Tor Erling Unander

Constitutive testing of Red Wildmoor sandstone

The first objective of this research was to improve the experimental measurements for the constitutive behaviour of Red Wildmoor sandstone by optimizing the boundary conditions and specimen geometry, and improving the triaxial test instrumentation. The uniformity of deformation of the rock specimen was improved by minimizing specimen bulging due to specimen slenderness and end-surface frictional constraints. The improvements in the instrumentation were aimed at improving the monitoring of the applied forces, axial and radial deformations, and macroscopic rock failure through use of high precision LVDTs and cantilever gauges, acoustic emission measurements and acoustic pulse transmission velocities. The second objective was to obtain test data for the constitutive modelling and calibration of Red Wildmoor sandstone under various saturating conditions and saturation fluids. An additional task was an experi mental study for the improvement of the uniaxial compression test as an index text for rock mechanics applications. The performed modifications allowed the reliable collection of post-peak stress test data of material softening behaviour, and the identification of the point of macroscopic failure of the specimen beyond which the test data cannot be used directly for continuum modelling of material behaviour.

Flow geometry effects on sand production from an oil producing perforation cavity

Abstract Physical model experiments have been performed on perforation cavities in a weak sandstone. The objective of the study has been to investigate the effect of the flow geometry on sand production risk. Two extreme geometries have been tested, one with flow mainly axially towards the tip of the cavity and one with fluid flowing radially towards the side of the cavity. The experiments have been performed in a special pressure vessel for sand production studies. We have recorded the deformation of the cavity, the flow rate through the sample and monitored sand production and acoustic emission activity as functions of the imposed confining pressure and pore pressure drop across the sample. From the tests, we have found initial cavity failure and initial sand production at various combination of confining and pore pressure. The results have also been corroborated by finite element simulations. We have concluded that by directing the flow through the bottom of the cavity sand production is inhibited compared to the case where flow mainly enters through the side of the cavity. This is because the cavity fails along the wall first, while the bottom is intact. As flow promotes the removal of failed material, radial flow increases the risk of sand production.