TABLE OF CONTENTS Leon Robinson
Exxon, retired
Drilling fluid enters the removal-tank section after it passes through the main shale shaker. Immediately below the main shaker is the first pit, called a settling pit or sand trap. Fluid passing through the shaker screen flows directly into this small compartment. The fluid in this compartment is not agitated. This allows solids to settle. The fluid overflows from the sand trap into the next compartment, which should be the degasser suction pit. The sand trap is the only compartment not agitated in the mud tank system.
The sides of a sand trap should slope at 45 or more to a small area in front of a quick opening discharge valve. When the solids are dumped, the valve can be closed quickly when drilling fluid begins to flow from the trap. The purpose of the quick-opening valve is to allow only settled solids to leave the compartment, with minimal loss of drilling fluid. In many cases during periods of fast drilling, with coarse or damaged shaker screens in use, the sand trap will fill several times per day.
An effective sand trap requires an overflow weir of maximum length to create a liquid column as deep as possible. A common, and recommended, practice is to utilize the full length of the partition between the sand trap and the degasser suction pit.
The rate at which solids settle depends on the force causing the settling, the dimensions of the solid, and the fluid...
