Studies of Kerogen From Baise Basin,Guangxi-Also on Relationship of Evolution of Kerogen and Clay Minerals

Kerogen is the direct original material of oil-forming. To determine the type and the mature degree of kerogen is one of the important work in petroleum geology. While studing the clay minerals of Baise Basin,Guangxi,the authors made some detialed work on the kerogen of this oil-forming region. The type,mature degree,and the evolution process of kerogen was determined through X-ray diffraction and micro-region analysis method,and also by microscopic,atom distribution and infrared work. According to the results of X-ray analysis, the aliphatic degree (Fa) of the kerogen in this region is 0. 28 to 0. 37. On increasing of the depth in the same geological section,the Fa becomes higher, that is, the kerogen evoluted to mature. By calculation, the height of aliphatic nuclei (Lc) is between 16. 60 and 20. 76 A,the layer number (n) of them is 5 to 6. These are the characteristics of type III kerogen. The evolution process of the kerogen in this region was studied using micro-region method,and also using some routine methods. The lower matured kerogen was photoed by microscope, and the distribution of the atoms in it was analyzed by electronic probe. It is shown that the carbon atom in this kind of lower mature kerogen is not homogeneous,normally higher in the center,lower in the outer part. Iron and silica are also concentrated to the center. Most of the Kerogen have FeS2 nuclei,and around the nuclei mainly are clay minerals. The evolution trent of the mature degree of the kerogen is consistent with the evolution trend of the clay minerals,that is,montmorillonite evoluted to illite/montmorillonite. The combining patterns of organic molecules and clay minerals were also discussed. According to the thermodynamics data and some experiments of transforming clay minerals, we qualitatively calculated the water and heat that produced by the montmorillonite to illite. It will let out 30 to 40 grams of water and 100 kcal of heat by 1 mol montmorillonite transform to illite. This may be the medium and dynamic power source of the forming,evolution,and decomposition of kerogen. It is concluded that the clay minerals were the catalytic promoter for organic material evelute to hydrocarbon.