Sergei ATRUSHKEVICH, Design Manager and First Deputy Director at Novinka CJSC

Clearing of wells from drilling fluids, sand and other mechanical impurities during their construction and operation is comming into sharp focus. Now two main methods of cleaning wells are widespread: washout and using bailers. But often the application of these methods does not bring the desired results (for example, in wells with abnormally low reservoir pressures and high liquid uptake or in wells with extended horizontal sections). To work in such conditions, ejector cleanout technology can be successfully applied.

The technology of well ejector cleanout is based on the ejection effect created by a flow having a high flow velocity (jet pump). For circulation, a double (concentric) coiled tubing is used, where the working flow is fed down a small coiled tubing, and the ejection is lifted upward along a larger coiled tubing. The liquid flow pumped through a small coiled tubing reaches the downhole unit, where it unfolds and passes through the ejector, creating a vacuum and picking up fluids and mechanical impurities located in the well. The downhole unit has jetting nozzles for eroding sediments and creating a solid suspension for its subsequent sucking in the ejector, for which part of the liquid being pumped (about 20%) is used. In this case, it is possible to adjust the amount of liquid discharged into the well by selecting water jet nozzles. This allows, if necessary, to increase the energy of impact on solid deposits when installing nozzles of larger diameter, or when installing smaller nozzles, create a depression on the formation. Hydraulic jet nozzles can also be completely closed, which eliminates the discharge of working fluid into the well and allows to enter the pumping mode of the borehole fluid. In the standard operating mode, the system is designed in such a way that the amount of fluid discharged into the well through the jetting nozzles corresponds to the amount picked up by the ejector, thus eliminating the absorption of working fluid by the formation and providing efficient cleanout of the well.

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