Chemical Analysis of Flowback Water and Downhole Gas-Shale Samples

Topics: Reservoir characterization Tight gas/shale gas/coalbed methane Water treatment and management
Getty Images

Recently, flowback chemical analysis has been considered to be a complementary approach for evaluating fracturing operations and characterizing reservoir properties. Understanding the source of flowback salts and the mechanisms controlling the water chemistry is essential but also challenging because of the complexity of water/shale interactions. In this study, samples of flowback water and downhole shales are analyzed to investigate the mechanisms controlling the chemistry of flowback water.

Introduction

Field data show that chemistry of flowback water is substantially different from that of the injected water. For instance, in the Horn River Basin (HRB), slick­water (with salinity levels similar to those of fresh water) is injected into the reservoir to create fractures, while the recovered flowback water is highly saline (40,000–70,000 ppm).

Analysis of flowback data from the HRB wells indicates that the shape of the salt-concentration profiles is related to the fracture-network complexity. Knowledge of flowback-water composition is also required for water environmental assessment and selection of appropriate remediation strategies.

Although flowback chemical analysis has been used widely to assess fracturing operations, the source of the ions in the flowback water is still a matter of debate. This study analyzes the flowback water and the shale samples to investigate the source of the ions and factors controlling flowback-water chemistry. Intact flowback-water samples are digested in acid to dissolve the precipitated salts and possible colloidal particles. A comparative analysis of the intact and acid-­digested flowback-water samples is performed for better understanding of the mechanisms affecting flowback-­water chemistry. The intact flowback-water samples are evaporated, and the remaining salts are investigated with X-ray diffraction (XRD) and scanning electron microscopy with energy-­dispersive X-ray spectroscopy (SEM-EDXS). Furthermore, a ­sequential-ion-extraction method is developed to identify the loosely, moderately, and strongly attached ions.

This article, written by Special Publications Editor Adam Wilson, contains highlights of paper SPE 175925, “Chemical Analysis of Flowback Water and Downhole Gas-Shale Samples,” by Ashkan Zolfaghari, SPE, Yingzhe Tang, Jordan Holyk, Mojtaba Binazadeh, and Hassan Dehghanpour, SPE, University of Alberta, and Doug Bearinger, SPE, Nexen Energy, prepared for the 2015 SPE/CSUR Unconventional Resources Conference, Calgary, 20–22 October. The paper has not been peer reviewed.
...
This article is reserved for SPE members and JPT subscribers.
If you would like to continue reading,
please Sign In, JOIN SPE or Subscribe to JPT

Chemical Analysis of Flowback Water and Downhole Gas-Shale Samples

06 August 2016

Volume: 68 | Issue: 9