An Evaluation of Field Projects of Steam With Additives (includes associated papers 23547 and 23587 )

Author:

Castanier L.M.1,Brigham W.E.1

Affiliation:

1. Stanford U.

Abstract

Summary. The use of additives to improve both steamdrive and cyclic steaminjection in field projects has been tested under a variety of conditions. This technique attempts to reduce gravity override and channeling of thesteam by foam generation. Another mechanism appears to be "detergent" cleaning near wellbores by surface-active agents. When successful, this technology seems to be economic even at a low oil price. The results, however, have ranged from excellent to negative. In this paper, we attempt to evaluate the field projects published to date. The results of this study show that the use of additives with steam can provide significant benefits over the use of steam alone. Indeed, addition of surfactant to the steam has proved to be both technically and economically successful when the proper products and procedures were used. Caustics have given mixed results but seem to have been effective in at least one cyclic-steam project. Introduction The late 1970's and the 1980's have seen many attempts to improve steam injection by the use of additives. Although other additiveshave been tried in the field, the most promising technology seemsto be injecting a solution of aqueous surfactant either to increasethe pressure gradient across the region of interest by generation of foam or to use the detergency properties of the surfactant toreduce the oil/water interfacial tension (IFT) and to modify therelative permeability curves. In our opinion, both mechanisms arepresent to some degree in most steam-foam projects. Sixteen field tests of steam with additives have been reviewed. They cover a broad spectrum of reservoirs, oils, depths, andpressures. The type of additive used, the surfactant concentration, thepresence or absence of noncondensable gases and their nature, andthe additive injection mode also varied widely. The effect of thesefactors on the efficiency of the projects is discussed. Some of thefield tests have been performed after extensive laboratory work. The data published on laboratory screening of additives andsupporting field data are used to explain some of the results observedin field testing. This paper obviously does not cover all the field projects on steamwith additives. Some companies choose not to publish their results. We know that successful projects were not reported. It is possible, however, that a slight bias in favor of success exists in thepublished literature. In the field, evidence of mobility control has been sought throughpressure measurements, tracer testing, injectivity profiling, logging, temperature monitoring, and observation wells. Production datahave, of course, been analyzed. The monitoring techniques are alsoevaluated. Of special interest is the use of these monitoringtechniques to identify the recovery mechanisms. Laboratory studies aimed at the determination of surfactantthermal stability and the optimization of a steam/surfactant system arenumerous. One of the earliest was probably the study by Gopalakrisnan et al. in which the emphasis was mostly on IFT lowering. This study demonstrated the need to optimize the injectiontechnique to obtain maximum oil recovery in the laboratory. Dilgren et al. tested surfactants at steam-injection conditions andmeasured the mobility reduction caused by the surfactant compared withwater alone. They also emphasized the use of NaCl to improve thefoam and noncondensable gases to help stabilize it. Theimprovement caused by noncondensable gases was demonstrated again by Falls et al. and Janssen-Vanrosmalen et al. Several studies werecompleted at the Stanford U. Petroleum Research Inst. (SUPRI) on foam flow in sandpacks and surfactant stability atsteam-injection conditions. Refs. 8 through 12 also presentinteresting laboratory studies on various aspects of the steam-foamprocess. In addition, several of the field tests that will be describedfollowed extensive laboratory work; the main features of theresults are described in the papers. Several trends can be identified from the laboratory studies at this stage.A large number of commercially available surfactants arethermally stable and can be used in steam injection.When mobility control is desired, injection of anoncondensable gas with the surfactant solution increases the mobilityreduction of the steam.Introduction of air or oxidants can cause rapid degradation of thesurfactant.The addition of brine has a positive effect on some surfactant systems(notably alpha olefin sulfonates), while it has a negative effect onothers.Some surfactants will affect only the gas mobility, while others alsowill modify the interfacial parameters between oil and water and willaffect the oil/water relative permeabilities. This point is discussedin detail by Ziritt. In addition, optimum foaming and optimuminterfacial properties do not occur simultaneously. A complete discussion of the laboratory work on steamsurfactant systems is inappropriate in this paper. It is important, however, to note that most of the successful field projects presented here have benefited from extensive laboratory testing. Shell Kern River Leases (Mecca and Bishop) Dilgren et al. presented some preliminary results of a field test in the Mecca lease of the Kern River field. Table 1 shows some of the reservoir parameters. The problem seems to be the classiccase of gravity override in a relatively thin, shallow, flat reservoir. The test was performed on four 2.5-acre five-spot patterns. Adifferent surfactant was injected in three wells for testing. Three separate surfactants [Siponate DS-10; Siponate A-168, and Bioterge AS-30(1618)] were injected continuously at aconcentration of 0.5 wt% in the liquid. Salt was added at a concentration of 4 wt% and nitrogen was continuously injected at 3.6 scf/min(about 0.005 mole fraction of the gas phase). The field had beenunder steamdrive for 10 years before the steam-foam projectbegan. Injection pressure rose from 20 to 40 psi before surfactantinjection to 110 to 140 psi with Siponate DS-10, to 155 to 170psi with Siponate A-168, and to 190 to 205 psi with Bioterge AS-30. Pressure gradients in the drive showed a four- toseven-fold increase. The production of the pilot exhibits an increase of32,000 bbl over anticipated production by steamdrive alone. It wasdecided to use Bioterge AS-30 for further work. This surfactantwas later replaced by alpha olefin sulfonates. Recently, Patzek and Koinis gave further results of the Mecca lease pilot and added data from the Bishop Fee pilot, also inthe Kern River field. The pilot consisted of four contiguousinverted five-spots covering 12 and 14 acres, respectively. While the Mecca pilot was a mature steamdrive (10 years), the Bishop lease hadbeen under steamdrive for only 1 year. Both projects werewell-instrumented (eight observation wells in each pilot). Continuousinjection of steam, nitrogen, alpha olefin sulfonate, and salt resultedin increased injection pressure. Copyright 1991 Society of Petroleum Engineers SPERE P. 62^

Publisher

Society of Petroleum Engineers (SPE)

Subject

Process Chemistry and Technology

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