Volcanic Rock Fracture Distribution And Controlling Factors

Volcanic rock reservoirs have poor physical properties and strong heterogeneity.Macroscopic fractures play an important role in improving reservoir percolationcapability and increasing the reservoir space, so the study of macroscopic fracturedistribution is of great significance. According to the borehole wall imaging loggingdata, the volcanic rock fracture in the Yingcheng formation of the Xujiaweizi faultdepression has zonal distribution, with many periods of time, plane outspreadconcentrated in the direction of several advantages, account for the vast majority ofnearly east-west and nearly south-north（including conjugate joints with nearlysouth-north distribution）, followed by NNE, SSW, NNW and SSE. With regularity onlongitudinal, starting point is a uncompormity surface or a big eruption intermittent,with the increase of depth, fracture porosity decreases gradually. Generally near theunconformity surface, karst mesh fracture or high Angle fracture development,forming high corrosion fracture porosity. Tectonic seam down relative developmentsection, fracture porosity absolute value is smaller, with the increase of depth, fractureporosity absolute value reduced. Local section due to primary seam cracks and thelate tectonic superimposition, cause local increase fracture porosity, cracks formed adevelopmental cycle. Caused by volcanic eruption superposition of multiple cycle, theperiod of fracture distribution of heterogeneity of volcanic rocks, the formation ofcracks on the vertical cyclicity, development degree of unconformity surface orweathering surface as a boundary.Volcanic rock type, formation, eruption form and tectonic position are the staticcontrol factors of the fracture, and the foundation of the fracture formation, Its controlof the dynamic factors (such as tectonics, weathering dissolution) response,determines the distribution of cracks in different periods. The control factors of thevolcanic rock fracture development mainly include the control action of volcanicfacies belt, the structure of the fracture development in the area and volcanic rocklithology. Around the crater, fracture development very well in eruption faciesvolcanic breccia and volcanic agglomerate. The condensing shrinkage joint developswell in the volcanic rock bottom of the overflow facies. In the development of thevolcanic facies zone, this kind of fracture develops well that due to the upward forcewhen the magma eruption and Magmatic explosive force caused by gas liquidexplosive effect.