The Advantages of High Proppant Concentration in Fracture Stimulation

Abstract

There are several advantages to using high concentrations of proppant. For example, increasing the concentration in the fracture promotes greater fracture flow capacity, lessens sand crushing, and increases the proppant system's tolerance to fines. High flow capacity proppant systems may also result in longer sustained production increases. Introduction Since the first commercial hydraulic fracturing treatment in 1949, more than 500,000 hydraulic fracturing treatments have been conducted. The trends of fluid volume, quantity of sand, and sand concentration used in hydraulic fracturing in the U. S. over the years are shown in Fig. 1. The sand concentration has remained relatively constant, varying from 0.5 to 1.5 lb/gal, but the total quantity of sand and fluid has been on a general increase. The proppant concentration used in the fracturing treatment is important as related to the production increase resulting from the treatment. There are two proppant concentrations to be considered:(1)the proppant concentrations to be considered:(1)the pounds per gallon at the pumps (concentration at the pounds per gallon at the pumps (concentration at the surface), and(2)the pounds per square foot of fracture surface area in the fracture. The proppant concentration at the pump should be evaluated differently for a conventional fluid than for an extremely viscous fluid. For the work presented in this paper, a conventional fluid will be defined as a low-viscosity fracturing fluid in which the proppant settles from the fluid during treatment and builds up a packed proppant system. An extremely viscous fracturing fluid will be defined as one in which the proppant is suspended and does not settle during or proppant is suspended and does not settle during or following the treatment. This discussion will be limited to vertical fracture systems. Proppant Concentration in a Conventional Proppant Concentration in a Conventional Fracturing Fluid In a conventional fracturing fluid in which the propping agent settles from the fluid and packs the propping agent settles from the fluid and packs the bottom of the fracture, the proppant concentration in the fracture (lb/sq ft) would be dependent only upon the fracture width. This statement neglects the effect of higher proppant concentration on the increase in total injected volume. For larger volumes, greater fracture widths would be expected. Based upon sand weighing 100 lb/cu ft (bulk), the sand concentration in the fracture may be calculated: (1) Concentration  ( lb / sq ft )   =  100 lb / cu ft x fracture width  ( ft ) As shown in Fig. 2, to attain higher concentrations in the fracture, the fracture width must be increased. Fracture widths may be calculated from published equations. These equations indicate that the fracture width is dependent upon the fracturing fluid viscosity, injection rate, fracture length, etc. To consider the advantages of higher proppant concentrations at the pump in a conventional fracturing fluid, we must consider proppant transport in a vertical fracture. Using published equations!,' and design manuals, we can calculate proppant distribution i.e., propped fracture length and propped fracture height in propped fracture length and propped fracture height in a vertical fracture. The distribution may be evaluated from a given set of treatment variables. Example design calculations are shown in Table 1 for conventional as well as proppant-suspending fracturing fluids. As the calculations for a conventional fracturing fluid indicate, the propped fracture length and fracture width are independent of the proppant concentration at the pump or the total weight of proppant. proppant. JPT P. 643