Types of reservoir fluid

Reservoir fluids are broadly cafegorised using those properties which are easy to measure in the field, namely oil and gas gravity, and the producing gasioil ratio (GOR) which is the volumetric ratio of the gas produced at standard condition of femperature and pressure (STP) fo fhe oil produced at STP. The commonly used units are shown in the following table. 

Standard conditions of femperature and pressure are commonly defined as 60°F (298K) and one atmosphere (14.7 psia or 101.3 kPa). 

Oil gravity is most commonly expressed in degrees API, a measure defined by the American Petroleum Institute as 

The API gravity of water is 10°. A light crude oil would have an API gravity of 40°, while a heavy crude would have an API gravity of less than 20°. In the field, the API gravity is readily measured using a calibrated hydrometer. 

There are no definitions for categorising reservoir fluids, but the following table indicates typical GOR, API and gas and oil gravities for the five main types. The compositions show that the dry gases contain mostly paraffins, with the fraction of longer chain components increasing as the GOR and API gravity of the fluids decrease. 

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Figure 5.21 helps to explain how the phase diagrams of the main types of reservoir fluid are used to predict fluid behaviour during production and how this influences field development planning. It should be noted that there are no values on the axes, since in fact the scales will vary for each fluid type. Figure 5.21 shows the relative positions of the phase envelopes for each fluid type. 

There are five types of reservoir fluids. These are usually called black oil, volatile oil, retrograde gas, wet gas, and dry gas. The five types of reservoir fluids have been defined because each requires different approaches by reservoir engineers and production engineers. 

The petroleum engineer should determine the type of fluid very early in the life of his reservoir. Fluid type is the deciding factor in many of the decisions which must be made regarding the reservoir. The method of fluid sampling, the types and sizes of surface equipment, the calcula-tional procedures for determining oil and gas in place, the techniques of predicting oil and gas reserves, the plan of depletion, and the selection of enhanced recovery method are all dependent on the type of reservoir fluid. 

The name black oil is a misnomer since the color of this type of oil is not always black. This type of reservoir fluid has also been called low-shrinkage crude oil or ordinary oil,1,2... 

The third type of reservoir fluid we will consider is retrograde gas. Retrograde Gas Phase Diagram... 

The following notices were taken from the Bryan-College Station Eagle, Sunday, September 15, 1985. Make an estimate of the type of reservoir fluid in each reservoir. 

The average gas-oil ratio produced from the Upper Washita-Fredericksburg formation of the Summerland Field is 275 scf/STB. The gravity of the produced oil is 26°API. The color of the stock-tank oil is black. What type of reservoir fluid is in this formation ... 

One of the wells in the Merit Field, completed in December 1967 in the North Rodessa formation, originally produced 54°API stock-tank liquid at a gas-oil ratio of about 23,000 scf/STB. During July 1969, the well produced 1987 STB of 58°API liquid and 78,946 Mscf of gas. In May 1972, the well was producing liquid at a rate of about 30 STB/d of 59°API liquid and gas at about 2000 Mscf/d. What type of reservoir fluid is this well producing ... 

The initial reservoir pressure and temperature in the Lower Tuscaloosa reservoir of the East Fork Field was 5043 psig and 263°F. The bubble-point pressure of the 40°API oil plus 1110 scf/STB of gas produced from this field was measured as 3460 psig at 263°F. What type of reservoir fluid is in this reservoir Is the reservoir oil saturated or undersaturated How do you know ... 

Producing gas-oil ratio remained constant prior to sampling, so you may assume that the reservoir fluid is single phase. Calculate the composition of the reservoir fluid. What type of reservoir fluid is this ... 

Samples of gas and liquid are taken from a first stage separator operating at 500 psia and 75°F. The separator gas-oil ratio is constant at 2347 scf/SP bbl. The compositions of the samples are given in the table below. The density of the separator liquid at separator conditions, calculated with procedures given in Chapter 11, is 47.7 Ib/cu ft. Calculate the composition of the reservoir fluid. What type of reservoir fluid is this ... 

A work reservoir is similarly defined as any body or combination of bodies, used as part of the surroundings, whose only interaction with the system is one that may be described in terms of work. We may have a different type of reservoir for each mode of interaction other than thermal interaction. A work reservoir then is used to perform work across the boundary separating the reservoir and the thermodynamic system and to measure these quantities of work. In the following we are, in order to simplify the discussion, primarily concerned with mechanical work, but this limitation does not alter or limit the basic concepts. A reservoir for mechanical work may be a set of weights and pulleys in a gravitational field, an idealized spring, or a compressible fluid in a piston-and-cylinder arrangement. In any case the reservoir must... 

In the reservoir imder consideration the energy available for expulsion of oil and gas comes entirely from the evolution of solution gas on pressure reduction. Consequently, this type of reservoir is designated as a solution gas drive reservoir to distinguish it from those whose recovery mechanisms involve energy from the expansion of a gas cap (gas expansion reservoirs) or from the encroachment of water (water drive reservoirs). The behavior of a solution gas drive reservoir may be predicted if the following data are available (1) the original reservoir pressure and temperature (2) values of r, and v as a fimction of pressure (3) values of the reservoir fluid viscosities r as a function of pressure at reservoir temperature (4) the constant water saturation 8w) (5) values of Kg/Ko as a fimction of saturation and (6) the number of barrels of stock tank oil originally in reservoir (iV). The computations are carried out stepwise as shown below. 

Feed to a falling film evaporator is usually introduced under the liquid level maintained at the top of the tubes, so that a reservoir of rather low velocity liquid is available for liquid distribution to the many vertical tubes. In falling film evaporator and re-boiler design, equal fluid distribution among the tubes and film initiation are very important factors. For this reason, a number of sophisticated and very effective hydraulic distributing devices have been developed to handle different types of process fluids.f In order... 

The example of a binary mixture is used to demonstrate the increased complexity of the phase diagram through the introduction of a second component in the system. Typical reservoir fluids contain hundreds of components, which makes the laboratory measurement or mathematical prediction of the phase behaviour more complex still. However, the principles established above will be useful in understanding the differences in phase behaviour for the main types of hydrocarbon identified. 

Another type of experiment involves a fluid filament being drawn upward against gravity from a reservoir of the fluid (101,213,214), a phenomenon often called the tubeless siphon. The maximum height of the siphon is a measure of the spinnabiUty and extensional viscosity of the fluid. Mote quantitative measures of stress, strain, and strain rate can be determined from the pressure difference and filament diameter. A more recent filament stretching device ia which the specimen is held between two disks that move apart allows measurements ia low viscosity Hquids (215). AH of these methods are limited to spinnable fluids under small total strains and strain rates. High strain rates tend to break the column or filament. 

Porous Media Packed beds of granular solids are one type of the general class referred to as porous media, which include geological formations such as petroleum reservoirs and aquifers, manufactured materials such as sintered metals and porous catalysts, burning coal or char particles, and textile fabrics, to name a few. Pressure drop for incompressible flow across a porous medium has the same quahtative behavior as that given by Leva s correlation in the preceding. At low Reynolds numbers, viscous forces dominate and pressure drop is proportional to fluid viscosity and superficial velocity, and at high Reynolds numbers, pressure drop is proportional to fluid density and to the square of superficial velocity. 

A simple manifold is illustrated in Figure 40.41. This manifold contains one pressure inlet port and several pressure outlet ports that can be blocked off with threaded plugs. This type of manifold can be adapted to systems containing various numbers of subsystems. A thermal relief valve may be incorporated in this manifold. In this case, the port labeled T is connected to the return line to provide a passage for the relieved fluid to flow to the reservoir. 

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