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

摘要

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.