In non-compliant sand control completions such as stand-alone-screens, the annular gap between the wellbore wall and the screen has always been considered detrimental to efficient inflow. They are typically associated with large skins resulting from the mixing of failed sand grains and the development of a new and continuously changing permeability as the collapsing material starts to compact onto the screen. Annular movement of sand grains and non-uniform bridging creating "hot" spots will eventually lead to erosion and completion failure. Previous researchers have investigated the change in permeability of failed rock into annular gaps generated in non-compliant sand control completions and identified that packed material in this space can result in severe distortion to flow patterns and restrictions.
This paper describes the mechanical and flow process occurring as the wellbore wall collapses onto the screen surface. Constitutive models are used to characterise the mechanical behaviour of the failed material in terms of deformation and collapse of the near wellbore onto the screen. Continuous (foot-by-foot) inflow models are presented to illustrate the impact of the deformation process as the annular gap is filled up on inflow. A detailed laboratory testing program and its results are presented to validate both processes using samples from North Sea sandstone reservoirs. The results indicate that for non-compliant sandface completions such as stand-alone screens, it is possible to determine whether the collapse of the wellbore will occur and how productivity will be affected. From the mechanical point of view the rock follows an extension-dilatancy-compaction path. This will at the same time produce a varying permeability and hence inflow, the magnitude of which will depend on factors such as pore pressure, drawdown pressures, reservoir rock mechanical properties and mineral composition. This extensive testing program has led to the development of a series of analytical models, testing procedures and design methodologies for wells being completed with non-compliant sand control completions.