Design and experimental study of a new hydraulic tool for LCM plugging while drilling

Abstract

Big Data Analysis from the worldwide field shows that lost circulation is a common phenomenon in drilling and the success ratio of remedial treatment for lost circulation is low. It is not only because of these complexities of the formation, but also because of the poor performances of the plugging materials and technologies. This paper proposes a new method in plugging, which is based on a particular physical method for lost circulation controlling and plugging while drilling. This method is different from these traditional treatments, which only use chemical methods. Through a hydraulic tool manufactured for using in drilling process, the drilling fluid will have a diffluence at a constant rate from the jet of the hydraulic tool which is installed on the drilling pipe and the fluid laden with particles can be injected into the natural or induced fractures of the borehole wall which may lead to lost circulation. Combined with the corresponding drilling fluids which have been tested in the laboratory, the additives such as ground marble, ground nutshells, fibers and graphite in the drilling fluid are quickly pushed into the fractures because of the differential pressure provide by the hydraulic tool, then form a firm seal at the mouth of the fractures which could isolate fluid pressure in the wellbore and prevent effective pressure communication to interfere the extension of the fracture. What’s more, according to the stress cage theory, when these sealing particles which prop the fracture open, act as wedges to compress the rock around the wellbore, the hoop stress could be increased, so that the WPC (wellbore pressure containment) could be improved. In this paper, a lab test and a field experiment are presented. The experiment result reveals that the hydraulic tool is able to force more material into the fracture, bridge at the mouth of the fracture, form a stable plug in the fracture to isolate the hydraulic pressure in the wellbore, and add a nearly impermeable mud-cake on the wellbore wall to change the effective stress concentration around the borehole. The result demonstrates that the hydraulic tool can provide an effective preventive treatment for lost circulation and an improvement of WPC. It is then feasible to avoid lost circulation events when using this hydraulic tool.