Improved Method to Evaluate Flowback Additives for Frac Fluids Used in Unconventional Reservoirs

Abstract

Productivity of unconventional low permeability sandstone formations and shale plays can be adversely affected by invasion of frac fluid filtrate from hydraulic fracturing treatments. The filtrate can increase water saturation in the pore system when it is not fully recovered upon production of the well decreasing effective permeability. Civan discusses this type of formation damage extensively (Civan 2014). A number of additives for frac fluid systems have been introduced to aid in filtrate recovery, speed turnaround time and improve production after stimulation. Gravity drainage column tests (GDCT) using ground rock or drill cuttings have been introduced to evaluate these products. The test offers the advantage of rapid evaluation of hydrocarbon displacement of simulated invaded, frac fluid filtrate. However, the test has limitations of pressure and temperature such that it cannot fully evaluate a products ability to displace bound water on the rock surfaces. A flow test method has been developed to improve on the GDCT. The test is conducted at reservoir temperature with elevated pore pressure using either ground formation material or plugs of recovered reservoir core. The test provides a compromise between the need for quick turnaround time for product selection and a more rigorous, time consuming flow study with volume displacement measurements and fluid saturation calculations. Comparison of results from GDCT and the new method are given.

Nonionic and anionic surfactants as flowback aids in hydraulic fracturing methods of crude oil production

“…Surfactants may be added to enhance flowback by altering rock wettability as well as reducing fluid surface tension and associated capillary pressure (Hussien et al, 2019). Their utility in unconventional and tight reservoirs has been the subject of much research given the narrow pore throats and low permeability characteristics of these formations, which cause high capillary pressure, impeding oil flow (Alvarez et al, 2014; Issac et al, 2022; Gupta et al, 2020; Himes et al, 2017; Liang et al, 2015; Omari et al, 2021).…”

“…The objective of this work was a systematic evaluation of series of nonionic and anionic surfactants which have utility as flowback aids in hydraulic fracturing. The surfactants studied were evaluated as flowback enhancers in simple gravity drainage tests, described herein and featured by various researchers in past works (Galindo & Rimassa, 2013; Himes et al, 2017; Penny et al, 2012; Yue et al, 2016). Performance was correlated with surfactant CMC, surface tension (ST), contact angle by capillary and captive bubble measurements, relative solubility number (RSN) and hydrophilic–lipophilic balance (HLB) in an attempt to identify correlations between surfactant performance and their physical and surface properties.…”