Drilling Hydraulics-A Study of Chip Removal Force Under a Full-Size jet Bit

Abstract

Bit hydraulics play an important role in the drilling process. The beneficial action of the fluid's impacting, cleaning the bottom of the hole and the bit teeth, and carrying particles into the annulus is well established. What is not well known or commonly agreed upon is bow this beneficial action can be made most effective. To understand better the drilling hydraulics phenomenon, laboratory tests were carried out with phenomenon, laboratory tests were carried out with full-scale bits and a simulated hole bottom. An earlier paper described the pressure distribution on the hole bottom as it varied with nozzle size, number, and extension. This paper discusses the way the force acting on a stationary chip varies with these same parameters and also includes The effect of chip size and fluid density and viscosity. The results show that closing one or two nozzles or extending the nozzles increases chip removal force and should assist is cleaning the hole and, in some cases, increase penetration rate. Fluid velocity, nozzle diameter, and chip size are the most important factors affecting chip removal force. Fluid viscosity plays a minor role. These findings reinforce and broaden the conclusions reached in the pressure distribution studies. It was also found that chip removal force correlates more closely with jet impact and horse power than with velocity or nozzle Reynolds number. Introduction Bit hydraulics are difficult to study. If tests are carried out in the field, there are uncertainties regarding down-hole conditions and whether these conditions change during a test. If the tests are carried out in the laboratory, results are usually more clear-cut, but then there is the question of how well the tests simulate field conditions. The most reliable insight into the over-all hydraulics problem is probably reached by blending the results problem is probably reached by blending the results of all types of work; no single study fits together more than a few pieces of the intricate puzzle. Past work in drilling hydraulics has been in the following categories: field testing, similar to that of Thompson, Spear, and Eckel; drilling tests in the laboratory, similar to those of Horner el al, van Lingen, Feenstra and van Leeuwen, and Eckel; and laboratory nondrilling tests like those of McLean and Cheatham and Yarbrough. other significant work includes the Kendall and Goins theoretical paper on optimization and that portion of Bingham's series on "a new approach portion of Bingham's series on "a new approach to interpreting rock drillability" that deals with bit hydraulics. The work reported here fits in the category of laboratory nondrilling. It is aimed at explaining how nozzle size, jet velocity, fluid properties, etc., affect tat takes place as the fluid leaves the nozzle impinges on the hole bottom, and begins to return to the surface. This work differs from Refs. 4 through 7 in that no actual drilling took place. In a sense, this detracts from its usefulness; on the other hand, we feel that we were able to maintain closer control over test conditions because we did not have the problems of rock variability, drilling fluid problems of rock variability, drilling fluid contamination, and the other phenomena involved in drilling tests. The work in Refs. 8 and 9 described the measurement of velocities and pressures under a jet bit. Maximum jet velocity was 171 ft/sec. The work reported in this paper describes the forces caused by fluid velocities and pressures as they act on a chip. Maximum jet velocity was 286 ft/sec. An earlier paper, described the pressure distribution on the bottom of the hole as it is affected by nozzle size, number, and extension. Conclusions included the desirability of plugging one or two nozzles, using extended nozzles and a correlation of pressure distribution with jet velocity, nozzle diameter, and the distance between the nozzle and hole bottom. The present work is a continuation of the same study and was set up to find out what happens when fluid moving across the hole bottom meets an object in its path. In a sense, it a basic attempt to study hole cleaning under closely controlled conditions. SPEJ P. 233

Characterization of a Pulsating Drill Bit Blaster

“…This improvement in cleaning efficiency as a function of the product of jet velocity and flowrate was independently confirmed in later research with the note that the primary deterrent to achieving maximum drilling rates was the inability of the drilling system to remove rock cuttings efficiently enough to prevent interference with the drilling action (Mclean & Cheatham, 1964) (Yarbrough, 1964. Building on this knowledge, a full size jet-bit was tested in an attempt to further understand both bit cleaning and a phenomenon known as "chip hold down" in which the cutting chips generated are held to the well bottom by the pressure of the drilling fluid column (Sutko, 1973). By closing one or two bit nozzles the chip removal force was increased and it was stated that this should assist in the cleaning of the bore and improve the ROP (Sutko, 1973).…”

“…Building on this knowledge, a full size jet-bit was tested in an attempt to further understand both bit cleaning and a phenomenon known as "chip hold down" in which the cutting chips generated are held to the well bottom by the pressure of the drilling fluid column (Sutko, 1973). By closing one or two bit nozzles the chip removal force was increased and it was stated that this should assist in the cleaning of the bore and improve the ROP (Sutko, 1973). Furthermore, the removal force acting on a chip is predominantly due to inertia and friction caused by fluid viscosity plays a minor role (Sutko, 1973).…”

“…By closing one or two bit nozzles the chip removal force was increased and it was stated that this should assist in the cleaning of the bore and improve the ROP (Sutko, 1973). Furthermore, the removal force acting on a chip is predominantly due to inertia and friction caused by fluid viscosity plays a minor role (Sutko, 1973). In theory, a pulsating bit like the DBB could overcome the initial inertia required to move a chip more effectively than a constant pressure jet drill bit since the initial pressure wave created when a fluid path is opened in the DBB has greater force than a bit with the nozzles constantly open due to the back pressure developed when the fluid paths are closed.…”

Engineering Opportunities and Challenges in Drilling

“…Galle and Woods' 3 calculations to select the best bit weight and rotary speed for minimum cost drilling and Kendall and Goins' 4 techniques to select bit jet sizes and pump speeds for maximizing hydraulics are two of the better-known engineering optimization papers. Many other papers [5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20][21][22] have refined and broadened these basic techniques, and have developed criteria for optimizing bit selection, mud properties, and other drilling parameters.…”