In the study of gas reservoirs in the preceding section, it was implicitly assumed that the fluid in the reservoir at all pressures as well as on the surface was in a single (gas) phase. Most gas reservoirs, however, produce some hydrocarbon liquid, commonly called condensate, in the range of a few to a hundred or more… Continue reading The Gas Equivalent of Produced Condensate and Water

In water-drive reservoirs, the relation between Gp and p/z is not linear, as can be seen by an inspection of Eqs. (4.13) and (4.16). Because of the water influx, the pressure drops less rapidly with production than under volumetric control, as shown in the upper curve of Fig. 4.2. Consequently, the extrapolation technique described for volumetric reservoirs is not applicable.… Continue reading Material Balance in Water-Drive Gas Reservoirs

For a volumetric gas reservoir, Eq. (4.13) can be reduced to a simple application of a straight line involving the gas produced, its composition, and the reservoir pressure. This relationship is routinely used by reservoir engineers to predict recoveries from volumetric reservoirs. Since there is neither water encroachment nor water production in this type of… Continue reading Material Balance in Volumetric Gas Reservoirs

In the previous sections, the initial gas in place was calculated on a unit basis of 1 ac-ft of bulk productive rock, given information on the porosity and connate water. To calculate the initial gas in place on any particular portion of a reservoir, it is necessary to know, in addition, the bulk volume of… Continue reading Calculating Gas in Place Using Material Balance

Under initial conditions, one unit (1 ac-ft) of bulk reservoir rock contains Connate water: 43,560 × φ × Swi ft3 Reservoir gas volume: 43,560 × φ × (1 – Swi) ft3 Surface units of gas: 43,560 × φ × (1 – Swi) ÷ Bgi SCF In many reservoirs under water drive, the pressure suffers an initial decline, after which water enters the reservoir at a… Continue reading Calculating Unit Recovery from Gas Reservoirs under Water Drive

In many gas reservoirs, particularly during the development period, the bulk volume is not known. In this case, it is better to place the reservoir calculations on a unit basis, usually 1 ac-ft of bulk reservoir rock. This one unit, or 1 ac-ft, of bulk reservoir rock contains Connate water: 43,560 × φ × Sw ft3 Reservoir gas volume:… Continue reading Calculating Unit Recovery from Volumetric Gas Reservoirs

In order for the reservoir engineer to calculate the amount of hydrocarbon in place from geological information, the reservoir bulk volume must first be calculated. Many methods exist to estimate the reservoir bulk volume but only two will be discussed here. The first method involves the reservoir engineer using well logs, core data, well test… Continue reading Calculating Hydrocarbon in Place Using Geological, Geophysical, and Fluid Property Data

The contains a discussion of single-phase gas reservoirs (refer to Fig. 1.4). In a single-phase gas reservoir, the reservoir fluid, usually called natural gas, remains as nonassociated gas during the entire producing life of the reservoir. This type of reservoir is frequently referred to as a dry gas reservoir because no condensate is formed in the… Continue reading Introduction