Critical Evaluation of Additives Used in Shale Slickwater Fractures
Authors: Bybee Karen 
Published: February 2015

This article, written by Assistant Technology Editor Karen Bybee, contains highlights of paper SPE 119900, "Crit ical Evaluations of Additives Used in Shale Slickwater Fracs," by P. Kaufman, SPE, and G.S. Penny, SPE, CESI Chemical, and J. Paktinat, SPE, Universal Well Services, originally prepared for the 2008 SPE Shale Gas Production Conference, Fort Worth, Texas, 16-18 November. The paper has not been peer reviewed.
Slickwater fracturing has increased over the past decade, with the advent of shale gas plays. Horizontal wells are now the standard, with as much as 1 million gal of water in as many as six to nine fracture stages per well. The objective is to create as much contact with the reservoir as possible. Additive packages have been minimized to reduce costs. Because of environmental concerns and freshwater availability, the flowback and produced water are collected and used for subsequent fracture treatments. The full-length paper examines water-treatment techniques and evaluates the performance of additives that are used in slickwater fractures of shale reservoirs.

Introduction
The number of slickwater fractures has increased because of higher natural-gas prices and more experience in fracturing with lower-cost fluids. Slickwater fractures have been used in low-permeability and large net pays, and they require large amounts of water to obtain adequate fracture half-lengths. Before the Barnett shale in north Texas was fractured in 1997, many fractures were carried out with a crosslinked fluid and large amounts of proppants. The difficulty in cleaning up the wells and the low return made many wells uneconomical. Some wells were treated with slickwater and no proppant. Initial production was higher but declined rapidly. Eventually, the state of the art evolved to high-rate slickwater fractures with various additives. The question to be addressed is how the various additives perform in shale and how to determine which additives are necessary, particularly in light of the fact that most fractures are now conducted with produced and/or flowback water from previous fractures.

Water Reuse
Water can be reused and makes up the majority of volume in a slickwater fracture. There have been and are problems in obtaining sufficient water from municipalities or disposing of produced water. If there is a way to reuse the water or fluid, this will save money and solve environmental issues with disposal. Disposal costs can run as high as USD11/bbl. With the advent of horizontal wells with multiple staged fractures, there is a process requirement as great as 10,000 B/D with the entire job requiring as much as 100,000 bbl of water. Surface waters alone can contain clays, sand/silt, iron, sulfates, and bacteria. Produced water and reused fracture waters can have various contaminants.
The presence of the many possible contaminants can affect the performance of the fracturing-fluid additives. For example, surfactants and clay stabilizers can be adsorbed onto the colloidal solids. The presence of solids, residual gel, and bacteria also can impair formation permeability.