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Investigation into Laser Perforation of Rock for Petroleum Exploitation
M-Y. LI, B. Han, S-Y. Zhang and Y. Wang

The feasibility of laser perforation on two typical rocks (high strength granite and low strength sandstone) was investigated to develop an alternative drilling technique to overcome the ubiquitous problems in the present mechanical drilling technology. The results showed that for granite and sandstone samples, both laser perforation depth and specific energy increase with prolonging laser irradiating duration. As for granite, the laser perforation induced fracture mechanism was attributed to cleavage, with secondary cracks and numerous regular small platforms on the fracture surfaces. For sandstone samples, clean laser perforated holes consisting of a grey glaze layer and a brown heat affected zone (HAZ) were found, with secondary cracks existing in the inner walls. Meanwhile, obvious cavity and large voids could be easily found in the HAZ, which might be helpful for breaking the cementations and mineral grains. Of significance, laser perforation could lead to reduced mechanical performance of both granite and sandstone; for example, after laser perforation with nine holes, granite and sandstone exhibited compressive strengths of 51.48 and 8.92 MPa, respectively. This is approximately only a quarter of their original values, indicating the feasibility of rock fragment by laser technology.

Keywords: CO2 laser, granite, sandstone, laser drilling, laser perforation, rock fragment, mechanical properties, compressive strength, heat affected zone (HAZ), drillability

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