Keeping Sand Out of the Wellbore
Sand control systems prevent sand from entering the wellbore while allowing the free flow of fluids into or out of the well. Various configurations of sand control include:
- Slotted liners – a series of narrow slots are cut longitudinally in the base pipe
- Wire wrapped screens – wire with a keystone cross section is wrapped around a perforated based pipe with the wire wraps spaced to form a continuous spiral slot around the base pipe
- Wire mesh – sheets of wire mesh, often with multiple layers with different opening sizes designed to trap different sized sand particles are wrapped around a base pipe. Other mesh screens use small mesh cartridges that are pressed into perforations in the base pipe.
- Gravel pack – coarse sand (“gravel”) is pumped into the annulus surrounding the well liner to form a filter to exclude finer sand particles
- Chemical Consolidation – resin is injected into the formation surrounding the well to bind the sand together and stabilize the formation
Threats to Sand Control Systems
Sand control systems can suffer two types of failure:
- Serviceability Failures where the system no longer excludes the intended sand sizes or it impairs the flow of fluid
- Structural Failures where the system deforms by buckling or shear to the point of restricting well access or the casing connections failure
Some common causes of Serviceability Failures include:
- Plugging of openings by fine particles from the reservoir
- Erosion of openings by entrained solids passing through the openings with the fluid
- Deformation of the openings due to strain in the base pipe caused by thermal cycles or formation movement
Some common causes of Structural Failures include:
- Based pipe deformations due to thermal cycles or formation movement
- Hydrogen or hydrogen sulfide exposure causing embrittlement of threaded connections
C-FER Yourself – Helping Improve Sand Control Systems
Testing
- Full-scale structural tests on the base pipe can be used to determine how the sand control element (slot, wire spacing, mesh/cartridge) are affected by axial compression tension or bending.
- Slot width and wire spacing can be measured continuously to show opening/closing behaviour under various loading conditions. If loading is not uniform on the pipe, some openings can get smaller, and others get larger in different regions of the pipe.
- Loading scenarios can consider installation loads such as bending through dogleg or build sections, torsional loading due to rotation while running liners and operational loads such as thermal cycling and formation movements
- Erosion caused by particles entrained in fluid flowing through the sand control system can be used to determine how the sand retention capabilities of the sand control system decline with time
- Threaded connections can be tested to verify that they can withstand the anticipated installation and operational loads. Environmental effects in sour service conditions might also need to be considered in the testing program
Modeling
- Advanced finite element models can be used to assess the impacts of installation and operational loading on the structural integrity of the sand control system and can evaluate changes in the slot opening or wire spacing.
- For thermal wells, time-dependent processes such as creep and stress relaxation should be considered to assess failure mechanisms such low cycle fatigue failure.
Inspection
- Well deformations can be monitored using traditional casing inspection tools with Well Xplore software to visualize deformations.
- Casing inspection tools cannot typically measure sand control openings, but the observed well deformations can be used benchmark structural finite element models that can estimate changes in opening sizes as a function of well deformation.
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Contributor
Brian Wagg, MSc, PEng.
Director, Testing Services
With over 35 years with C-FER, Brian Wagg’s current focus is on applying C-FER’s analytical and full-scale testing capabilities to projects in clean energy including CCUS, hydrogen, geothermal and small modular nuclear reactors.
