吴起—志丹地区延长组下组合浊沸石的纵向分布特征与成因

吴起-志丹地区延长组下组合包括长8、长9和长10三个油层组。在研究区中、西部，下组合油气主要来源于长7₃烃源岩；在研究区东部，下组合油气主要来源于长9₁烃源岩。624个储层样品的X衍射和薄片镜下观察表明，研究区下组合储层中普遍发育浊沸石胶结物，其体积分数在纵向上具有明显的规律性：研究区中、西部浊沸石体积分数在长8段最低，向下逐渐增高，在长10段普遍发育浊沸石胶结物；研究区东部浊沸石体积分数则在长9₁段最低，向上部长8段逐渐增高，向下部也有所增高，在长10段达到最大值。浊沸石的这种变化规律与烃源岩成熟和流体释放密切相关。浊沸石属于早成岩阶段形成的碱性低温铝硅酸盐矿物，在有机质成熟释放出的有机酸和CO₂作用下，由近及远会发生不同程度的溶蚀作用，造成纵向上距离烃源岩越近，浊沸石残留得越少，距离烃源岩越远，浊沸石保留得越多。该分布规律可以指示烃源岩成熟后释放流体运移的距离和范围。

Vertical Characteristics and Genesis of Laumontite in Lower Combination of Yanchang Group in Wuqi-Zhidan Area

Three reservoir groups are existed in the lower combination of the Yanchang Group in Wuqi-Zhidan area:Chang 8, Chang 9 and Chang 10. In the mid-western part of the study area, the oil and gas mainly originate from the source rocks of Chang 7₃;while in the eastern part of the study area, the oil is from the Chang 9₁ source rocks. The X-ray diffraction and microscope observations of 624 reservoir samples show that laumontite cement is commonly developed in the reservoir in the lower combination. The content of laumontite has obvious vertical regularity:it is the lowest in Chang 8 in the mid-western part of the study area, gradually increases downward,and commonly develops in Chang 10; in the eastern part of the study area, the content of laumontite is the lowest in Chang 9₁, gradually increases in the upper reservoir of Chang 8 and lower Chang 10, and reaches the maximum in Chang 10. This change of laumontite is closely related to the maturity of the organic matter and fluid released from the source rocks. Laumontite belongs to the aluminosilicate mineral formed in the early diagenetic stage under alkaline and low temperature. Under the action of the organic acids and CO₂ released from the mature source rocks, different degrees of laumontite dissolutions occur from near to far. The closer to the source rocks in the vertical direction the formation is, the less the laumontite remains. This distribution regularity indicates the distance and range of hydrocarbon generation and expulsion from source rocks.