Oil-recovery Techniques

Microbid-enhanced oil recovery (MEOR) was first proposed in 1926 by A. Beckman [1780], Between 1943 and 1953, C. E. Zobell [1903,1904] laid the foundations of MEOR techniques. The results were largely dismissed in the United States because there was little interest in finding methods to enhance the recovery of oil at this time. However, in some European countries, the interest for MEOR increased and several field trials were conducted. The first MEOR water flood field project in the United States was initiated in 1986. The site selected was in the Mink Unit of Delaware-Childers Field in Nowata County, Oklahoma [268]. 

Microbiologists laid the foundations of MEOR. After the petroleum crisis in 1973, the interest in MEOR generally increased [1074]. Monographs about the underlying ideas and the practice of MEOR are available [1236,1884]. 

The very methods, ranging from a single well treatment to fieldwide treatments, can be subsumed as MEOR techniques. The injection of microbes into the formation is a common practice in all of these techniques. This should stimulate the in situ microflora, resulting in the production of certain compounds that increase the oil recovery of exhausted reservoirs. The following basic effects can be achieved by microbes [1780]  

It is often stressed that the technology is environmentally friendly. The stimulation of oil production by in situ bacterial fermentation is thought to be initialized by one or a combination of the following mechanisms  

Improvement of the relative mobility of oil to water by biosurfactants and biopolymers 

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Domestic petroleum, natural gas, and natural gas Hquids production has declined at a rate commensurate with the decrease in reserves (see Table 2). Consequently, the reserves/production ratio, expressed in years, remained relatively constant from about 1970 through 1992, at 9—11 years (16). Much of the production in the early 1990s is the result of enhanced oil recovery techniques water flooding, steam flooding, CO2 injection, and natural gas reinjection. 

In principle, the nonmining recovery of bitumen from tar sand deposits is an enhanced oil recovery technique and requires the injection of a fluid into the formation through an injection weU. This leads to the in situ displacement of the bitumen from the reservoir and bitumen production at the surface through an egress (production) weU. There are, however, several serious constraints that are particularly important and relate to the bulk properties of the tar sand and the bitumen. In fact, both recovery by fluid injection and the serious constraints on it must be considered in toto in the context of bitumen recovery by nonmining techniques (see PETROLEUM, ENHANCED OIL RECOVERY). 

A clear solution of aluminum citrate neutralized to pH 7 is used for in situ gelling of polymers in polymer flooding and well stimulation in enhanced oil recovery techniques (128—132). The citrate chelate maintains aluminum ion solubiUty and controls the rate of release of the aluminum cross-linker. 

A. H. Al-Khafaji. Implementations of enhanced oil recovery techniques in the Arab world are questioned. In Proceedings Volume,... 

Kg. 24. Enhanced oil recovery techniques employ heat, gases, chemicals, and water—singly or in combinations—to reduce the factors that inhibit oil recovery and to augment reservoir energy. (Exxon Corp)... 

Air injection an oil recovery technique using air to force oil from the reservoir into the wellbore. 

Crude oil becomes trapped in porous media as a result of capillary forces. The reduction of these forces is required for the recovery of residual oil, and this is the basis of enhanced oil recovery. In practice capillary forces are reduced primarily by lowering interfacial tension between oil and water phases, although increasing the viscosity of the water is also important. Lowering interfacial tension leads to the formation of emulsions and microemulsions, which are of great importance in enhanced oil recovery techniques. 

Vapor and liquid phases coexist in virtually all areas of petroleum production operations, including reservoirs, wellbores, surface-production units, and gas-processing plants. Knowledge of fluid properties and phase behavior is required to calculate the fluid in place, fluid recovery by primary depletion, and fluid recovery by enhanced oil recovery techniques such as gas cycling, hydrocarbon solvent injection, and C02 displacement. Because of the complex nature of petroleum reservoir fluids and the often complicated phase behavior observed at elevated temperature and pressure conditions, the fluid properties and phase behavior historically have been measured experimentally. The complex nature of the fluids arises because of the supercritical components which are dissolved in the mixture of paraffinic, naphthenic, and... 

Commercial production from the shallow parts of the reservoirs with low temperatures and high viscosity oil will require use of thermal and miscible enhanced oil recovery techniques. 

The adsorption of surfactant molecules at oil-water interfaces has attracted much interest, in relation to the oil recovery techniques (1). The systems containing oil, water and emulsifier molecules form generally two phases an aqueous phase containing sometimes solubilized oil in the form of small droplets surrounded by emulsifier molecules and an oil phase which also can contain solubilized water. When the amount of emulsifier is large enough, the system can form only one phase, i.e. all the water (or oil) can be solubilized in the oil (or water). The system is again a dispersion of very small droplets of water (or oil), surrounded by emulsifier molecules, in a continuous medium containing the oil (or water). Such dispersions are currently called microemulsions. The droplet size is usually of the order of lOOA (2). 

PCBs less dense than water, such as PCB-contaminated oils, will float on the water surface and require usual oil-recovery techniques while those that are heavier will sink rapidly in water and will require dredging of sediments. 

The viability of the enhanced oil recovery technique is therefore dependent on the amount of miCTO ulsion injected and the salt content in the medium. It is... 

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