Reclaiming Produced Water For Steam Generation In The Kern River Field
Authors: Carrell Michael A. 
Published: December 2007

Water produced with crude oil can successfully be reclaimed for use as oilfield steam generator feed-water. Getty Oil Company in the Kern River Field near Bakersfield, California, reclaims and clarifies 80,000 cubic meters of produced water per day for use as steam generator feedwater.

Introduction

Getty Oil Company in the Kern River Field employs tertiary thermal steam flooding methods to produce 13 degrees API gravity crude from depths of 300 meters. Approximately 230 oilfield steam generators consisting of 6 and 15 megawatt models are used to provide steam for this operation. Feedwater demand is 80,000 cubic meters per day and is expected to increase another 30 percent when the field is fully expanded. percent when the field is fully expanded. Because of the arid climate of Bakersfield, California, the most available and economical source of steam generator feedwater is the fresh water which is produced with the crude oil. Recycling the produced water also minimizes disposal problems. For produced water also minimizes disposal problems. For each cubic meter of oil, nine cubic meters of water are produced. However, before this produced water can be used for feedwater, the residual oil, suspended solids and hardness must be removed. Getty Oil Company in the Kern River Field has designed and built a reclamation facility for this purpose.

PROCESS DESCRIPTION AND THEORY PROCESS DESCRIPTION AND THEORY The facility employs chemical treating, mechanically induced and dissolved gas flotation, sedimentation, and pressure cake filtration to remove suspended solids and oil in the produced water. Following these processes, sodium zeolite cation exchange softeners are used to remove hardness. A process line diagram is shown in Figure 1.

Reclamation of the produced water begins after initial gravity oil-water separation has reduced insoluble oil and suspended solids to approximately 200 milligrams per kilogram each. Table 1 presents water analyses of the produced water before and after the reclamation process. The first process utilizes an oilfield depurator unit which mechanically induces flotation air to reduce oil and suspended solids to 20 and 100 milligrams per kilogram, respectively. Mechanically induced air flotation is accomplished in the depurator unit using a motor-driven rotor mechanism which pulls air or gas into a cell with the produced water. The resulting shearing forces cause the produced water. The resulting shearing forces cause the gas to form minute bubbles which attach to oil particles and suspended solids as they rise to the particles and suspended solids as they rise to the surface. A dense froth is formed on the surface and the oil and solids are removed from the cell by skimmer paddles. paddles. Following the depurator units, the produced water flows through a 122 centimeter pipeline to sedimentation basins where chemical treating with reverse emulsion breakers and polymer coagulants are added to break out and agglomerate oil. Some of the suspended solids also drop out during the sedimentation period. Produced water discharged from these basins then Produced water discharged from these basins then contains 10 milligrams per kilogram insoluble oil and 80 milligrams per kilogram suspended solids. These basins also provide important surge capacity as the inlet produced water volume can vary over 16,000 cubic meters produced water volume can vary over 16,000 cubic meters of water per day.

The discharge of the sedimentation basins to the physical plant inlet is through a 91-centimeter line physical plant inlet is through a 91-centimeter line to pumps which charge dissolved gas flotation cells. Nitrogen gas is introduced into the produced water stream through eductors on the cell charge pumps. The nitrogen is stored as a liquid at a nearby site and is vaporized and automatically supplied to the plant upon demand. The nitrogen dissolves into plant upon demand. The nitrogen dissolves into minute bubbles which then contact oil particles and suspended solids. The oil and solids are lifted to the surface in the flotation cells and are skimmed off. This process reduces insoluble oil and suspended solids to 5 and 50 milligrams per kilogram, respectively. The cells then discharge to a holding tank prior to the filtering process.