Thirty Years of Gas Shale Fracturing: What Have We Learned?

Abstract

Although high gas flow rates from shales are a relatively recent phenomenon, the knowledge bases of shale-specific well completions, fracturing and shale well operations have actually been growing for more than three decades and shale gas production reaches back almost one hundred ninety years.   During the last decade of gas shale development, projected recovery of shale gas-in-place has increased from about 2% to estimates of about 50%; mainly through the development and adaptation of technologies to fit shale gas developments. Adapting technologies, including multi-stage fracturing of horizontal wells, slickwater fluids with minimum viscosity and simultaneous fracturing, have evolved to increase formation-face contact of the fracture system into the range of 9.2 million m² (100 million ft²) in a very localized area of the reservoir by opening natural fractures.  These technologies have made possible development of enormous gas reserves that were completely unavailable only a few years ago.  Current and next generation technologies promise even more energy availability with advances in hybrid fracs, fracture complexity, fracture flow stability and methods of re-using water used in fracturing.  This work surveyed over 350 shale completion, fracturing and operations publications, linking geosciences and engineering information together to relay learnings that will identify both intriguing information on selective opening and stabilizing of micro-fracture systems within the shales and new fields of endeavor needed to achieve the next level of shale development advancement. 

Introduction

The first lessons from this study are:

• No two shales are alike.  Shales vary aerially and vertically within a trend, even along the wellbore.
• Shale "fabric?? differences, combined with in-situ stresses and geologic changes are often sufficient to require stimulation changes within a single well to obtain best recovery. 
• Understanding and predicting shale well performance requires identification of a critical data set that must be collected to enable optimization of the completion and stimulation design.
•  There are no optimum, one-size-fits-all completion or stimulation designs for shale wells.

Although gas shale completions literature is developing rapidly, the history of gas shale research offers a starting point that can help explain many phenomena seen in shales world-wide.  To this point, many of the efforts in gas shale developments have been sheltered within a handful of companies that have pushed their own gas-shale learning envelopes as a competitive advantage.   There are, however, many solid advances in shale that have been reported in the technical literature. Of the 350+ references reviewed for this report and the 250 included, >60% have been written in the last 36 months and learnings are increasing rapidly. This paper seeks to report and define many of these advances. Information from SPE, AAPG, consultant reports, academic and government work have been reviewed to establish a history of what we, as an industry, have done and hopefully provide commentary on what enabling technologies need to be developed and refined.  In this spirit, discussion on geology, geochemistry and seismic have been briefly reported to lay a foundation for the fracturing discussion.