Numerical and Experimental Investigation on the Feasibility of Horizontal Drilling With a New Type of Jet Mill Bit

Abstract

Recently, a new type of jet mill bit (JMB) has been introduced to improve the cutting transport efficiency in horizontal drilling by comminuting cuttings into dust-like particles immediately after the cuttings are generated. To promote the application of JMBs in the field, in this work, JMBs were further improved by including junk slots (JS) all around to allow cuttings to flow through the annulus and thereby prevent sticking from occurring while tripping out. Moreover, numerical and experimental investigations on the feasibility of horizontal drilling with the new type of JMB were carried out. The finite element method was used to analyze the strength of the new type of JMB, and flow field simulation analysis was also performed for JMBs with different sizes of JS. The simulation results indicated that the weakest point of the JMB was located at the bit connection instead of the bit frame, and it was demonstrated that the structural strength of the JMB met the requirements of actual working conditions. The JMB JS had a negative effect on promoting the upward return of cuttings from the bottom of the hole, and the larger the slot sizes were, the more negative the effects. Through a trip-out experiment with the new type of JMB, this paper studied the influence of the slot size on the trip-out process safety. The experimental results indicated that the minimum safe slot width was 60 mm. Finally, in a synthesis of the simulation and experimental results, the reasonable range of slot width was determined to be 60–70 mm; the aforementioned range was the most suitable for the bit based on safety and efficiency considerations. This paper provides guidance for the improvement and application of JMBs.

Flow field simulation of a hydrogeological exploration drill bit for switching coring drilling and non-coring drilling

“…Since drilling fluids flowing in a borehole follows conservation laws, including mass conservation, energy conservation, and momentum conservation, it can be regarded as a continuous, incompressible turbulent flow of a single medium [31,32]. Then, the governing equations could be derived.…”

Numerical and experimental investigation on the depressurization capacity of a new type of depressure-dominated jet mill bit

“…Please note that the junk slots or flowby of the depressure-dominated JMB is much smaller than that of the conventional bits and so is the clearance in the annulus. As Cao et al (2019) reported, the cuttings will flow out inside the bit through the cuttings-suction channel instead of the small junk slots and annulus. The other stream flows through the backward jet nozzles, mixing chamber, throat, dissociating and comminution tube, and diffuser toward the annulus between open hole and drill pipe.…”

“…Through depressuring at the bottom hole, the JMB can lower the stress on rock surface, minimize cuttings hold-down effect, and improve cuttings cleaning capacity, thus increasing the ROP (Li et al 2010;Shi et al 2018). In 2019, JMB was improved by adding junk slots around to allow cuttings to flow through the annulus instead of accumulating at the top of the JMB while tripping out and therefore avoid sticking (Cao et al 2019). This improvement reduces the risk of sticking while tripping out and increases the feasibility of field application of JMB in horizontal drilling.…”