Gelled liquid hydrocarbon treatment fluids having reduced phosphorus volatility and their associated methods of use and preparation

#This invention relates to reduced volatility gelled liquid hydrocarbon treatment fluids and methods of their use and preparation.

#Gelled liquid hydrocarbon fluids have been utilized in treating subterranean formations penetrated by well bores, e.g., for stimulation or sand control treatments such as fracturing or gravel packing, respectively. In fracturing treatments, a gelled liquid hydrocarbon fracturing fluid that may comprise particulates, often referred to as proppant, suspended therein is pumped through a well bore into a subterranean formation at a rate and pressure such that one or more fractures are formed or enhanced in a portion of the formation. Proppant particulates may be deposited in the fractures, inter alia, to prevent the formed fractures from closing, thereby maintaining conductive channels through which produced fluids can flow to the well bore. At a desired time, the viscosity of the gelled liquid hydrocarbon fluid may be reduced, or “broken,” and the fluid may be recovered.

#Similarly, sand control operations, such as gravel packing, use gelled liquid hydrocarbon fluids, often referred to as gravel pack fluids. Gravel pack fluids usually are used to suspend gravel particulates for delivery to a desired area in a well bore, e.g., near unconsolidated or weakly consolidated formation particulates, to form a gravel pack to enhance sand control. One common type of gravel packing operation involves placing a gravel pack screen in the well bore and packing the annulus between the screen and the well bore with gravel of a specific size designed to prevent the passage of formation sand. The gravel, inter alia, acts to prevent the particulates from occluding the screen or migrating with the produced fluids, and the screen, inter alia, acts to prevent the gravel from entering the production tubing. Once the gravel pack is substantially in place, the viscosity of the gravel pack fluid often is reduced to allow it to be recovered or produced back from the well bore.

#This invention relates to reduced volatility gelled liquid hydrocarbon treatment fluids and methods of their use and preparation.

#When conventional phosphoric acid ester gelling agents are manufactured, they contain certain amounts of monoesters and diesters of orthophosphoric acids. See Hochwalt et al., Alkyl Esters of Phosphoric Acid, IND. AND ENG'G CHEMISTRY, Vol. 34, at 20 (1942). These diesters are desirable, in that they are useful for gelling liquid hydrocarbons. The monoesters, on the other hand, are not useful for gelling liquid hydrocarbons and may be problematic. Conventional phosphoric acid ester gelling agents have proven to have very little utility for gelling liquid hydrocarbons due to their high monoester concentrations. To counteract the potential problems presented by the monoesters, over the last thirty years or so, trialkyl phosphates (e.g., triethyl phosphate) have been included to improve the yield of the diesters. See U.S. Pat. No. 4,537,700, regarding, inter alia, a discussion of the addition of triethyl phosphate to improve the yield of the diesters.

#In this invention, it has been recognized that residual trialkyl phosphates, such as triethyl phosphate, may actually be the source of the volatility problems in downstream processing operations that are commonly associated with conventional phosphoric acid ester gelling agents (as opposed to the general wisdom that the volatility problems are associated with their alleged lack of stability). Residual trialkyl phosphates are problematic because of their vapor pressure, which allows them to vaporize at the temperatures used in downstream processes, which can lead to fouling. The following table helps illustrate this point.