Hydraulic Fracturing with the Single-Point Entry Technique

Introduction

Hydraulic fracturing is now in its second decade as one of the most useful techniques developed for well stimulation. As fracturing became an established practice in the oil industry, the necessary experience was gained from which advancements in fracturing technology could be made. Today, some wells are treated with fluid volumes exceeding 100,000 gal and at rates approaching 100 bbl/min Fracturing fluids are compounded for the particular formation to be fractured. Treatments are now designed with a certain degree of accuracy for a given formation area to be exposed to the fracture. These and other advances in fracturing technology have been well-received by the industry and used to advantage. Even with these improvements, however, conventional fracturing has failed to effectively stimulate wells completed in some formations. A number of the failures can be attributed to inadequate capacity of the fractures.

Formation Capacity-Fracture Capacity

Formation capacity may be defined as the product of the permeability (horizontal) of the formation times the thickness of the productive zone. Likewise, the fracture capacity is the product of the permeability of the fracture times its width. For best results in well stimulation, the fracture capacity should be at least 10 times the formation capacity.

Conventional fracturing usually results in fractures having capacities of a few hundred to a few thousand millidarcy-feet. Fractures with capacities in this range are usually adequate for stimulation in zones of low permeability and/or small thickness. For example, a zone of 40 ft in thickness with a permeability of 5 md has a capacity of 200 md-ft, and a well completed in this zone should be stimulated effectively with a fracture of 2,000 md-ft capacity. This capacity fracture can often be obtained by conventional fracturing, provided the fracture is propped effectively.