This paper vies pfepared for preeentatiin at the SPE/lME NmIh Sympoaum on lmProvwJ OilReUIVWY held in Tul~, oklah~a, U.S.A., 17-~A@ 1T his peper was eekcted for Pmsentetion by en SPE Program committee following review of information contained in an abstract submitted by the euthorts). Contents of the paper, ee presented, have not been reviewed by tfw Socii of Petroleum Engineere end are subject to correction by the author(s). The materiel, as preeented, does nOt n eceswiiy reflect anY P@tin of the society of Petroleum Engitwers, M offkwe, of member% Papem prmemfed et SPE meetlnge em subject to publication review by Edltofiel Commhtees of the Scciety of Petmfeum EngineW8. Permission 10copy is restrictedto en abstract of not mcfe than 300 words, IllustretiormITMYnc4be copkd. The atmtmcl shoutdcontain ccmspkucus acknowledgment of wfmre end by whom the paper is presented. Write Lbr.srian, SF'E. P.O. Box -, Rich-d-m~7~1 U.S.A., Telex 16SS4S SPEUT.

Tlua paper wu prepared for~semauon aI tic I Y% SPE Europmn PeLIokumCunf.mence kld in Milm, IIIIY. 22-24 I!'w4w 1996. This paper was selecld lor presentatco by tfw SPE Program Ccmmitle.s fdwq _ C4rnfcmmaticm ccmtamed in an abslracl sumnmed by tfw author(s). Ombmts ot Iheã s presentd. fwa not km rwiewed W the SIXiaty of Petroleum Engiwws ard am Wbfectto KJlrq,h~lfw Wllhor(s) Th e material, as presented, dces nol -b rdlect any psttm o It!+ %xiety of Petroleum EIWJimeIS o, its members. Papers Fesenled al SPE meetmgs are su to puhkaticm review by Edttonal Committee al tie Scci* of Petro!e.Im~eers %Lsti to copf IS r.astccted m an abstract of rot more !han X0 wcrds. Ilustratlcos may not by coped. TM abstract sfwukl amtarn R%H'%15%%%!?&Rkhmc15cm, TX7508S+Y3S6 "s.faxol.,,'+w?-,.ts, mt d nbem ar!d by Acw the FE$B! was presented WMe Abstract This paper givesa critical overview of field experience with the use of foam for improved sweep efficiency and control of produced gas in the Former Soviet Union, i n the North Sea and in North America. The field practice demonstrates a wide specter of foam application and reservoir problems which the foam processes-can mitigate.Foam applications are classified as injector and producer treatments for gas and water shut-off. Foam was applied in combination with different recovery strategies such as gas and WAG injection, steam injection, in-situ combustion and waterflooding. The choice of foamer and foam placement strategy are important and depend on the reservoir and type of the problem to address. Many technical failures are explainable by erroneous problem definition.The novelty of the present overview is that it gives a comparison of foam applications in three different geographical areas with different field histories, constraints and requirements on production handling facilities. The review of foam applications in the Former Soviet Union covers field applications of foam in Russia, Azerbaijan and Kazakhstan. The paper also discusses interesting field examples, previously unpublished with application of new foam processes including polymer enhanced foam and foam treatment for water diversion and shut-off.

Water alternate gas (WAG) injection technology is a method which may improve oil recovery efficiency by combining effects from two traditional technologies -water and gas flooding. Both microscopic oil displacement and sweep efficiency can be improved by WAG implementation. This paper describes a method of designing an effective waterlgas flooding in stratified reservoirs.The analytical approach taking into account effects of three phase flow, gravity and viscous forces in anisotropic media, allows the determination of optimum parameters of waterlgas injection. A three-phase extended black oil simulator with relative permeability and capillary pressure hysteresis, was used to validate the optimum WAG injection parameters obtained by the analytical method. In this work, the efficiency of different injection schemes was compared. Simulation results which demonstrate the influence of WAG injection parameters, as water-gas ratio, injection rates and cycle periods, on the recovery process, are discussed.

Cyclic injection is a process that improves waterflooding efficiency in heterogeneous reservoirs. The concept of cyclic injection is based on (1) pulsed injection and (2) alternating waterflood patterns. Cyclic injection has been successfully applied in a number of sandstone and carbonate oil fields in Russia. In the rest of the world, pulsed injection has had limited application, and only in naturally fractured reservoirs. Although changing the waterflood patterns is a common approach to deal with increasing water cuts, a more systematic approach with both pulsed injection and alternating flow directions is not.Cyclic injection has the greatest potential for improved recovery in heterogeneous, high-permeability-contrast sandstones and in naturally fractured carbonates and dolomites. The efficiency of the process is high in preferentially water-wet rocks saturated with compressible fluids. Capillary pressures and relative permeability effects are responsible for the improved cyclic oil displacement at the micro level. Improved sweep of the less permeable layers in communication with more permeable thief zones, better horizontal sweep achieved by changing waterflood patterns, and alternating the dominance between gravity and viscous forces are the key effects of cyclic injection on the macro level.The potential of cyclic injection at the Lower Tilje/Åre formations of the Heidrun Field in the Norwegian Sea has been evaluated. Some of the reservoir levels are highly heterogeneous, with large permeability contrasts vertically and horizontally. The current drainage strategy for these formations is water injection, with gas lift in producers when needed. Cyclic injection will improve waterflooding efficiency at virtually zero additional cost. Improved sweep, accelerated oil production, and reduced water cut are the main positive effects expected from cyclic waterflooding. The reserves are predicted to increase by 5 to 6% from the targeted reservoirs at Heidrun after 10 years of cyclic waterflooding.

The cyclic injection process to improve water flooding in carbonate reservoir was evaluated in laboratory experiments, as well as analytical and numerical simulations. Laboratory cyclic injection experiments were performed on a carbonate rock sample with an artificial horizontal fissure. Live oil was established by in-situ recombination of dead oil with hydrocarbon gas at reservoir temperature and bubble point pressure. The experiments were designed by numerical simulation of the cyclic process. Analytical modelling was done to evaluate cyclic injection sensitivity to critical reservoir and process parameters. The cyclic water injection experiments above oil bubble point pressure increased oil recovery by additional 2.9% of Oil Originally In Place (OOIP) above ordinary water flood. This effect can be attributed to the hasten imbibition of water into the matrix during pressurisation half-cycles and capillary retained water in the fine pores in the matrix resulting in oil counter current flow from matrix to the fracture during de-pressurisation half-cycles. Cyclic injection below bubble point pressure, designed to ensure gas saturation not exceeding the critical level, yielded additional recovery of 5.9% of OOIP. This effect may be credited to the energy of released gas, expelling the matrix oil into the fracture. The experimental results indicate significant potential of cyclic injection to improve micro level displacement efficiency of waterflood in carbonate reservoirs. If cyclic water injection is applied at field scale, sweep efficiency improvement from flow pattern redistribution could make an additional contribution. This has been reported by several field cases in the US, China and Former Soviet Union (FSU). Introduction The concept of cyclic injection is based on (1) pulsed injection and (2) alternating waterflood patterns [1–4]. Cyclic injection appears to have the greatest potential in heterogeneous, permeability-contrast reservoirs, with light, high compressibility fluids. Cyclic or pressure pulsing injection has been successfully applied in a number of sandstone and fractured carbonate oil fields in Russia, USA and China [1, 5–8]. Reduction of water production and acceleration of oil extraction rates were observed at several field applications. In the cyclic process, water injection rates are changed between high and low values, in a periodic fashion. The cycle periods at field scale are typically in the range of days to months, much different from the known pulsed pressure technique, where several pressure pulses are applied in time intervals of minutes. Laboratory and field applications of cyclic water injection indicate that additional oil recoveries in the range of 2–15% can be achieved with significant reduction in water cut levels, making the process very attractive and profitable [13,14,15].