This paper describes the methodology and results of a series of tests conducted on HydroxyEthyl Cellulose (HEC) gel to determine its effects on return permeability. HEC gel is widely used in the oilfield as a carrier fluid in gravel packing operations and is generally considered to cause minimal formation damage. However, results of this study indicate that even when HEC gel is efficiently removed from the formation, interaction between the fluid and the formation can result in reduced return permeability. Therefore, particular care must be given to quality control and mixing procedures to minimize potential formation damage.
HEC gel break-back procedures used by oilfield laboratories for return permeability measurement are based on displacement studies related to reservoir engineering. In these tests, flow through a Berea core is maintained at constant pressure and later, after introduction of the test fluid, the change in permeability is calculated as a percent of the initial permeability. In these cases, any resulting loss of permeability was assumed to be caused by HEC gel trapped in the formation.
To insure complete HEC degradation over time and temperature with and without the presence of formation minerals, seven different breaker systems were evaluated to select the most efficient system.
This study concludes that damage caused by HEC residue is minimal compared to the damage caused by the interaction of the fluid and the rock minerals present in various formations. The results of our investigation also indicate that the performance of breakers is influenced by the presence of formation minerals.
This paper will present experimental data of HEC gel break-back in the presence of formation minerals as well as the testing of chemical additives designed to minimize damage and deliver improved return permeability.