Nanocomposite gel of high-strength and degradability for temporary plugging in ultralow-pressure fracture reservoirs

Gel is widely used as a temporary plugging system for well workover in petroleum engineering. This paper developed on a novel nanocomposite gel of high-strength and degradability, and researched on the factors such as monomer acrylamide, initiator Ammonium persulfate, crosslinker N,N'-Methylene diacrylamide and the temperature that could affect its gelation and mechanical properties as well as the bearing capacity of this gel system. The experiments results showed that this nanocomposite gel system could gelate (fully solidified) within 20 to 50 min under the temperature 75 degrees C to 105 degrees C, which is beneficial for fast plugging the formation with fractures. Compared with the gel system without nano-silica, the compression resistance of the system with 5% nano-silica raised from 8.7KPa to 21KPa. On the other hand, rheological measurements indicate that the nanocomposite gel initial solution has low viscosity (2.24 mPa.s, 5% nano-silica system), proving that this system easy to be pumped and a good performance of shearing resistance. The bearing capacity experiments present that for cores with fracture widths ranging from 0.398 to 0.170 cm, the bearing pressure reaches 13MPa to 20.5MPa and the fluid losses are respectively 2.5ml/5min and 7.5ml/5min at 25MPa, indicating that this nanocomposite gel has a good performance of bearing high pressure and low fluid loss. Degradability results show that the nanocomposite gel can be effectively degraded by ammonium persulfate solution and hydrochloric acid. Results of the permeability recovery test demonstrate that the core permeability damage ratio can be higher than 83%. This paper provide a new method for fluid loss control during well completion & workover in ultralow-pressure fracture reservoirs.