Long-Term Dynamic Flow Testing of Propants

摘要

The purpose of 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, etc. 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 months or more), dynamic flow testing using multiple test cells to allow evaluation of multiple proppants simultaneously at reservoir temperature conditions, but without stress applied. This apparatus was used to determine the rate of diagenetic activity on sand and ceramic proppants with slow, continuously flowing simulated formation water. Permeability loss data for four proppants and six coated proppants subjected to 350°F flowing simulated formation water for six months are presented. Scanning electron microscope (SEM), energy- dispersive X-ray (EDX) spectroscopy, and grain strength data are presented to describe the onset of diagenesis. Dynamic permeability was monitored throughout the test period along with produced fluid ionic content as determined by inductively coupled plasma (ICP). Mass changes of each test proppant were measured. Results presented in this paper should be helpful to stimulation engineers responsible for selecting proppants for sustained fracture conductivity. It provides detailed description of an automated laboratory method in which proppants can be evaluated for long periods of time with little human interaction.