Page 582 - Petrophysics

PROBLEMS 549

8. Differentiate between fault, joint, and fracture. How do they affect
the fluid flow in petroleum reservoirs?
9. A 5-inch long, 2-inch thick rock sample has only one fracture. The
fracture width was measured as 0.03 cm and it fully penetrates the
rock sample over its entire thickness.

(a) Calculate the surface area of the space created by the fracture
assuming rectangular and elliptical fracture shapes.
(b) Calculate the hydraulic radius of the fracture.

10. A resistivity survey in a well showed a wellbore-corrected mud
filtrate resistivity of 0.1 ohm-m, water resistivity 0.19 ohm-m,
invaded zone resistivity 2 ohm-m, and deep formation resistivity
115 ohm-m. The average porosity of 22%, estimated from log
data, well matches the porosity estimated from cores. Pressure
test analysis as well as cores indicated the presence of natural
fractures in the well. Substantial mud loss was also observed during
drilling of this well, and in neighboring wells. Several outcrops also
indicate the presence of natural fractures in the area. Using log data,
estimate the fracture intensity index and the porosity-partitioning
coefficient.
1 1. A newly drilled well in an oil reservoir was logged. Seismic surveys
and geological studies indicated that the well is located in a faulted
naturally fractured zone, which is a downthrown layer. The average
total porosity (15%) of the system was estimated from cores. Other
known characteristics are:

A = 4,500 acres h=70ft

S, = 0.25 Bo = 1.1 bbl/STB

R, = 0.11 Ohm-m Rt = 80 Ohm-m
Rw = 0.15 Ohm-m m = 1.30

(1) Estimate the porosity partitioning coefficient
(2) Estimate the matrix porosity and fracture porosity
(3) Calculate the total oil in place, STB
(4) Calculate the FII and
(5) Estimate the distance to the nearest fault, if the resistivity of the
invaded zone is 6.5 ohm-m.
(6) Does the presence of a nearby fault change the estimate of total
oil in place?