氟碳钙铈矿中6R和3R多型微双晶结构的透射电镜研究

采用透射电镜技术,对产于我国西南地区的钙稀土氟碳酸盐矿物出现的微结构特征进行了研究。发现氟碳钙铈矿6R和3R两种多型均存在微双晶结构。电子衍射分析和晶格像观察表明,既使在微区范围,氟碳钙铈矿也多以混层晶、多型和微体双晶等衍生体产出。6R和3R多型微双晶共格连生,与主衍射体6R多型共存于一种自然晶粒,它们均以间距为1.40nm的单元层组成氟碳钙铈矿“多晶”。6R和3R多型组成的双晶类型相同,属(0001)为双晶面的面律(旋转)双晶。     

Geochemistry and origin of sour gas accumulations in the northeastern Sichuan Basin, SW China

Significant natural gas reserves have recently been discovered in the Lower Triassic oolitic reservoirs from northeastern Sichuan Basin, SW China. In the wake of the December 2003 sour gas well blow-out, this study presents an overview on the petroleum geology and geochemistry of the sour gas accumulations in the study area. Two types of natural gas accumulations were identified in the Lower Triassic oolitic reservoirs, both containing highly mature thermogenic gases, with their hydrocarbon source rocks in Upper Permian strata. Natural gases from the area south of the ancient Kaijiang-Liangping Seaway are generally sweet gases formed as the result of thermal maturation, whereas those discovered from north of the Seaway are products of both thermal maturation and thermochemical sulfate reduction of early accumulated oils in the Feixianguan Formation reservoirs. The proposed origins of the gases are supported by their chemical and stable carbon isotope compositions, as well as the presence or absence of pyrobitumens in the reservoir. The distribution of gas accumulations is controlled predominantly by the combination of lithologic and structural factors. The regional variation in the concentrations of H₂S in the gases appears related to the presence and thickness of anhydrite-bearing evaporitic rocks interbedded or intercalated with the oolitic reservoirs.