒滩相储层特点及差异性,为类似地区的油气勘探提供参考,以四川盆地普光地区和川中古隆起2个特大型气田碳酸盐岩颗粒滩储层为研究对象,对两个地区颗粒滩沉积储层基本特征及储层主控因素进行综合类比研究。研究揭示,两个地区颗粒滩储层具有共性特点,均处于高能沉积相带,具有明显的早期沉积环境和构造演化的继承性,储层具有明显的准同生期暴露溶蚀、强云化和早期油气充注等特点。两个地区储层又具有一定差异性,普光地区与陆地隔离,具有明显的加积特征,形成厚度大且集中分布的带状鲕粒滩区;川中古隆起区则与陆地相连,颗粒滩具有明显迁移结构,面积大,但厚度相对较小。研究认为,颗粒滩沉积是大型储层形成的重要物质基础,沉积结构对其控制明显;准同生期暴露溶蚀、强白云石化作用和早期油气充注及后期裂解是两个地区现今优质白云岩储层得以形成和保存的核心因素,优质的成藏要素组合为优质的云化颗粒滩储层的形成和保存提供了有利的时空系统条件。

从“四古”特征论四川盆地川中古隆起北斜坡龙王庙组天然气勘探潜力

近年来,四川盆地川中古隆起轴部发现了安岳特大型气田,主要目的层为震旦系灯影组、寒武系龙王庙组。但对古隆起斜坡区的成藏问题探讨较少,直接制约了油气勘探突破和发现。基于野外、钻井岩心和地球物理资料分析,重点论述川中古隆起北斜坡龙王庙组“四古”(古颗粒滩体、古老烃源岩、古圈闭和古构造)对成藏控制作用,并对勘探潜力进行评价。研究表明:①北斜坡龙王庙组沉积期颗粒滩体叠置发育,为准同生期岩溶作用形成粒间孔、粒内孔等类型储集空间形成提供物质基础;②北斜坡紧邻德阳—安岳裂陷,下寒武统筇竹寺组优质烃源岩为天然气聚集提供了充足的气源;③斜坡构造背景下发育的岩性—地层和岩性—构造复合类古圈闭为油气聚集提供有效聚集空间;④古构造多期活动和调整控制油气成藏演化;⑤川中古隆起北斜坡龙王庙组油气成藏条件优越,勘探取得突破的关键在于寻找活动强度较弱的断层附近的岩性—地层和岩性—构造圈闭。不同类型天然气藏发育有利分布区总面积达3652km2,资源量大,勘探前景广阔。