Page 195 - Petroleum Geology

172

-LUID PRESSURES V
10 20MPa
I-_
_L

Fig. 8-14. When put onto production, the pressures in the well of Fig. 8-13 are reduced
by friction. Oil flows radially in the reservoir to the well.
Fig. 8-15. Diagrammatic map of potentiometric surface near a producing oil well (contours
at interval x above lowest point on surface). Elevation of the potentiometric surface in-
creases as the natural logarithm of the distance from the well.

2nrt, where t is the thickness of the reservoir and r is the radius to the con-
centric surface. In the well, this area is:
A, = 2nrbt (8.14)
where rb is the radius of the borehole. Let qb be the specific discharge, Q/Ab,
into the well, and q the specific discharge across a concentric surface at radius
r, then:
qb X 2nrbt = q X 2nrt

and :
4 = qbrbIr- (8.15)
Thus the specific discharge varies inversely with distance from the well.
From Darcy 's law, assuming a nearly horizontal reservoir: