Wellbore cleaning technologies for shale-gas horizontal wells: Difficulties and countermeasures

Abstract

The application of horizontal well drilling and large-scale sand fracturing can secure an increased production in shale gas reservoirs despite of frequent gas wellbore blockage. It is vital to remove the residual bridge plug debris and sand in wellbore cleaning operation and to ensure an unblocked downhole production channel of shale gas well for a safe and smooth production process. In this paper, the current situations of the wellbore cleaning technology for horizontal wells were analyzed, and the technical challenges in wellbore cleaning treatment of shale gas horizontal wells were summarized. Based on global development of wellbore cleaning technologies for horizontal wells, technical researches were carried out on cleaning tools & technologies and working fluid performance, and cleaning treatment tools were studied and developed. Besides, technical measures of cleaning treatment were put forward and their field application effects were analyzed. Results reveal that the milling–fishing integrated tool, developed to treat large bore bridge plug, is capable of washing-over and fishing out large bore bridge plug in one trip after running in the hole; for long horizontal sections where reverse cyclone sand-washing tool is applied, the tool can prevent sand from settling so as to flush sand out of the wellbore; for normal-pressure and high-pressure wells, gas well backflow fluid, KCl and CaCl2 solution may serve as working fluid, while for low pressure wells, foam fluid can be used; for low-pressure wells, the negative pressure fishing tool is designed and optimized to drive debris or sediment into the tool through forming local negative pressure adsorption, thus complete the fishing operation. In conclusion, the new wellbore cleaning technology, which suits shale-gas horizontal wells, has laid the groundwork for large-scale wellbore cleaning treatment of shale gas wells.