Successful stimulation of an oil or gas well by a hydraulic fracturing treatment is largely dependent on obtaining a propped fracture with adequate fracture conductivity. The fracture conductivity is influenced by the reservoir environment following a hydraulic fracturing treatment. Many years of field experience have shown that it is usually necessary to use a gelled fluid to create fracture width and suspend the proppants. However, until only recently, laboratory testing methods did not realistically measure the damaging effects of these fluid systems on the conductivity of propped fractures.
As reported in recent publications, a few laboratories have constructed large scale models to simulate the pumping operation as well as the postfrac reservoir environment of a propped fracture. During pumping, treatment conditions are simulated by using a high shear flow loop to model wellbore tubular conditions, and a low shear, heated flow loop to simulate flow down the fracture. The fluid then enters a heated test cell where dynamic fluid loss in the fracture is modeled with core wafers set apart to allow fluid to flow between them and create gel filter cakes. A proppant-laden slurry is then Injected Into the gap between the core wafers and closure stress is applied.
This completes the simulation of the fracturing treatment and the propped fracture. While holding the cell at the temperature of the reservoir being modeled, the fracture conductivity is monitored for long time periods at stress progressively increasing levels of stress.
This paper describes the equipment and procedures used to accurately simulate stimulation treatment and downhole reservoir conditions. Resultant conductivity data of both sand and manufactured proppants are presented incorporating many of the commonly used fracturing fluid systems at different reservoir conditions of temperature and stress. Data comparisons are also presented whereby fracture conductivity data was obtained with both aqueous and hydrocarbon fluids as the flowing media.