Computerized monitoring of hydraulic fracturing treatments has been an accepted practice for several years. Not only can a continuous record of the treatment parameters be made, but the real-time bottomhole treating pressure can be determined without the use of a reference string or bottomhole pressure tool. However, to calculate the bottomhole treating pressure, the friction pressure of the fluid or slurry must be determined. For conventional, incompressible oil and water-based fluids friction pressure is a straightforward calculation since rate and proppant concentration are the main considerations. The friction pressure for foam fracturing fluids requires a more complex solution.

A computer van was used to monitor carbon dioxide and nitrogen foam treatments incorporating a reference string or bottomhole pressure tool. The following parameters involved in the calculation of bottomhole treating pressure were examined in this study: injection rate, addition of proppant, effect of proppant on slurry friction pressure and foam hydrostatic head pressure. This paper presents a technique which allows the bottomhole treating pressure to be calculated without the use of a reference string or bottomhole pressure tool. The calculation of bottomhole treating pressure for a foam treatment incorporates a technique to correct the hydrostatic head pressure of carbon dioxide and nitrogen foams. In addition, the different effects of proppant addition on friction pressure between nitrogen and carbon dioxide generated foams are discussed.

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