Abstract
A new applicable safety factor index (SFI) was developed to identify the impact of mechanical stresses and hydrodynamic forces on the potential sanding of a sandstone reservoir. The SFI is calculated by a fully numerically coupled analysis of the mechanical deformation and hydrocarbon fluid flow in the sandstone formation via FLAC3D software, Itasca Consulting Group, Minneapolis, USA. Sand production is commonly ascribed to mechanical failure while the influence of hydrodynamic forces on sandstone erosion is neglected or underestimated. However, the new SFI enables the designer to quantify the impact of mechanical and hydrodynamic forces separately on the future occurrence of sanding. Quantitative comparison is a beneficial tool to choose the most appropriate layout of the wellbore and perforations. The results demonstrated that hydrodynamic forces may have a more significant effect on sand production than mechanical stresses. Furthermore, the sanding process does not necessarily commence at the wellbore wall and may occur at any spot around the perforations with the highest stress state. The calculated SFI was effectively utilized to reduce the sand production, an intensely problematic issue in the oil field used here as a case study. The new SFI can be deployed to design the optimum wellbore and perforation configuration to decrease the sanding potential in a sandstone formation.
Highlights
For the prediction of sand production, several physical, analytical, and numerical models have been introduced so far
To evaluate the sanding potential of a sandstone formation, it is important to take into account both the hydrodynamic forces and mechanical stresses
Using the new safety factor index (SFI), one can investigate the influence of frequency of shots, the length of perforations, wellbore geometry, and trajectory on the sand production in a sandstone reservoir
Summary
For the prediction of sand production, several physical, analytical, and numerical models have been introduced so far. Most of the models are based on comparing the strength of the rock and the effective stress around wellbore or perforation tunnels. It is assumed that sanding occurs if the strength of the formation is less than the present effective stress under a cycling loading. Reduction of the shear strength during cyclic loading has been investigated through numerous studies [1,2,3]. Morita et al [6] declared that shear and tensile failure can cause instability around perforation tunnels. In Veeken et al [7], triaxial compression and hollow cylinder collapse tests were carried out to investigate the stability of vertical and horizontal boreholes and sanding phenomenon
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