A System for Removing and Disposing Of Produced Sand
Authors: Garcia Juan A. 
Published: December 2007

A common problem associated with oil operations along the Gulf Coast is the production of sand. The problem is particularly acute in the prolific oil production of sand. The problem is particularly acute in the prolific oil fields of Offshore Louisiana, where the solids, when finally removed, are difficult to dispose of within existing antipollution laws. Here is the system developed by one company for removing and disposing of sand while satisfying government standards.

Introduction

Costly problems associated with the handling and transporting of produced solids on offshore production platforms and in pipelines leading to shore production platforms and in pipelines leading to shore facilities caused Exxon Company, U.S.A., to start an active program to develop a system for offshore disposal of sand within regulatory standards. Laboratory tests proved the effectiveness of centrifugal agitation of produced sand in the presence of a surfactant in water for removing all measurable traces of oil. A pilot unit using the principle was designed and pilot unit using the principle was designed and installed on an offshore platform to test the reliability of such a system operating under field conditions. Modification resulting from pilot test studies were incorporated into a design for a new, more reliable, less complicated permanent system. The new system was installed on the Grand Isle Block 16 L platform and on West Delta 73 A-D production complex. Both systems have been monitored for quality of discharge, and results have shown no trace of oil on the sand samples.

Description of System

Fig. 1 is a schematic diagram of the entire sand-handling system currently in operation. The system can be divided into three basic parts: the sand removal system, the sand transporting system, and the sand cleaning and disposal system.Sand is separated from produced fluids by conventional cyclones shown as in Fig. 1. The fluids are discharged into a surge tank, where a transfer pump moves fluid through pipelines to shore pump moves fluid through pipelines to shore facilities. Separated sand is collected in silt pots below each cyclone. (The pots are emptied into a collection trough on an adjustable, timed cycle.) Sand is forced out of the pots by differential pressure since the pots are maintained at pressures exceeding those of the collection trough. Sand is moved from the collection trough by water continuously supplied by a centrifugal pump. Sand, water, and oil move into the classifier vessel where sand falls to the bottom of the cone and free oil gravity separates to the surface for removal. The vessel pressure is controlled by an adjustable regulator that vents gas to a surge tank. A water-level control actuates a dump valve, which maintains the vessel water level as shown. An oil-level control actuates a dump valve, which empties oil to the surge tank. Water and sand move from the classifier as the dump valve opens. The stream enters the No. 1 cyclone of the sand washer. Sand is discharged into the sand washer, and the water and free oil move into the separation vessel via the cyclone overflow line. (Fig. 2 is a larger-scale schematic.) Water and oil are allowed to gravity-separate in this vessel. Water is taken from the bottom of the separation vessel to supply the recirculation pump, completing the closed loop. Water can enter and leave this loop only at the cyclone banks and at the No. 1 cyclone, respectively.

JPT

P. 450