Thermodynamic Calculations of the Laumontite Dissolution and Prediction ofSecondary Porosity Zones: A case study of horizon of  Xujiaweizi Fault Depression

Key words: 
• tight glutenite /
• unconventional reservoir /
• laumontite /
• deep formation /
• secondary porosity zone /
• Xujiaweizi Fault Depression /
• Songliao Basin

Abstract: Laumontites are important and widespread cements formed in middlelate diagenetic stage in the deepburied 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 dissolveprecipitation states of the laumontites and the forming mechanism of secondary porosities in the reservoirs of Yingcheng Formation were studied by using thermodynamic method. Dissolutionprecipitation 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.