Abstract
The intention for using proppants in a fracture is to create a hydraulically conductive pathway for reservoir fluids that is open to flow and stays open. Most propped fractures, however, experience a loss of flow capacity with time. Several mechanisms have been identified that contribute to this loss, such as mechanical failure of proppant grains, proppant embedment, fluid residue damage, formation spalling, and others. Recently, fracture diagenesis has been proposed as an additional mechanism that can significantly contribute to the slow loss of fracture conductivity.
Previous attempts to quantify the degree of diagenetic activity have been made under conditions of stress and temperature, but without dynamic fluid flow. This paper presents an automated experimental setup that enables long-term (six or more months) dynamic flow testing of multiple proppants simultaneously at reservoir temperature conditions.
This apparatus was used to determine the rate of diagenetic activity on some sand and ceramic proppants with slow, continuously flowing formation water. The results are compared to static cell test results. In addition to a baseline comparison of the proppants under consideration, specialized coatings aimed at reducing the rate of diagenetic reactions are evaluated. Data for four proppants and six coatings subjected to 350°F flowing simulated formation water for six months are presented. Proppants were analyzed for changes in mechanical and compositional properties after 0, 2, and 6 months by scanning electron microscope (SEM), energy-dispersive X-ray spectroscopy (EDX), X-ray diffraction (XRD), and crush strength. Dynamic permeability was monitored periodically throughout the test period along with produced fluid ionic content as determined by inductively coupled plasma (ICP) testing. Mass changes of each test proppant were measured.
Results presented in this paper should be helpful to the stimulation engineer responsible for selecting proppants desiring sustained fracture conductivity. A detailed description of an automated laboratory method in which proppants can be evaluated for long periods of time with little human interaction is presented.
