Paper: New Type Selective Sequestrant For CrossLinked Fracturing Fluids Controls Iron In The Permian Fort Worth Basins

A research project was undertaken to develop an iron sequestering agent which could be used to control the precipitation of iron in fracturing operations without affecting the rheological properties of the crosslinked gel. The control of iron in production comes in combine and can cause acidizing is well documented but it has only recently been recognized as a problem in fracturing. Problems occur when oxygen in the fracturing fluid contact with iron in solution in the formation water. The two components if conditions permit an insoluble precipitant will form. This precipitate severe permeability damage. In acidizing, sequestrants have been widely used for years to control iron. However, when fracturing with crosslinked fluids these same sequestrants will complex with the gel crosslinker as well as with iron. This reaction will prevent the fracturing fluid from crosslinking. Recently, a new selective sequestrant was developed which reacts only with iron and therefore does not affect the rheology of the crosslinked gel. This paper describes the problems associated with fracturing formations containing high amounts of in-situ iron and the manner in which this new selective sequestering agent can be used to prevent these problems. Rheology data will be presented to show the compatibility of the sequestering agent with the crosslinked gel system which was specifically designed to be used with the new sequestrant. Finally, its effectiveness as an iron control agent is demonstrated through lab flow tests and field case histories in which the compound was used.