Abstract
Lost circulation is a common problem in drilling project, especially the severe loss which consumes much material and costs much time, sometimes induced wellbore collapse, drill pipe sticking, overflow, blowout and well abandon at last. Based on theory of structure liquid, supramolecular chemistry, water-solubility salt-resisting and temperature-resisting polymer, we designed and synthesized the gel, called special gel, which is used to control severe lost circulation. When dispersed in water, a reversible supramolecular structure (dynamic physical cross-linking network) developed, which rendered the dispersion some special characteristics.
This paper investigates the rheology of the gel which is accordance with pseudoplastic fluid with yield point. The gel has thixotropy, good tackifying effect and shear-thinning behavior, and visible viscoelasticity. Those rheology characteristics show the gel has the potential to plug the weak zone. The gel is hard to be dilute by formation fluids for its apparent viscosity and strong cohesive force. Its shear-thinning property can provide the gel be pumped and flow in pipes easily, and flow with high viscosity and resistance in the zone porous. And its visoelasticity make the gel has high flood efficiency to cut off the connection between the formation fluid and the drilling fluid in borehole. It will impose a higher pressure to push the gel system after the gel stay. And the gel has good Compatibility with common use lost circulation materials such as walnut shell, cement. When the loss pressure difference is too high, the gel can be used with bridge plug or cement. The gel is benefit to control severe lost circulation accompanying with water zones or overflow and loss coexist. The gel was successful to deal with severe loss in Sichuan, Changqin and Tuha oil fields in China.
