Page 64 - Standard Handbook Petroleum Natural Gas Engineering VOLUME2

52 Reservoir Engineering

a comparison of Newman's data with Hall's correlation for consolidated sand-
stones, friable sandstones, and unconsolidated sandstones. While the general
trend of Newman's data on consolidated sandstones (Figure 5-35b) is in the same
direction as Hall's correlation, the agreement is again poor. Figure 5-35c shows
no correlation for Newman's friable sandstones and Figure 5-35d for uncon-
solidated sandstones shows an opposite trend from the correlation presented by
Hall. From Newman's data, ranges of compressibilities for various types of
reservoir rocks are given in Table 5-11. Clearly, formation compressibility should
be measured with samples from the reservoir of interest.

Table 5-11
Range of Formation Compresslbilities
~~ ~ ~
Formation Pore volume compressibility, psi-'
Consolldated sandstones 1.5 x lo4 to 20 x 10-B
Consolidated limestones 2.0 x 10-g to 35 x lo+
Friable sandstones 2.5 x 10-8 to 45 x 106
Unconsolidated sandstones 5.5 x 10-B to 85 x 106

Properties of Rocks Containlng Multiple Fluids

Total Reservolr Compressibility
The total compressibility of oil- or gas-bearing reservoirs represents the
combined compressibilities of oil, gas, water, and reservoir rock in terms of
volumetric weighting of the phase saturations:

ct = coso + cpw + cgsg + Cf (5-64)
where c, is the total system isothermal compressibility in vol/vol/psi, c,,, c,, c
and ct are the compressibilities in psi-' of oil, water, gas, and rock (pore volumef
respectively, S is fluid saturation, and the subscripts 0, w, and g refer to oil,
water, and gas, respectively.
Based on the treatment by Martin [72], Ramey [26] has expressed volumes
in terms of formation volume factors with consideration for gas solubility effects:
c, = so[ ?( %) - &(%)I + s, [ $( %) - (31

(5-65)

where p is pressure in psi, Rs is the solubility of gas in oil in scf/STB oil, R,
is the solubility of gas in water in scf/STB water, and Bg, Bo, and B, are the
formation volume factors of gas, oil, and water, respectively.
Fluid and rock compressibilities have been discussed in prior sections of this
chapter. Table 5-12 provides a summary of these data.