Category: Production From Natural Gas Reservoirs

Gas flow in a reservoir under transient conditions can be approximated by the combination of Darcy’s law (rate equation) and the continuity equation. In general, which in radial coordinates reduces to From the real gas law, and therefore If the permeability k is considered constant, then Equation (4-64) can be approximated further: Performing the differentiation on the…

A more “exact” deliverability relationship for stabilized gas flow was developed by Aronofsky and Jenkins (1954) from the solution of the differential equation for gas flow through porous media using the Forchheimer (rather than the Darcy) equation for flow. This solution is where D is the non-Darcy coefficient and rd is the Aronofsky and Jenkins “effective” drainage radius, and…

The steady-state relationship developed from Darcy’s law for an incompressible fluid (oil) was presented as Equation. A similar relationship can be derived for a natural gas well by converting the flow rate from STB/d to MSCF/d and using the real gas law to describe the PVT behavior of the gas. Beginning with the differential form…

The formation volume factor relates the reservoir volume to the volume at standard conditions of any hydrocarbon mixture. In the case of a natural gas, the formation volume factor, Bg, can be related with the application of the real gas law for reservoir conditions and for standard conditions. Thus, For the same mass, nR can be cancelled out…

Wichert and Aziz (1972) have presented a correlation that allows the use of the Standing-Katz graph (Figure 4-1) in the presence of nonhydrocarbon gases. In this case corrected pseudocritical values are and where the term ε3 is a function of the H2S and CO2 concentrations given by that can also be obtained graphically from Figure 4-3. Figure 4-3. Pseudocritical…

In the absence of detailed composition of a natural gas, Figure 4-2 can be used to relate the gas gravity (to air) with the pseudocritical properties of gas mixtures. Using the results of Example 4-2, the calculated molecular weight is 18.92, leading to γg = 18.92/28.97 = 0.65. From Figure 4-2, ppc = 670 psi and Tpc = 375°R, which compare with 671 psi and…

Several important works have presented correlations for natural gas properties. Following is a summary of these, with brief descriptions of the use of these correlations.

The behavior of natural gas mixtures can be approximated by the real gas law where Z is the compressibility factor, also called the gas deviation factor in the petroleum engineering literature. The universal gas constant, R, is equal to 10.73 psi ft3/lb-mol-°R. Equation (4-2) is a general equation of state for gases. The gas compressibility factor for mixtures of…

Gas gravity, as used in natural gas production and reservoir engineering, is the ratio of the molecular weight of a natural gas mixture to that of air, itself a mixture of gases. Gas gravity is perhaps the most important defining property of a natural gas because almost all properties and, in fact, the actual description…

Natural gas reservoirs produce hydrocarbons that exist primarily in the gaseous phase at reservoir conditions. To predict the gas production rate from these reservoirs, there is a need to review some of the fundamental properties of hydrocarbon gases. This is particularly important (more so than in the case of oil reservoirs) because certain physical properties…