Study of the Anti-Dilution Properties of a Special Viscoelastic Gel Applied in Severe Lost Circulation Control

Abstract

The special viscoelastic gel has been successfully applied to deal with severe lost circulation problem in more than thirty wells. It was demonstrated that the viscoelastic gel exerted important functions in dealing with the underground blowout-loss circulation coexistence problem in Shuangmiao Well 1, and the high H2S content blowout-loss circulation coexistence problem in Luojia Well 2, and high CO2 content blowout-loss circulation coexistence problem in Xushen-8 well H1. One of the important reasons why the gel was applied to deal with the problems successfully was that the gel has strong anti-dilution ability. The strong anti-dilution ability of the gel is one of the important reasons why to plugging successfully. This paper studied the heat of solution of the polymer ZND and heat of dilution of the gel-ZND based on thermodynamics. The smaller the heat of dilution is, the stronger anti-dilution ability of the gel ZND has. Chose the volume change rate through screening out to characterize the anti-dilution property of the gel and investigated the affecting factors. The experimental results showed that the quantity of screen residue decreased with the increasing of temperature, shear rate and shear time，but increased with increasing of concentration. Studied anti-dilution ability of gel-ZND in the fragmentized zone simulated by a large size plugging device. The displaced volume rates of gel-ZND with concentration above 1.0% displaced by equivalent pore volume water are all smaller than 16%. The displaced volume rate of the gel was less than 2% continuing displaced by the gel-ZND by two times pore volume water when water breakthrough came. It validated that the special gel-ZND had strong anti-dilution ability. The results provide experimental basis and theoretical guidance for resolving the potential safety hazard caused by severe loss circulation or blowout-loss circulation coexistence.