The normal producing situation is that a well may “make” a rather uniform amount of sand or “fines” independent of production rate until some critical production rate is exceeded. Continued production above the critical rate results in increasing amounts of sand production.
Sand grains are stabilized by compressive forces due to the weight of the overburden, by capillary forces, and by cementation between sand grains. Causes of sand production are related to:
1. Drag forces of flowing fluid which increase with higher flow rates and higher fluid viscosity.
2. Reduction in formation “strength”often associated with water production due to dissolving of cementing materials, or a reduction in capillary forces with increasing water saturation.
3. Reduced relatives permeability to oil, due to increased saturation, which increases pressure drawdown for a given oil producing rate.
4. Declining reservoir pressure which increases compaction forces and may disturb cementation between grains.
Basically sand production can be controlled by three mechanisms:
1. Reducing drag forces. This is often the cheapest and most effective. It should be considered along with any other method of control. It is often the natural outcome of proper well completion practices.
2. Bridging sand mechanically. This is the “old standby”and properly done has wide application. It is more difficult to apply in multiple zones or small diameters.
3. Increasing formation strength. Sand consolidation has specialized application, it leaves a full-open well bore and can be used in small diameter casing.