The Replacement of Hydrocarbon Diluent With Surfactant and Water for the Production of Heavy, Viscous Crude Oil
Authors: McClaflin Gifford G. , Clark Charles R. , Sifferman Thomas R. 
Published: December 2007

Viscous crudes often are produced by means of a low-viscosity hydrocarbon diluent to decrease viscosity of the produced fluid in the tubing and the flowlines. Rod-pump difficulties may result from the slow fall of the rod string caused by high fluid viscosity. The use of a diluent reduces these rod-fall and associated flow problems.

Our goal was to replace the diluent completely with a water/surfactant system without increasing the flowline pressures. This was accomplished with a produced water/surfactant mixture, However, in one field we found that using a combination of diluent, surfactant, and water was the most economical way to produce the crude. The crude is dispersed in a water-external system so that the viscosity is decreased appreciably.

We initially evaluated different chemicals in the laboratory. Later tests were on individual wells, a 6-well pilot, and finally a I5-well pilot. Economics of the new system are projected to be more favorable than those of using diluent alone.

This system can be used not only for heavy crudes but also for waxy crudes that have high pour points and are thus difficult to produce. It allows a lower pumping cost because of reduced viscous drag and can be more economical than some diluent systems.

Introduction

Our previous work1 described various techniques for reducing the viscosity of waxy crudes that are also applicable to heavy crudes. In addition to the preparation of oil and water emulsions, these techniques included:dilution with lighter oil,preheating with subsequent heating in the line,preheating and insulating, andinjection of water to form a water ring.

McAuliffe describes oil-in-water emulsions.2,3 We also have received patents in this area.4–8

The production of heavy, viscous crude at Cat Canyon field near Santa Maria, CA, requires the use of a viscosity reducer that allows the crude to be pumped from the wellbore to storage. Kerosene distillate (KD) has been used for this purpose at Cat Canyon for some time. However, cost and availability of KD at Cat Canyon caused some concern, so we began a research program to find an alternate to the KD mode of production.

Our goal was to reduce viscosity of the heavy crude by some way other than dilution with a hydrocarbon solvent. By producing an oil-in-water emulsion, we succeeded in reducing the viscosity of the heavy crude oil from ~3,000 cp at 170 to 200°F to only 50 to 100 cp at these temperatures. We produced the oil-in-water emulsions by mixing the oil with water that contained an emulsifier.

Another part of our objective was to produce a reversible oil-in-water emulsion that, after being prepared at the well, would have just enough stability to reach the heater-treater before separating into an oil layer and a water layer. In other words, we wanted to produce an emulsion that was not too stable; otherwise, it could cause problems at the heater-treater.

The initial laboratory phase consisted of screening 44 commercial oilfield emulsifier-type chemicals to find a product that would form a low-viscosity. oil-in-water emulsion when used with the viscous Cat Canyon crude. Commercial Surfactant A. which gave the best results in the laboratory, also gave the best results in field tests conducted at Cat Canyon. The commercial product was more economical than KD alone, but we wanted the least expensive product. Therefore, it appeared more economically attractive for us to develop our own emulsifier packages.

The work covered in the first part of this paper was conducted in wells at Cat Canyon field, first with commercial oilfield emulsifying-type chemicals and second with emulsifier packages developed in our laboratory.