Expanding the Use of Turbodrills in Coiled Tubing and Workover Applications

Abstract

With the ever increasing demands placed on downhole tools with well reaching deeper depths, increasing bottomhole temperatures, and reduced bottomhole pressures these hostile environments place increasing demands on the tool providers to supply tools that will withstand these ever increasing demands. One way to overcome these demands is to utilize a purely metallic drilling tool such as a downhole Turbodrill. The turbine power section and bearing section are constructured with only metallic components eliminating the requirement for elastrometic stators, which have proven problematic, when bottomhole temperatures reach or exceed the rated temperatures or nitrogen is required to ensure well integrity. Traditionally turbodrills have been utilized for the most extreme high pressure and/or high temperature, hard rock-drilling applications - this paper will expand on some of the latest improvements to the tool design such as blade design which has enabled the tool length to be reduced allowing easier rig up for coiled tubing applications. Testing of the tools as well as case histories are included, that will illustrate that the Turbodrills can be used as successfully in challenging drilling and work-over applications. Introduction Coiled Tubing use over the last 2 decades has increased due to wider acceptance in the industry, due to improvements in the material manufacture and quality assurance management of the coil, with these improvements the applications in which coiled tubing can be utilized has expanded. In the mid to late 1980's the Thru-Tubing milling and fishing applications also expanded with the purpose designed tools that could be utilized to complete work-over applications. The design and introduction of conventional positive displacement motors, in diameters that were small enough to operate within the Thru-Tubing applications for cleanout operations, such as scale removal and cement milling, despite their evolution the small diameter PDM's proved to have limitations relating to the fluids that could be pumped through them. Special chemically resistant elastomers have been developed in an attempt to fix the reactivity of the elastomeric components of these tools to the drilling fluids. While the quantity of elastomer used in the stator lining has been reduced and wall thickness of the remaining elastomer has been evened across the profile these developments have had limited success in the 2-phases gaseous drilling fluids used in thru-tubing applications, problems still exist with explosive decompression of the stator elastomer. Further, the ever increasing well depths, increasing bottom-hole temperatures and increasing requirements to use exotic drilling fluids (in order not to harm hydrocarbon production) these elastomeric positive displacement tools have continued to be unreliable in the harsher thru-tubing environments. One of the main differences between the conventional PDM and the Turbodrill is the fact the Turbodrill is all metallic tool, (Fig 1.) eliminating the problems associated with the stator elastomer reactivity to gas as well as exotic drilling fluids.

Design and Output Performance Model of Turbodrill Blade Used in a Slim Borehole

“…Reference [19] examined the history of turbodrilling and described a number of the harshest and most complex drilling environments in which turbodrills have been notably successful. Reference [20] described several improvements to the turbodrill design (such as blade design) that have enabled reductions in the tool length, thereby allowing easier rig up for coiled tubing applications. Mokaramian et al [21] conducted computational fluid dynamics (CFD) simulations to determine the performance of a single-stage turbodrill with different rotation speeds and mass flow rates.…”

Design and Development of Turbodrill Blade Used in Crystallized Section

“…Another research [ 12 ] introduces a more efficient 2-7/8 in-diameter turbodrill and a novel 4-1/8 in-diameter drill bit for drilling with coiled tubing. Some of the coiled turbine blades [ 13 , 14 ] are designed on the basis of the requirements of the small diameter drilling. Jianhong et al [ 15 ] calculated the pressure drawdown at the inlet/outlet and the pressure distributions in single-stage turbine for noncoring drilling.…”