Method for Estimating and Analyzing for TOC of Hydraulic Fracturing Fluids

Abstract

Total Organic Carbon (TOC) is a characteristic of the amount of organic carbon present in a chemical compound or mixture, such as a hydrocarbon-bearing formation, water, or even a fracturing fluid. Organic carbon is a potential measure of food available for bacteria, and, as such, an indirect measure for the potential for wellbore fouling, formation damage, and regained permeability. For this reason, TOC is often used as an indicator of overall water quality across multiple industries, and is becoming more prevalent as a general indicator of water quality for frac reuse. TOC has been demonstrated to be directly correlative to the much-more difficult and time-dependent determination of Biochemical Oxygen Demand (BOD), and a recently developed method by which TOC can be analyzed in the field has made TOC determinations even more accessible. The paper provides a theoretical determination of the TOC of over 100 fracturing fluid additives and compares the results with a field method for making TOC determinations. Also provided are examples on how to use TOC values for individual stimulation fluid additives to estimate the TOC of the entire frac fluid as pumped. The result of the exercise in assessing the TOC content of various slickwater and crosslinked polymer fluids provides a comparative guide for potential downhole bacterial and formation damage issues. It is therefore possible to estimate the potential for proppant pack and/or formation damage with knowledge of the TOC of a fracturing fluid prior to its selection without having to resort to an analysis of the fluid. Also provided are insight into the range of TOC's that might be observed in various spent frac flowback waters as they are associated with general frac fluid types, such as Slickwater or Crosslinked frac fluids. Armed with knowledge of the TOC of actual flowback it may be possible to determine whether or not additional well cleanout operations might improve well productivity.