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Exploration • Drilling • Field Services


Responsible chemical development is required for fracture application


Jonathan J Wylde on a chemical additive used in hydraulic fracturing. H


ydraulic fracturing involves breaking subterranean rock with hydraulic pressure in order to create higher permeability for hydrocarbon fluids and gas through the wellbore.


To keep the fractures open, ceramic proppant (or sand) is pumped as slurry into the fracture. Recent advances in fracturing technology have allowed for the economic production of unconventional gas deposits such as shale gas and coal bed methane. Chemical additives are essential to the success


of hydraulic fracturing, with dozens of additives that can potentially be used in any given fracture treatment. However, the use of chemicals in fracture applications has come under increased scrutiny worldwide; particularly in North America where fracturing has become a common practice. As a result, much focus has been made on the development of environmentally-acceptable chemistries for both bespoke applications and for the replacement of potentially environmentally- hazardous chemistries currently in use. One such chemical is 2-butoxyethanol (2-BE,


EGMBE, BGE, butyl cellosolve), which forms part of the pre-flush treatment and acts as a mutual solvent.


Parameter EC50 – Skeletenema Costatum


EC90 – Skeletenema Costatum NOEC


LC50 – Acartia Tonsa


LC90/LC100 – Acartia Tonsa NOEC


LC50 – Cyprinodon Variegates


LC90/LC100 – Cyprinodon Variegates NOEC


LC50 – Corophium Volulator NOEC – Corophium Volulator


Bioaccumulation – OECD 117 Biodegradation – OECD 306


Weighted Log POW


74% 14 days 77% 21 days 74% 28 days


= 1.84


Use of this chemistry can provide significant benefit by removing water blocks, preventing emulsion formation and allowing better flowback of the fracture treatment and therefore faster well clean up. Yet like many chemicals, the use of 2-BE has come under scrutiny primarily due to toxicity concerns. Experimental studies are available and report that high exposure has allegedly caused birth defects and that ingestion can cause breathing problems, low blood pressure, lowered levels of hemoglobin, blood in the urine and metabolic acidosis (Harris et al., 1998). Te key environmental test parameters for 2-BE are summarised in Table 1 – it can be generally summarised that while it is a readily biodegradable compound, it is able to bioaccumulate and is toxic. Clariant Oil Services initiated an intense R&D


programme aimed to identify a replacement for 2-BE, with superior environmental performance while maintaining the desirable features this chemistry offers during fracturing and flowback. Te final product was chosen for its mutual solvency and wettability modification properties. Te VES-based fracture additive package, when


untreated, formed an emulsion with condensate, commonly produced alongside gas in shale


Table 1. Key to environmental parameters 2-butoxyethanol


24.2 mg/L 24 hours 18.1 mg/L 48 hours 21.8 mg/L 72 hours 45.3 mg/L 72 hours 10.0 mg/L 72 hours


175.5 mg/L 24 hours io8.8 mg/L 48 hours 182.7 / 182.7 mg/L 48 hours 35.6 mg/L


>300 mg/L 24 hours >300 mg/L 48 hours >300 mg/L 72 hours >300 mg/L 96 hours >300 / >300 mg/L 96 hours 300 mg/L 96 hours


Replacement Chemistry


600 mg/L 24 hours 870 mg/L 48 hours 993 mg/L 72 hours 1512 mg/L 72 hours 560 mg/L 72 hours


>2200 mg/L 24 hours 1273 mg/L 48 hours >2200 / 2200 mg/L 48 hours 81.4 mg/L


>300 mg/L 24 hours >300 mg/L 48 hours >300 mg/L 72 hours >300 mg/L 96 hours >300 / >300 mg/L 96 hours 300 mg/L 96 hours


5740 mg/kg 10 days 1729 mg/kg 10 days


Not a suitable test for surficants


76% 14 days 77% 21 days 79% 28 days


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