Temporary sealing technology to control formation damage induced by drill-in fluid loss in fractured tight gas reservoir

Western Sichuan tight gas reservoir is characteristic of developed natural fractures and ultra low matrix permeability. Developed fractures are beneficial for the economic and efficient development of tight gas reservoir. But they will lead to lost circulation of drill-in fluid and induce serious formation damage. Moreover, the dynamic fracture width which can reach several hundred microns or millimeter level resulting from drill-in fluid invasion increases the difficulty to solve the problem. To our best knowledge, few papers have been published on the technology that gives a synthetic consideration to both lost circulation control and formation damage prevention in fractured tight gas reservoir. In this paper, we develop the temporary sealing technology and propose its key indexes to control drill-in loss in fractured reservoir. Laboratory experiments are conducted to determine the optimal material size, type and concentration to meet the index requirements. Maximum plugging pressure, total loss volume before sealing and permeability recovery rate are the three key indexes for the temporary sealing technology. Results of laboratory experiment considering the three indexes show that the D90 of the bridging particle size distribution should be equal to the maximum dynamic fracture width. The reasonable combination of rigid granule, fiber and elastic particle can create a synergy effect. The optimal concentration for rigid granule, fiber and elastic particle is 5.0%, 3.0% and 2.5% respectively. Based on the temporary sealing technology, the maximum plugging pressure and permeability recovery rate can be improved to 15.0 MPa and 88.6% respectively, and the total loss volume before sealing can be reduced to only 49 mL. (C) 2014 Elsevier B.V. All rights reserved.