Page 32 - A Practical Companion to Reservoir Stimulation

ROCK MECHANICS

EXAMPLE B-2
From Eq. 2- 16,
Calculation of the Effective Stress

If a reservoir is 10,000 ft deep and has a 0.70 oil saturation,
calculate the effective vertical stress. Use the variables given
in Table B- 1. Since no information was given on reservoir pressure,
then
Solution (Ref. Section 2-2.4)
p(, H
The absolute vertical stress is equal to the overburden pres- p=-= (50.5) (10,000) = 3507psi, (B-11)
sure, and from Eq. 2-40, , 144 144

pf H (165) (10,000) and from Eq. 2-14,
-
-
CT = PfgH = -
144 144 CT’ = 11,483 - (0.72) (3507) G 896Opsi. (B-12)
= 11,483psi. (B-7)
To calculate Biot’s poroelastic constant, the total and bulk I pf = 2.65 g/cc [165 Ib/ft3]
compressibilities are required.
p, = 50.5 Ib/ft3
C, = sot, + sw,c,,, + Cl’, (B-8) cf = 3x 10Ppsi
and I c, = 10-5psi

cr = (0.7) (lo-’) + 0.3 (3 x + 3 x
= 1.09 x 10-~~~i-’. (B-9) Table B-1-Formation data for Example B-2.

B-3