The disclosure herein relates to crosslinkable polymers for use in downhole applications such as drilling and completion operations.
Many subterranean treatments require viscosified fluids. For instance, viscosified fluids may be used as or in drilling fluids, completion fluids, as well as other treating fluids. The term “drilling fluid” as used herein refers to any of a number of liquid and gaseous fluids and mixtures of fluids and solids (as solid suspensions, mixtures and emulsions of liquids, gases and solids) used in operations to drill boreholes into the earth. In some embodiments, a completion fluid may be used to control a well should downhole hardware fail, without damaging the producing formation or completion components. Such viscosified fluids can also be used to stave off the loss of fluids from the well bore to the surrounding formation, for example, when a kick or a thief zone is encountered.
Naturally-derived polymeric viscosifying agents, such as cellulose derivatives, are often preferred over some synthetic agents because of their relative cost. But this cost savings is of little value if the viscosifying agent cannot maintain sufficient viscosity. Maintaining viscosity in a drilling fluid, for example, is important to provide hydrostatic pressure to prevent formation fluids from entering into the well bore, keep the drill bit cool and clean during drilling, carry out drill cuttings, and suspend the drill cuttings while drilling is paused and when the drilling assembly is brought in and out of the hole. Maintaining sufficient viscosity also may be important to control and/or reduce fluid loss into the formation. Moreover, a treatment fluid of a sufficient viscosity may be used to divert the flow of fluids present within a subterranean formation (e.g., formation fluids, other treatment fluids) to other portions of the formation, for example, by “plugging” an open space within the formation. At the same time, while maintaining sufficient viscosity of the treatment fluid often is desirable, it also may be desirable to maintain the viscosity of the treatment fluid in such a way that the viscosity may be reduced at a desired time, inter alia, for subsequent recovery of the fluid from the formation.
Further complicating the use of some cellulose derivatives is that they are generally not viewed as thermally stable and easily solubilized. Furthermore, to provide sufficient viscosity, oftentimes cellulosic polymers are crosslinked using metal ions such as zirconium and titanium through techniques well known in the art. Unfortunately, however, the subterranean treatment fluids made with the resulting metal-crosslinked cellulosic polymers are not re-healable, meaning that the viscosity of these fluids degrades irreversibly under shearing and, therefore, is not resilient in drilling operations or other downhole operations that involve changes in shear.