Abstract:

Characteristics of fracture development in the 2nd member of the Upper Triassic Xujiahe Fm in Xinchang gas field were analyzed through outcrop observation, logging curve, image logging and analysis of borehole cores.The fractures in the studied interval are dominated by low angle fractures, followed by oblique fractures, high angle fractures and map cracking.And the strikes are mainly NEE, NE and SEE.The fractures can be divided into tectonic shear cracks, structural tensile fractures and bedding cleavages according to their genesis.On the basis of these studies, a three-dimensional numerical model of tectonic evolution was built according to the basic geological data and tectonic evolution features.Criteria for fracture identification were established based on theories of structural geology and taking the core observation and well logging analysis, laboratory test results into account.The calculation result shows that the T²⁽²⁾x, T²⁽⁴⁾x and T²⁽⁷⁾x sandstone roof fractures mainly developed near the fault zone.In the wing steep turn and structure peak area are main low angle shear fractures.And many tensile fractures are developed in the structure highs.Research results are basically consistent with exploration results, so the conclusion has a certain practical application and reference value.

Key words: fracture prediction, fracture characteristics of sandstone, second member of the Upper Triassic Xujiahe Formation, Xinchang gasfield, Western Sichuan Depression