Caustic Steam Flooding
Authors: Tiab Djebbar , Okoye Christian U. , Osman Mahmoud M. 
Published: December 2007

A laboratory study was undertaken to investigate the potential of improving tertiary oil recovery of intermediate to heavy oils by use of caustic soda as a chemical additive in waterflooding and steam flooding. Seven aspects of this study were examined. In all cases, the process was started with a fresh and similarly water-and oil-saturated sand pack. The sand pack was obtained each time by packing sieved glass beads in the range of 35 to 48 mesh size.

The cases include:weak caustic soda flooding (0.001 g/cm3) of previously waterflooded sand pack followed by steam flood,caustic steam flooding immediately after waterflooding the saturated sand pack,a process similar to Case 2 followed by a second cycle flooding with a higher concentration (0.0015 g/cm3) of caustic steam,waterflooding a saturated sand pack followed by conventional steam flood,caustic flooding of water-saturated sand pack followed by caustic steam flood.cyclic steam/caustic flooding of water-saturated sand pack, anddetermination of the optimal temperature for caustic flood.

The results of these experiments showed that as a chemical additive for tertiary waterflooding and steam flooding, caustic soda substantially improved oil recovery of mildly acidic 18 deg. API gravity oil over conventional waterflood and steam flood. The performance of cool caustic flood as a tertiary recovery mechanism was good at high residual oil saturation and poor at low residual oil saturation. Caustic hot water and caustic steam flooding recovered 14.5% more original oil in place (OOIP) than conventional hot water and steam flooding recovery under similar reservoir conditions.

Introduction

Steam Flooding has been demonstrated to have considerable potential for improving oil recovery from fields containing high viscosity oils. A troublesome aspect of steam flooding, however, is the tendency of steam to override the bottom half of the formation, which becomes essentially flooded by hot to warm water (condensate). It has been observed in most steam floods that the top half of the formation swept by steam has its residual oil reduced almost to near zero, while substantial residual oil saturation is observed in the water-swept portion of the reservoir. Some investigators have suggested that oil/steam ratio could be reduced significantly if suitable additives were found that would reduce oil saturation in the lower portion of the formation overridden by steam and mostly swept by hot to warm condensate.

The wettability of petroleum reservoir rocks and its effect on the displacement of oil by water are still controversial subjects of a large body of literature. Craig gave an excellent review of developments in this field. Many recent investigators generally agree that preferred wettability may not be a discrete value function, oil-wet or water-wet, but may span a continuum between these extremes. Recently it has been noted that a large number of reservoirs are more oil-wet than water-wet and that causing a reservoir to become more water-wet by chemical means during the course of waterflood results in an increase of oil recovery compared with an altered displacement by water alone. Leach et at. demonstrated this using a refined oil containing an amine to stimulate an oil-wet system, and an aqueous acid solution to reverse wettability. Mungan, to using NaOH solution, was able to alter the wettability of each crude-oil/brine/sand system. Under certain circumstances, therefore, caustic waterflooding has been found to increase oil production byflow interfacial tension (IFT) displacement,rigid film breaking, andfavorable wettability alteration.

As early as 1920, Flyeman patented a process using sodium carbonate for separating bitumen from sands.

JPT

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