Oil and Gas Reservoirs

C02 sequestration [14] in geologic formations includes oil and gas reservoirs, unmineable coal seams, and deep saline reservoirs. These are structures that have stored crude oil, natural gas, brine, and C02 over millions of years. Many power plants and other large emitters of C02 are located near geologic formations that are amenable to C02 storage. Further, in many cases, the injection of C02 into a geologic formation can enhance the recovery of hydrocarbons, providing value-added by-products that can offset the cost of C02 capture and sequestration. 

In some cases, production from an oil or natural gas reservoir can be enhanced by pumping C02 gas into the reservoir to push out the product, which is called Enhanced Oil Recovery (EOR). The United States is the world leader in EOR technology, using about 32 million ton of C02 per year for this purpose. From the perspective of the sequestration program, EOR represents an opportunity to sequester carbon at low net cost, due to the revenues from recovered oil/gas. 

In an EOR application, the integrity of the C02 that remains in the reservoir is well understood and very high, as long as the original pressure of the reservoir is not exceeded. The scope of this EOR application is currently economically limited to point sources of C02 emissions that are near an oil or natural gas reservoir. 

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Nitrogen is used for pressure maintenance in oil and gas reservoirs for enhanced recovery. It is sometimes used as a miscible agent to reduce oil viscosity and increase recovery in deep reservoirs. Other appHcations include recovery of oil in attic formations, gas cap displacement, and a sweep gas for miscible CO2 slugs. Nitrogen competes with CO2, a more miscible gas with hydrocarbons (qv), in most of these appHcations. The production mode is typically by on-site cryogenic separation plants. In 1990, nitrogen production in enhanced recovery operations was 20 x 10 m /d (750 million SCF/d)... 

Common salt, or sodium chloride, is also present in dissolved form in drilling fluids. Levels up to 3,000 mg/L chloride and sometimes higher are naturally present in freshwater muds as a consequence of the salinity of subterranean brines in drilled formations. Seawater is the natural source of water for offshore drilling muds. Saturated brine drilling fluids become a necessity when drilling with water-based muds through salt zones to get to oil and gas reservoirs below the salt. 

Formation water occurs naturally with virtually all oil and gas reservoirs, and is constitutionally similar to seawater in many respects. From a corrosion point of view, however, it differs notably in the following respects ... 

In addition to hydraulic fracturing, there are other stimulation techniques such as acid fracturing or matrix stimulation. Hydraulic fracturing finds use not only in the stimulation of oil and gas reservoirs, but also in coal seams to stimulate the flow of methane from there. 

Bachu S. and Shaw J.C. C02 storage in oil and gas reservoirs in western Canada effect of aquifers, potential for C02-flood enhanced oil recovery and practical capacity. 

The main conclusion of this study is that hydrocarbon-based surface geochemical methods can discriminate between productive and non-productive oil and gas reservoir areas. Variables in surface soils that best distinguish productive and non-productive areas are ethane and n-butane and heavy (C24+) aromatic hydrocarbons. Heavy metals (U, Mo, Cd, Hg, Pb) are possibly indirect indicators of hydrocarbon microseepage, but they are more difficult to link with the reservoirs. 

Some oil and gas reservoirs contain large volumes of produced natural gas or carbon dioxide (CO2). This gas is produced simultaneously with the liquid hydrocarbons. The natural gas or CO2 is recovered, recompressed, and reinjected into the gaseous portion of the reservoir. The reinjected natural gas or CO2 maintains reservoir pressure and helps push additional liquid oil hydrocarbons out of liquid portion of the reservoir. 

Storage capacity assessments of Canadian sedimentary basins, coal seams and oil and gas reservoirs. 

The Rose Run Sandstone is the best characterized of the Cambrian sandstones because it is also an oil and gas reservoir (Fig. 3). It is also the only one of the Cambrian sandstones that is known to retain its sandstone composition in the eastern part of the state rather than passing laterally into carbonate. The Rose Run Sandstone is a sandy layer in the middle of the Knox Dolomite (Fig. 4), which across much of eastern Ohio lies at depths suitable for injection of supercritical C02 (Fig. 3). The Rose Run Sandstone was deposited in a passive margin phase of the Appalachian Basin and consists of interbedded layers of carbonate, primarily dolos-tone, and sandstone (Fig. 5). The sandstone is compositionally mature, consisting largely of quartz. Subordinate reactive minerals are the alkali feldspars and locally abundant glauconite (Fig. 5). Dolomite and quartz are the dominant cements (Janssens 1973 Riley et al. 1993). 

The fundamental phases of petroleum production include (1) the initial exploration required to find heretofore undiscovered oil and gas reservoirs (2) primary and secondary recovery methods, which make use of both naturally occurring (or primary) reservoir energy and the application of secondary energy sources, such as the injection of gas or water and (3) enhanced oil recovery used to increase ultimate oil production beyond that achievable with primary and secondary methods. Enhanced oil recovery (EOR) methods increase the proportion of the reservoir by improving the sweep efficiency, reducing the amount of residual oil in the swept zones (increasing the displacement efficiency), and reducing the viscosity of thick oils. 

The exploration required to identify previously undiscovered oil and gas reservoirs is grossly affected by the economics and politics of the worldwide oil markets (supply and demand). The experience of one year cannot easily be extrapolated to that of subsequent years. 

It is convenient to classify oil and gas reservoirs in terms of the type of natural energy and forces available to produce the oil and gas. At the time... 

Furthermore, Azerbaijan is planning an annual production of up to 24-30 bcm. The potential of already exploited oil and gas reservoirs for associated gas and other gas reservoirs that are under exploration, provides an export potential of approximately 16-20 bcmp.a. in foreseeable future. 

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