Thermodynamic Calculations of the Laumontite Dissolution and Prediction ofSecondary Porosity Zones: A case study of horizon of Xujiaweizi Fault Depression
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摘要: 浊沸石是徐家围子断陷深层砂砾岩中广泛分布的一种胶结物，被有机酸溶蚀后，形成大量次生孔隙，为油气的聚集提供了储集空间。为了预测深层次生孔隙发育带的分布，本研究应用热力学计算方法，定量讨论了徐家围子断陷深层营城组砂砾岩中浊沸石的溶解—沉淀过程和次生孔隙的形成机理，并提出了溶解—沉淀指数DPI的计算模型,定量表征溶蚀作用的强度。通过叠合DPI等值线图和沉积相图，预测了浊沸石溶蚀形成次生孔隙发育带的分布。结果表明，次生孔隙发育带主要分布于DPI>2.5的扇三角洲前缘和辫状河三角洲前缘砂砾岩体中。Abstract: Laumontites are important and widespread cements formed in middlelate diagenetic stage in the deepburied glutenites of Xujiaweizi Fault Depression，Songliao Basin. They are later dissolved by organic acids released from kerogens during hydrocarbon generation and expulsion，forming secondary porosities. The secondary porosities within deeply buried glutenites are the main reservoir space of hydrocarbons in the deep formation of Xujiaweizi Fault Depression. In order to predict the distribution of secondary porosity zones，the dissolveprecipitation states of the laumontites and the forming mechanism of secondary porosities in the reservoirs of Yingcheng Formation were studied by using thermodynamic method. Dissolutionprecipitation index DPI was proposed to quantify the dissolution and precipitation of laumontites. The distributions of the secondary porosity zones were predicted by overlapping the DPI contour map over the sedimentary facies map. As the result shows，the secondary porosity zones mainly distributed in the fan delta front or braided fluvial river delta front glutenites，where DPI is greater than 2.5.
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