High Temperature Sealing Performance of Novel Biodegradable Colloidal Gas Aphron (CGA) Drilling Fluid System

Aphrons are ideal sealing materials and colloidal gas aphron (CGA) drilling fluids have been successfully applied in solving huge leakage problems. As the increase of well temperature, filtration and sealing characteristics of CGA drilling fluids at high-temperature are more concerned, yet less investigated. This study revealed an easily biodegradable CGA drilling fluid system generated by modified starch polymer EST and glycine surfactants AGS-12. Its high-temperature high-pressure (HTHP) filtration performance was evaluated through API filtration test, HTHP filtration test (150-200 degrees C, 3.5 MPa), and the HTHP sand disc experiment (150 degrees C, 3.5 MPa). Results indicated that the EST-CGA is a strong sealing ability drilling fluid system with temperature resistance of 200 degrees C and pressure resistance of 3.5 MPa. It can effectively seal the reservoirs with pore-throat diameters twice the microbubbles average diameter. The optimal sealing effect can be obtained when the ratio of the centralized tendency of the mircobubbles and the average pore-throat diameter was close to 1 : 1. The great improvement in HTHP filtration performance of EST-CGA was attributed to the introduction of rigid temperature-resistant groups and hydration groups in the EST-CGA system, as well as the formation of hydrogen bonds between N-H/O-H and COO-.