科研之友
微信
新浪微博
Facebook
分享链接
摘要
Maceral (kerogen or organic matter type) and mineralogical composition with the associated porosity of the Upper Cretaceous Eagle Ford Formation, Karnes County, Texas was investigated. In Karnes County, the calcareous mudstone of the Eagle Ford Formation was deposited in an open marine outer shelf to upper slope environment. To adequately characterise all components of this mudrock, a multidisciplinary approach was implemented to analyse 26 core samples from a single producing well that completed within the Eagle Ford Formation. Analyses included organic petrology, organic geochemistry, light and electron microscopy (and spectroscopy), pore size distribution analyses and X-ray diffraction. The bitumen reflectance ranges between 1.94 and 2.08% (calculated VR0 = 1.60-1.69%) indicating the mudrock is in the condensate-rich gas The TOC content ranges between 1.7% and 72% with an average of 3.9%. Mineral composition is dominated in descending order by calcite, clay, quartz and plagioclase. Calcite varies between 32% and 87% with an average of 57%. Porosity measured by helium pycnometry ranges between 3.5 and 10.3% with an average of 7.5%. Organic petrology coupled with backscattered and field emission scanning electron microscopy indicates matrix bitumen as the most significant contributor to the TOC content and porosity. Matrix bitumen contains significant meso- and microporosity and is enhanced by the secondary cracking of the bitumen. An increase in bioclastic (mostly foraminifera) and siliciclastic components correlates with lower TOC content due to the lower volume of organic-rich matrix. Peloids (fecal pellets) are calcareous, organic rich and lack terrigenous sediment indicating a zooplankton source. Pelagic deposition of peloids is interpreted as a primary mechanism of amorphinite deposition which is converted to hydrocarbons and matrix bitumen. The mixed siliciclastic calcareous matrix that surrounds the peloids is comprised of matrix bitumen and dispersed organics from land plants (vitrinite, fusinite and inertodetrinite). The siliciclastic component increases in the middle of the Eagle Ford and marks the boundary (maximum flooding surface) between the lower (TST) and upper (HST) section of the formation. The inorganic and organic components suggest a mixed terrigenous and marine source with both inorganic and organic sediments being derived from the proximal Ouachita thrust belt and from pelagic organisms within the overlying water column. The lower (TST) Eagle Ford Formation contains more micro- and mesopores than the upper (HST) Eagle Ford Formation due to higher TOC content in the lower Eagle Formation. These results illustrate that a multidisciplinary approach is necessary to identify how pore network are distributed within mudrocks and how this distribution is controlled by organic/inorganic deposition and hydrocarbon generation processes.
- 出版日期2017-2-15
