The Experiment Of Compression, Rebound And Fracturing Of Sandstone And Mudstone And Preliminary Analysis On Origin Of Cracks

In this dissertation, the author studies on the difference of the compression coefficient and rebound coefficient between sandstone and the mudstone, by the Compression-Rebound experiment, the fracturing characters of sedimental rock with different structure, based on fracturing experiment, and the cracks of sandstone, mudstone and their interface, using core and thin section, in the the Upper Paleozoic of Ordos Basin. Based on the above, the author also studies on the relationship between cracks and gas bearing of sandstone, with logging materals. The conclusions are as follows:1. Under the same pressure, there are some differences between the Compression strain and the Buck rebound strain in the parallel and vertical dimension of the crude sandstone, middle sandstone, Fine sandstone and the mudstone. The general order of high to low is: crude sandstone>middle sandstone>Fine sandstone> mudstone.2. Under the same stress conditions, there are Bursting Strength differences between the parallel and vertical dimension of the rock: the rock with the strong heterogeneity of rock structure in the direction of perpendicular to the level, has the lower rupture strength in the direction of parallel to the level than the direction of vertical to the level, and it's easy to produce cracks in the parallel dimension; And the rock with the strong homogeneity of rock structure in the direction of perpendicular to the level, has the lower rupture strength in the direction of vertical to the level than the direction of parallel to the level, and it's easy to produce vertical level joint.3. During the process of Vertical subsidence and lateral extrusion shrinkage in the Ordos Basin, the rocks of small shrinkage in the direction of parallel to levels is priority to break, and the rock with the strong heterogeneity of rock structure in the direction of perpendicular to the level is easy to form cracks in the parallel dimension; the rock with the strong homogeneity of rock structure in the direction of perpendicular to the level is easy to form cracks in the vertical dimension. In addition, during the procession of decompression and stretching caused by the uneven erosion or rupture, the elongation of different lithology is different, and can further formed parallel level joint, and generate joint slip.4. According to the observation of rock core and slice, we can find that it generally developed parallel level joint in the interface of sandstone and mudstone in Upper Paleozoic in the Ordos basin. These cracks could be effective communication of sandstone and mudstone, and expand the sandstone reservoir range. The statistics showed that there would be 35.17% in the sandstone and mudstone interface and 17.32% in the mudstone of 381 high value hydrocarbon measured by gas of Shan 1 and He 8 Member in Upper Paleozoic in Ordos basin, which indicates the impact on gas reservoir range of the cracks in sandstone and mudstone interface and mudstone.