Sanding Production Assessment
Aggressive production strategies, poor hole conditions while drilling, severe depletion and inadequate completion designs can all lead to compressive failure of near wellbore reservoir rock during production. This can give rise to excessive wear and erosion of equipment on the platform and downhole together with significant handling and disposal of dirty sand. In severe cases this can even lead to the abandonment of the well or casing collapse.
Depletion, excessive drawdown, a change in production conditions (well shut-in, water hammer and cross flow), or water breakthrough can all lead to sudden or unexpected sand production. Water hammer can lead to pressure wave transients due to pipeline dynamics being transmitted to the sand face. This can lead to transient increases in the effective stress and consequential increased risk of compressive failure. In a similar fashion the response of differing permeability layers within the reservoir can give rise to transient cross flow pressure gradients between layers. During the period of cross flow the pressure gradient may be sufficiently high to cause mobilization of failed material and cause further destabilisation of the well. Cross flow leading to additional compressive failure can also occur due to inter-well flow where pressure gradients can be set up between different injection wells.
Whichever failure mechanism is responsible, failed material can retain a finite strength and stabilise as ‘sand arches’ due to the frictional resistance within the failed zone. While sand arches can allow sand-free production at higher drawdown than would be predicted by an onset of failure criterion alone they can be disrupted if the frictional resistance is overcome by excessive stress induced failure, while water breakthrough can greatly increase sand production by reducing the capillary pressure between the sand grains.
Ideally detailed laboratory core testing is undertaken for sand production assessments to provide measures of the rock strength. This may include Uniaxial Compressive Tests, Multi and Single Stage Triaxial Tests, Thick-Walled Cylinder (TWC) and Advanced Thick-Walled Cylinder Tests (ATWC). These are fully integrated in our system with preference given to ATWC and TWC tests as these are considered a direct analogue for sanding.
Our sand production assessment is calibrated to sanding and non-sanding incidents from offset wells to help constrain the sanding model where good estimates of depletion and bottom hole flowing pressures are available. Poroelastic effects are fully incorporated in the sanding calculations under coupled depleted far field stress as well as under near field drawdown conditions.
So whether it’s pre-drill risk assessment, or mitigation of a current problem, our Sand Production Assessment will help you maximise the productivity of your resource. Based on your data and calibrated to real observations our sand model will:
- Target core testing programmes to maximise integration with offset log data
- Establish reservoir intervals prone to failure
- Model the effects of planned likely drawdown and depletion to determine critical reservoir pressure
- Determine whether stability may be achieved by alterations of well design
- Provide options and advice for completion strategies
- Estimate the conditions at both the borehole and perforation scale
- Approximate the effects of pressure transients due to well shut-in, water hammer and cross flow on sand face stability
