Abstract
Borate or Group 4 metal-crosslinked biopolymer fluids constitute the bulk of gelled fracturing fluid volumes used in field fracture stimulation operations to date. Oxidizing chemicals remain the primary gel breakers to breakdown the filter cake and establish regained formation or fracture conductivity. These breakers presumably oxidize the polymer backbone, causing chain breakdown, thereby facilitating fluid flowback. Safety hazards associated with using bulk quantities are one of the many potential problems associated with the use of oxidizing agents as gel breakers. Proper timing of gel breakdown is of utmost importance with respect to oxidizing gel breakers. Conversely, premature polymer oxidation can cause premature proppant settling. On the other hand, a long delay between the completion of the fracturing operation and activation of the gel breaker could cause deposition of additional filtercake on fracture faces, which could be difficult to break down. A desirable advancement of designing improved fracturing fluids is to develop non-oxidizing gel breakers that focus on decrosslinking the crosslinked gel structure by reacting with the crosslinking agent, rather than only breaking down the polymer chain. Additionally, by insolubilizing such breakers, they can be embedded in the filter cake and, on activation, they can degrade the filter cake completely without leaving any residues.
This paper begins by examining a study on filter cake characterization using zirconium-crosslinked fracture fluids. The filter cake was formed by flowing, under pressure, crosslinked fluid through synthetic aloxite discs of different porosities. Results from the evaluation of relationships between permeability/porosity of the discs, filter cake thickness, and filter cake polymer concentration are presented. Next, laboratory development and screening of some non-oxidizer type chemical gel breakers that can actively decrosslink zirconium at formation temperatures are discussed. Finally, the paper discusses some insolubilized breakers that become embedded in the filter cake and break it down from within.
