Page 200 - A Practical Companion to Reservoir Stimulation

PRACTICAL CONSIDERATIONS FOR FRACTURE TREATMENT DESIGN

coefficients are routinely calculated in the laboratory for based on the amount of hydraulic horsepower the pump
various fluids, these values, for a variety of reasons, may not trucks develop. Therefore, higher pumping pressures increase
be effective in an actual treatment. The best method for the cost of a fracture treatment. Hydraulic horsepower can be
quantifying an actual leakoff value is to follow the method- calculated using the following expression:
ology outlined in Chapter 7 of Reservoir Stimulation. Pressure
%P
analysis has proved to be an invaluable tool in designing HHP= -,
treatments. 40.8
where qi = pump rate (BPM) and p = pressure (psi). Price
P-4.2: Determining the Pump Rate schedules generally increase as hydraulic horsepower in-
Pump rates are best determined by balancing the benefits of creases; the price difference between a 20-BPM treatment
increasing rate to improve fluid efficiency and decreasing and a 401BPM treatment can be significant if the treatment
rate resulting from high friction. One of the best ways to must be pumped down 2%-in. tubing. Using the values for
improve the overall efficiency of a fracturing fluid is to friction pressure drop on Fig. P-29, a standard nondelayed
simply pump faster as demonstrated in Fig. P-48. This figure borate fluid will exhibit 3 10 psi of friction drop per 1000 ft at
clearly points out that considerable volumes of fracturing 20 BPM and 800 psi of friction pressure drop at 40 BPM. The
fluid can be conserved if a treatment can be pumped at a same fluid pumped down 5%-in. casing will exhibit only 38
higher rate. Fluid loss is proportional to the square root of and 55 psi of friction, respectively. Therefore, rate will only
time; so, the benefits of increasing rate are greater for long impact the economics through hydraulic horsepower for
fracture lengths or where initial designed rates are small. The certain tubular and fluid combinations. For cases where the
main key is to minimize the time exposure of the fracturing friction of the fluid is not a major consideration, the increased
fluid to leakoff. rate will benefit the economics through improved fluid effi-
However, higher rates result in higher wellhead treating ciency.
pressures caused by the frictional pressure drop in the treat- It becomes obvious that anticipated surface pressures must
ing tubulars. Charges for pumping equipment are usually be calculated during the process of optimizing the pumping

150,000

100,000
h
m
0
v
a,
5
-
3
0
3
G
50,000

0 500 1000 1500
Fracture Length (ft)

Figure P-48-Effect of pump rate on the fluid volume required to generate a given fracture length.

P-4 1