Combination Foam/Fluid Fracturing

Abstract This paper describes the newly developed combination foam/fluid fracturing technique, dealing with the objectives of the process" the equipment required, a typical sand schedule, the calculation for frac area, fluid cleanup procedures and, finally, the advantages of combination fracturing. The areal extent of a combination fracturing treatment is discussed in the Appendix, along with fracture capacity and the fluid co-efficient for foam. Introduction One of the most significant innovations in fracturing technology in recent years -was the development of foam as a fracturing fluid in the fall of 1973. First conceived and researched by Blauer et al.(1) as a thesis project at the Colorado School of Mines, the process was quickly recognized by the oil and gas industry as a technique with a number of advantages resulting from the unique rheological properties of foam. Foam is now widely used as a fracturing fluid, for stimulating productivity of oil and gas wells, with a high ratio of success.(2,3) "Combination Fracturing" was first introduced in February of 1977 as a further improvement of the Blauer form frac process, incorporating the best features of both foam and conventional fluid fracturing treatments in one job. Results of jobs performed to date indicate that Combination Fracs achieve equal or higher productivity increases than either foam fracs or fluid fracs alone. Description of the Process A Combination Frac is actually two different fracturing operations conducted in sequence on a' well first a foam frac, followed by a fluid fracture treatment. These two fracs are continuous, with transition from one type of operation to the other effected by increasing the pumping rates of the liquid and at the same time reducing the rate of the gas volumes pumped. The first stage of a Combination Frac is generated by treated fluids and a specific N2 ratio to develop 75% quality foam at bottom-hole conditions. The foam is injected into the well as the base fluid of the fracturing treatment, with sand being added at concentrations of 1 to 2 pounds/gallon of foam. The rheological properties of foam, including its excellent sand carrying properties and low fluid loss, are such that it develops a fracture of considerable areal extent reaching deep into the formation. In the second stage of a Combination Frac, the aeration and the foaming agent ratios are reduced. Simultaneously, the pumping rate is increased and sand ratios are increased to concentrations as high as 8 to 10 pounds per gallon. The increased viscosity of this fluid stage, combined with the increased rate, develops a greater crack width. This widening of the fracture, as? described in the Appendix, results in a higher flow capacity over the total frac area developed by the treatment. Objective of a Combination Frac The productivity of a well following fracturing is proportional to both the permeability contrast (flow capacity of the fracture in md-ft divided by the flow capacity of the formation in md-ft) and the extent of the fracture area, as illustrated in Figure I.