高拘束圧下の砂中ケーシング周面摩擦力に及ぼす表面粗さの影響*

Abstract

In this study, friction tests were conducted on simulating casing in the sand under high confining pressure in order to clarify frictional properties of the casing compose production well and formation which are prepared for methane hydrate development. Three types of simulated casing (maximum roughness Rz=2.7, 14.7, 30.0) and Toyoura sand (mean particle size D50=200μm), No.8 silica sand (D50=90μm) were used for the specimens. Simulating casing was produced based on the surface roughness of actual casing. During the friction tests, effective confining pressure was increased step by step from 0.2 MPa to 3.0 MPa and frictional strength was measured in each step. As the results, relation curve between friction and casing displacement changes from hardening behavior to softening behavior as effective confining pressure increases. In addition, effective secant friction angle decreases with effective confining pressure increase for high roughness specimen instead of increase with effective confining pressure increase for low roughness specimen. Friction between casing and sand under high confining pressure is dependent on effective confining pressure and the ratio of mean particle size of sand surface to surface roughness of casing. Finally, an estimated formula for frictional strength using effective confining pressure, mean particle size and surface roughness was proposed which can express experimental results well.