Abstract
This paper is concerned with the effect of propping-agent concentration on flow capacity of a fracture in the case in which there is embedment of the propping agent. Previous published studies have shown definitely that there is a relationship between fracture flow capacity and propping-agent concentration, and it has been shown that the theoretical results are confirmed by laboratory experiments.
The problem of directly finding sand concentration for maximum flow capacity of a sand-propped fracture is solved, and formulas and charts are given to obtain this concentration under various conditions of effective overburden pressure, medium sand-grain diameter and rock properties. It is shown that, for the same effective overburden pressure and the same rock characteristics, optimum sand concentration in pounds per gallon does not depend on medium sand diameter. For conditions met in hydraulic fracturing operations, it is found that sand concentration in grains per square inch for maximum flow capacity varies within a wide range of values; this indicates the convenience of using data of fracturing pressure and rock characteristics for calculating sand concentration in order to achieve the best results in fracture treatments.
Introduction
It has been pointed out in the published literature that one important factor controls the success of a hydraulic fracturing operation - the propping of the fracture. The main effect of the propping agent is to hold the fracture open by means of the reaction forces that oppose the pressure due to the overburden. It is assumed in this paper that the propping agent is sand, that the grains are spherical and uniform in size, and that this sand is distributed in a monolayer in the fracture.
The existence of a sand concentration value for maximum fracture flow capacity has been recognized since the publication of one of the first studies on the subject. In the reference cited, flow capacity was assumed to be proportional to the cube of the fracture volume per square inch not filled by sand.
Study on shear fracture flow capacity of hard brittle rocks
