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Enhanced Oil Recovery Techniques and Nitrogen Injection Bandar Duraya AI-Anazi King Saud University, Riyadh, Saudi Arabia Introduction The present state of modern industrial development is characterized by the consumption of enormous quantities of petroleum. It is not used simply for the production of various fuels and lubricants; with each passing year more and more petroleu m is u se d for man ufa ct uri ng sy nthe tic ru b be r, synthetic fibers, plastics, drugs, and thousands of other products. While demand for pe rise, petroleum prod lon oriá However, new devel World Oil prices give otherwise neglected uaus to eady decline. d the rise in portions of se new technical developments fall under the broad heading of enhanced Oil recovery COR). Enhanced Oil recovery is a collection of general methods, each with its own unique capability to extract the most Oil from a particular reservoir. Each has been investigated rather thoroughly both from a theoretical and laboratory perspective, as well as in the field Over the years, interest in enhanced Oil recovery (EOR) has been tempered by the increase in Oil reserves and production. Many techniques have been investigated in the laboratory and the field for improving Oil recovery.

Historically the iscovery of major Oil fields in the world added large volu Swlpe to vlew next page volumes of Oil to the worldwide market. In addition, estima tes o f re se rves fro m res ervoirs in the M id dl e Eas t increased significantly, leading to the expectation that the Oil supply would be plentiful. Although large volumes of Oil remain in mature reservoirs, the Oil Will not be produced in large quantities by EOR processes unless these processes can compete economically with the cost of Oil production from conventional sources.

Thus, as reservoirs age, a dichotomy exists between the desire to preserve producing wells for otential EOR processes and the lack of economic incentive because of the existence of large reserves of Oil in the world. During the life of a well, Oil recovery has three stages or categories which are: 1 -Primary Oil Recovery 2-Secondary Oil Recovery 3-Tertiary Oil Recovery The term enhanced Oil recovery (EOR) basically refers to the recovery of Oil by any method beyond the primary stage of Oil production. It is defined as the production of crude Oil from reservoirs through processes taken to Increase the primary reservoir drive.

These processes may include pressure maintenance, injection of displacing fluids, or other methods uch as th erma I tech ni que s. The re fo re, by defini tion, EOR techniques include all methods that are used to increase cumulative Oil produced (Oil recovery) as much as possible. Enhanced Oil recovery can be divided into two major types of techniques: thermal and non-thermal recovery. Non-Thermal Recovery two major types of Non-thermal recovery techniques can be broken down into the following• Pressure Maintenance.

M ore complete recovery of Oil is ac hie ved by spe cia I techn olog ical methods. A common method employed today is artificial maintenance of formation pressure. This traditional step for increasing Oil recovery nvolves the injection offluid into (or near) an Oil reservoir for the purpose of delaying the pressure decline during Oil production. Pressure maintenance can significantly increase the amount of economically recoverable Oil over that to be expected with no pressure maintenance. Waterflooding.

Production can be increased after a decline in pressure from the water drive or pressure maintenance by a technique called waterflooding, which is the injection of water through injection wells to push crude Oil toward producing wells. Water is pumped into the productive layer at injection pressure through bore holes in a volume equal to or greater than) the volume of Oil extracted. So, the formation energy in the depost is kept at the optimum level. The original lifetime of the well is prolonged, which greatly reduces the amount of drilling operations and consequently reduces the cost of the Oil.

Gas Injection. T here are two major types of gas injection, mis ci bl e gas inj ect ion an d immis cib le g as inje ct ion. In mis ci bl e gas in je ct io n, the ga s is inj ec ted a t or ab ove minimum miscibility pressure (MMP) which ga s in je ct io n, the ga s is inj ec ted a tor ab ove minimum miscibility pressure (MMP) which causes the gas to be miscible in the oil. On the other hand in immiscible gas injection, flooding by the gas is conducted below MMP. ThlS low pressure injection of gas is used to maintain reservoir pressure to prevent production cut-off and thereby increase the rate of production.

Gas injection processes can be broken down into the following techniques: Liquefied Petroleum Gas Miscible Slug. Displacement by miscible slug usually refers to the injection of some liquid solvent that is miscible upon first contact with the resident crude oil. In particular, this process uses a slug of propane or other liquefied petroleum gas (2 to 5% PV [pore volume]) ailed by natural gas, inert gas, and/or water. Thus, the solvent Will bank Oil and water ahead of it and fully displace all contacted Oil. Enriched Gas Miscible Process.

In the enriched gas process, a slug of methane enriched with ethane, propane, or butane Continued on Page 29 28 CSEG RECORDER oct0ber 2007 Article Contd Enhanced Oil Recovery Techniques and Nitrogen Injection Continued from Page 28 (10 to 20% PV) and tailed by lean gas and/or water is injected into the reservoir. When the injected gas contacts virgin reservoir Oil, the enriching components are slaked from the injected gas and absorbed into the oil. High Pressure Lean Gas M . This process involves PAGF This process involves the continuous injection of high pressure methane, ethane, nitrogen, or flue gas into the reservoir.

The lean gas process, similar to enriched gas, involves multiple contacts between reservoir Oil and lean gas before forming a miscible bank. But, there is a difference in the enriched gas process where light components condense out of the injected gas and into the oil, then intermediate hydrocarbon fractions (C2 to C6) are stripped from the Oil into the lean gas phase. Carbon Dioxide Process. Oil displacement may be initiated by a number of mechanisms due to injection of COZ into Oil eservoirs. Carbon dioxide is not usually miscible with reservoir Oil upon initial contact, however it may create a miscible front like the lean gas process.

Sor there are two major types of C02 floods; miscible flood in which the gas is injected at or above the MMP, and immiscible flood in which flooding by the gas is co nd uc ted b elow the Miscibility is initiated by the extraction of la rge am oun ts of h ea vie r hydrocarbons (C5 to C30) by C02. Chemical Processes. Chemical flood is another technique to increase the mobilio,’ of Oil in order to enhance Oil recovery. This technique is based on adding additives or chemicals to the isplacing fluid or to the residual Oil to control viscosity and interfacial tension.

Chemical process flooding. Micellar Polymer Flooding. Micellar solutions are mixtures of surfactants, co su rfa ct a nts, elec tro ly tes, h y drocarbon, and water. Surfactants are substances known as surface active agents, such as soap. Cosurfactants are used for stability such as alcohols. Electrolytes are salts used to control viscosity and interfacial tension such as sodium chloride or ammonium sulphate. Hydrocarbon used is light crude at most. These solutions, which are designed on a field by field basis, are proposed to displace reservoir Oil nd miscible water.

Caustic Flooding. An in situ emulsifica tio n p roce ss is emp loy ed by ca us tic or al ka li ne inje ct ion . Th e a dd ed c he mical sto th e in je ct ion water are caustic soda, sodium silicate, sodium carbonate, or sodium hy d roxide . Th es e ch emic al sare mixed with the residual Oil in the reservoir. The crude Oil must contain natural organic acids; most common are the naphthenic acids. When the alk aline inj ecte d water a nd aci dic crude react, soaps are produced at the Oil water interface. These soaps cause Oil to be movable.

Polymer Flooding. Polymer floods a re impro ved water floods by ncrea si n g th e viscosity of th e Continued on Page 30 october 2007 CSEG RECO efficiency. In addition, increasing the displacing fluid’s viscosity and loweri ng its re lative pe rmea bi li tyth ro ug h pl ug gi ng wil I improve the mobility ratio and this WIII make an improvement in areal and vertical sweep efficiency. Steam Injection. Heat is injected into a reservoir to reduce the Oil viscosity and, consequently, to improve the displacement efficiency.

As a result of improved mobilization efficiency crude is expanded and flows easily through the porous media toward the wellbore. Thermal Recovery. Thermal recovery refers to Oil recovery rocesses in which heat plays the principle role. The most widely used thermal techniques are in situ combustion, continuous injection of hot fluids such as steam, water or gases, and cyclic operations such as steam soaking. The process may involve steam soak that is sometimes called steam stimulation or “huff and puff’. In this process, steam is injected down a producing well at a high injection rate, after which the well is shut in.

The injected steam heats up the area around the well bore and increases recovery of the Oil immediately adjacent to the well. After a short period of injection EOR METHODS Non-Therm al Water flood Chem ical Floo d nductio n Stimul ation Alkaline F loodi ng Combinatio n with Chemicals Emulsion Floodi ng Hot Waterflooding Miscib le (Solv ent) In situ combus tion Combinatio n Forward Combustio n Reverse Mining Figure 1. EOR Methods (After Sarma, 1999. ) Figurel : EOR Methods (After Sarma, 1 gg g ) 30 CSEG RECORDER october 2007 Continued on Page 31 Cont’d technology of handling liquids colder than -187CF is called cryogenics.

All the liquids and the equipment to handle these cold liquids are considered cryogenic As previously discussed one of the enhanced Oil recovery methods is gas injection. In miscible gas injection, the gas is injected at or above the minimum miscibility pressure (MMP) which causes the gas to be miscible in oil. When flooding by the gas is conducted below MMP it is known as immiscible gas injection. Primary conditions affecting miscibility are: composition, fluid characteristics, pressure, and temperature.

One gas employed for these gas Injection techniques is nitrogen Nitrogen has long been successf ully used as the injection fluid for EOR and widely used in Oil field operations for gas cycling, reservoir pressure maintenance, and gas lift. The costs and limitations on the availability of natural gas nd C 02 ha ve mad e n itro ge na n economic alternative for Oil recovery by miscible gas displacement. Nitrogen is usually cheaper than C02 or a hydrocarbon derived gas for displacement in EOR applications and has the added benefit of being non-corrosive.

History of Nitrogen There are few known correlations to determine the MMP of nitrogen since the a vai lab le litera tu re dat a on the MMP of nitrogen with crude Oils and synthetic Oil are scarce. Nitrogen MMP of different Oils is a function of the temperature, reservoir fluid com osition, and pressure on miscibilitv. and pressure on miscibility. Determination of the MMP of nitrogen ith the particular Oil is necessary to ensure the successful operation of the misc ib le flood. The re fo re, re se arch ne ed s to be done to exemplif y the process for determination of the MMP fo r n itrog en.

Here we Will b ri efly discuss the nitrogen injection process a nd the determina tion of ni tro ge n MMP. I t is hop ed in the fut ure to develop a more accurate and reliable co r rela tion for estima tln g ni tro ge n Continued on Page 32 October 2007 CSEG RECORDER 31 Article Cont’d Continued from Page 31 liquids and cryogenic equipment. Special steels and aluminium are the most widely used cryogenic construction materials; owever, copper and bronze alloys are also used for specific applications (Dowell (1982), Barber (2005)). efining, public utility, missile, and food processing industries. Recent developments with liquid nitrogen for food preservation show a strong growth potential for nitrogen use in this industry. Interest in nitrogen for Oil and gas well stimulation work is focused on the compact source of high energy gas available at a reasonable cost- Without expensive compressor equipment, gas 1 5,000 psi pressure is available for well stimulation use through liquid nitrogen and its cm,’ devices (Dowell (1982),