Interpretation - Cased-Hole Log Analysis and Reservoir Performance Monitoring - page 132

Note that the cross-sectional area referred to is the net area available for flow in
the casing/tool annulus. Thus, both the ID of the casing and the OD of the tool must
be known in order to solve the flow equation accurately. This net area may be cal-
culated from:

é

2 2

ù

æ
ç

Casing ID ö

÷

- æ

Tool OD ö

÷

A = p

ê
ê

ú
ú

ç

2 2

This type of calculation may be performed either using a calculator or, graphically,
using a chart of the type shown in Fig. 10.2 . On the graph, the Y -axis plots the
heavy-phase flow rate and the X -axis the light-phase flow rate. In Fig. 10.2 , there
are two series lines. One set (running diagonally from NW to SE) corresponds to
constant total flow rate. Another set (running diagonally from NE to SW) corre-
sponds to constant values of heavy-phase holdup, y h . To solve for the light and
heavy-phase flow rates the analyst should enter the chart and locate the intersection
of the total flow rate ( Q t ) and the heavy-phase holdup ( y h ). From that point the cor-
responding flow rates can be read by moving leftward, parallel to the x -axis for the
heavy-phase flow rate and down the page, parallel to the y -axis to obtain the light-
phase flow rate.

ë û

Question #10.2
Oil and water flow in 5-in. 15.5-lb casing which has an ID of 4.95 in. The slip
velocity, V s , is 20 ft/min. The water holdup has been found from a gradiomanometer
survey to be 0.7. Assume that a one 11/16-in. OD tool was used to make the mea-
surements, and that the total flow rate is 1,000 B/D.

(a) What is the water flow rate?
(b) What is the oil flow rate?

Note also that the chart shown in Fig. 10.2 is specifically built for a given set of
values for casing size and weight (and therefore casing ID), tool OD, and slip veloc-
ity, V s . If the analyst chooses to use the graphical method, an appropriate chart
should be obtained from the relevant service-company publication to suit the par-
ticular circumstances.

Flowmeter and Gradiomanometer Combinations

As an example of the practical method to be employed, the log shown in Fig. 10.3
will be considered. This well produces oil and water from two perforated intervals.
Total flow rate is 850 B/D (at down-hole conditions) with 485 BOPD and 365
BWPD. Down-hole fluid densities are 1.05 g/ cc for the water and 0.8 g/cc for the
oil. The objective of the analysis is to deduce the oil and water flow rates at each
station where a total flow rate has been determined and thereby to determine the oil
and water production rates from each perforated interval.