Everything up to this point applies to a perfect or ideal gas. Actually there are no perfect gases; however, many gases near atmospheric temperature and pressure approach ideal behavior. All molecules of real gases have two tendencies: (1) to fly apart from each other because of their constant kinetic motion and (2) to come together… Continue reading Real Gas Law
Specific Gravity
Because the density of a substance is defined as mass per unit volume, the density of gas, ρg, at a given temperature and pressure can be derived as follows: where Mw = molecular weight Because it is more convenient to measure the specific gravity of gases than the gas density, specific gravity is more commonly used. Specific gravity is defined as… Continue reading Specific Gravity
Review of Gas Properties
Ideal Gas Law Relationships that describe the pressure-volume-temperature (PVT) behavior of gases are called equations of state. The simplest equation of state is called the ideal gas law and is given by where p = absolute pressure V = total volume that the gas occupies n = moles of gas T = absolute temperature R′ = gas constant When R′ = 10.73, p must be… Continue reading Review of Gas Properties
Fluid Saturations
The ratio of the volume that a fluid occupies to the pore volume is called the saturation of that fluid. The symbol for oil saturation is So, where S refers to saturation and the subscript o refers to oil. Saturation is expressed as either a fraction or a percentage, but it is used as a fraction in equations. The saturations of all… Continue reading Fluid Saturations
Isothermal Compressibility
The isothermal compressibility for a substance is given by the following equation: where c = isothermal compressibility V = volume p = pressure The equation describes the change in volume that a substance undergoes during a change in pressure while the temperature is held constant. The units are in reciprocal pressure units. When the internal fluid pressure within… Continue reading Isothermal Compressibility
Porosity
The porosity of a porous medium is given the symbol of φ and is defined as the ratio of void space, or pore volume, to the total bulk volume of the rock. This ratio is expressed as either a fraction or a percentage. When using a value of porosity in an equation, it is nearly always expressed… Continue reading Porosity
Review of Rock Properties
Properties discussed in this section include porosity, isothermal compressibility, and fluid saturation. Although permeability is a property of a rock matrix, because of its importance in fluid flow calculations, a discussion of permeability is postponed until in which single-phase fluid flow is considered.
Introduction
As fluid from a reservoir is produced and brought to the surface, the fluid remaining in the reservoir experiences changes in the reservoir conditions. The produced fluid also experiences changes as it is brought to the surface. The reservoir fluid typically sees only a decrease in pressure, while the produced fluid will experience decreases in… Continue reading Introduction
Peak Oil
Since oil is a finite resource in any given reservoir, it would make sense that, as soon as oil production from the first well begins in a particular reservoir, the resource of that reservoir is declining. As a reservoir is developed (i.e., more and more wells are brought into production), the total production from the reservoir… Continue reading Peak Oil
Production from Petroleum Reservoirs
Production from petroleum reservoirs is a replacement process. This means that when hydrocarbon is produced from a reservoir, the space that it occupied must be replaced with something. That something could be the swelling of the remaining hydrocarbon due to a drop in reservoir pressure, the encroachment of water from a neighboring aquifer, or the… Continue reading Production from Petroleum Reservoirs