Steam Distillation Drive-Brea Field, California
Authors: Volek C.W. , Pryor J.A. 
Published: December 2007

This process has been field tested in a steeply dipping reservoir containing 24 degrees API oil at a depth of 4,600 feet. The very stable steam drive showed little tendency for early heat breakthrough to downdip wells. Residual oil saturations of 8 percent were achieved and the produced oil gravity was increased by light components distilled from the produced oil gravity was increased by light components distilled from the oil remaining in the steam zone.

Introduction

Most thermal recovery methods have been applied in high-viscosity reservoirs with the objective of increasing, oil production by reducing oil viscosity. The primary objective of a steam distillation drive is not to reduce oil viscosity but to reduce the residual oil saturation below that obtainable by ordinary waterflooding.

In addition to its improved displacement efficiency, steam drive yields high sweep efficiency when steam is injected updip in steeply dipping sands. The objective of the Brea steam drive was to test the feasibility of driving a relatively light (24 degrees API), low-viscosity (6 cp), volatile oil from updip injectors to down structure producers.

Process Process In reservoirs containing volatile oils, very low residual oil can be obtained by a combination of steam displacement and steam distillation. In a steam distillation process (see Fig. 1), hydrocarbons are more readily vaporized because of a lowering of their partial pressures in the presence of steam vapor. partial pressures in the presence of steam vapor. The light components are distilled from the residual oil and transported to the steam front where they recondense and mix with the oil bank to form a solvent slug. As the steam zone advances, this solvent slug. is displaced and redistilled to further increase oil recovery. Residual oil saturations below those obtainable by steam driving nondistillable oils are possible. Other mechanisms attendant with this process possible. Other mechanisms attendant with this process that account for the recovery of additional oil beyond what is possible with waterflooding are:

reduction in oil viscosity, which improves oil mobility; thermal expansion of the oil; and gas drive from the steam vapor phase.

In addition to in capacity to reduce oil saturation, steam driving is a relatively stable displacement process in light oil reservoirs (i.e., little oil is process in light oil reservoirs (i.e., little oil is by-passed). This stability is enhanced by both fluid convection and thermal conduction effects. The first stabilizing influence is the higher volumetric vapor flow rates in the steam zone compared with the liquid flow rates ahead of the steam front. Application of Darcy's law to both sides of the condensation zone in a situation where the pressures are generally less than 1,000 psi and the oil has a low viscosity shows that the pressure gradient is higher on the steam side than on the liquid side. Except for irregularities in permeability, steam fingers have little tendency to permeability, steam fingers have little tendency to form. The second stabilizing effect, thermal conduction, tends to collapse irregularities at the front of the steam zone because of heat losses normal to the direction of fluid flow.

Laboratory Experiments

The mechanisms involved in the steam distillation process were studied in unconsolidated tubular process were studied in unconsolidated tubular sandpacks. The apparatus used in the high-pressure (2,000 psi) experiments is illustrated in Fig. 2.

JPT

P. 899