Resin-coated proppants improve well stimulation results by preventing flowback, or fracture evacuation, near the wellbore, a phenomenon that effectively "decouples" the wellbore and the productive formation. in addition, the deformable coating protects the resin-coated proppants from crushing and helps resist embedment in softer formations. The tough coating is chemically inert in crude oils, brines, and most acids. The resin-coated materials work best under actual downhole conditions since the closure stress and temperature help lock the materials in the fracture for the life of the well.
This paper reviews case histories from four wells in which resin-coated proppants were used. In addition, simple lab tests of the resin-coated proppants in an API crush cell confirm their excellent properties and potential. Together, these results show the need for potential. Together, these results show the need for resin-coated proppants in many types of wells. In many ways they act as "ideal" proppants that can be economically justified over uncoated proppants.
Since the early years of hydraulic fracturing, many workers have recognized the potential of this form of well stimulation and have sought to improve its results. Advances in fluid systems, techniques, and equipment now provide better frac treatments. Additional improvements have been sought with new proppants. Yet today the original material used to prop proppants. Yet today the original material used to prop open fractures - sand - is still the main proppant used in most wells even though a need for better proppants is evident.
Analyses of results of fracturing, combined with laboratory investigations and field tests, have shed considerable light on the subject of proppants. We now know that high-strength materials may be required where closure stresses in hard rock are high. Deformable materials may be needed to prop soft formations. Besides sand, materials such as ceramic beads, glass beads, steel shot, and nut shells have been tested. Chemicals designed to consolidate sand have been tried. As a result of this work we can now specify that an ideal proppant is one which
* is strong,
* is deformable,
* is chemically inert,
* is cost effective,
* has low specific gravity,
* is available,
* resists flowback, and
* resists embedment.
While sand meets several of the specifications - it is strong, cost effective, and available - however, it will crush in deeper wells and tends to flow back or embed. Bauxite is stronger than sand, chemically inert, and slightly deformable, but it does flow back and can erode valves, chokes, tubular goods, and even the wellhead. In some formations its high hardness spalls rock or generates formation fines detrimental to the well's production. Bauxite's hardness causes embedment in production. Bauxite's hardness causes embedment in many formations. Its comparatively high specific gravity is a disadvantage since fewer grains are available per pound when purchased, and the carrying capacity of per pound when purchased, and the carrying capacity of the frac fluid must be quite high to transport it effectively. Finally, it is expensive.
For the past five years, resin-coated proppants that meet all of the specifications of an ideal proppant have been used throughout North America to help proppant have been used throughout North America to help improve stimulation results and solve many problems inherent to sand and bauxite proppants.