Direct Flow From Pump Xxsfuced Flow From Wm

E — Valve reversing. Hammer dropping and valve about to drop. A conventional tungsten carbine tri-cone bit is attached to the anvil in full-scale laboratory and field tests.

F — Hammer striking anvii.

Hammer is driven down by gravity, hammer spring 14 and pressure drop of fluid through small passage above chamber 16. Fluid passes through chamber 18 into bit.

D — Hammer reversing. Pressure above valve lip is relieved through communication of port 29 with low pressure chamber 28. Area 31 is now at higher pressure than area 24 and valve accelerates, hammer drops.

E — Valve reversing. Hammer dropping and valve about to drop. A conventional tungsten carbine tri-cone bit is attached to the anvil in full-scale laboratory and field tests.

F — Hammer striking anvii.

Hammer is driven down by gravity, hammer spring 14 and pressure drop of fluid through small passage above chamber 16. Fluid passes through chamber 18 into bit.

combined with bit rotation. Such a technique has the basic features of both rotary and cable tool drilling.

A recent development employing this drilling mechanism is the hammer drill designed and tested by the Gulf Oil Corporation.50'51 The bit is rotated under applied "weight, percussive blows being furnished by a mud engine powered by the drilling fluid. The percussion frequency is on the order of 600 strokes/min. The mechanical operation of the engine is shown in th& series of Figure 8.28. Considerable laboratory and field test data indicate that large increases in penetration rate may be obtained. Comparative laboratory results from drilling in granite are shown in Figure 8.29.

Although still in the experimental and development stage, this device holds considerable promise. Advantages of increased drilling rate, longer bit wear (attributed to lower rpm and lighter bit weights), and less hole deviation have been claimed by the tool's developers. Field trials have indicated that the mud engine can operate for 60 to 100 hours without maintenance. At this time it appears that the mud-powered hammer drill shows considerable promise for hard rock drilling. Further field tests are required for industry's acceptance.

The Battelle Memorial Institute scientists have also experimented with a high frequency percussive drilling device in which vibrations (several hundred reversals per second) are imparted to the bit by an electro-

10,000

40,000

20,000 30,000 Weight on bit, lb

Fig. 8.29. Comparative penetration rates of conventional vs. the hammer drill. Laboratory data — atmospheric pressure. Courtesy Petroleum Engineer.50

10,000

40,000

20,000 30,000 Weight on bit, lb

Fig. 8.29. Comparative penetration rates of conventional vs. the hammer drill. Laboratory data — atmospheric pressure. Courtesy Petroleum Engineer.50

magnetic mechanism. This is powered by alternating current transmitted down specially designed cables, which fit inside the drill pipe and remain stationary while the pipe turns.2

Very little data on the penetration rates obtained with this vibratory drill are available. Equipment failures and other operating troubles have prevented its thorough testing. This particular drill must be classed as highly experimental until further data are available.

8.73 The Pellet Impact Drill

An extremely interesting and radical departure from conventional drilling methods is the pellet impact drilling technique developed by the Drilling Methods Section of the Carter Oil Company Research Laboratory in Tulsa, Oklahoma.62 This method of drilling utilizes the high velocity, random impact of steel pellets to cause rock failure. The process may be visualized from Figure 8.30. The high velocity jet stream from the primary nozzle draws drilling fluid and pellets into the secondary nozzle and discharges them against the rock. The pellets are then lifted off bottom by the drilling mud; they then re-enter the aspirator section, and are recycled. Additional pellets are suspended as a cloud above the primary nozzle due to the high ascending velocity alongside the enlarged secondary nozzle section.

Pellet cloud

Pellet cloud

Drill string

Primary nozzle

Bridging structure

Secondary nozzle

Circulating pellets

Fig. 8.30. Schematic operation of pellet impact drill. After Eckel,52 courtesy AIME.

Drill string

Primary nozzle

Bridging structure

Secondary nozzle

Circulating pellets

Fig. 8.30. Schematic operation of pellet impact drill. After Eckel,52 courtesy AIME.

The apparent advantages of this method are elimination of drill pipe rotation and the attendant benefits; in particular, there is no necessity for frequent drill pipe removal, since the pellet supply can be replenished from the surface. This latter factor could result in the elimination of heavy hoisting equipment.

The experimental difficulties encountered and the necessary modifications made by the Carter engineers and scientists required an estimated 37 man-years of research prior to publication of the results cited here. Some of these problems were:

  • 1) Determination of the optimum off bottom spacing for the secondary nozzle. This was found to be from 2.8 to 3.4 nozzle diameters.
  • 2) Nozzle diameters
  • a) The primary nozzle had to be large enough to permit the desired flow rate at the available pressure drop.
  • b) The secondary nozzle had to be large enough to prevent jamming of the pellets: the ratio of pellet diameter to nozzle diameter had to be less than 0.5. The drilling rate as related to nozzle area ratio and input fluid horsepower is shown in Figure 8.31.
  • 3) Drilling fluid: water was superior to all those tested, including air.
  • 4) Pellet charge or total quantity of pellets in the system. The drilling rate was insensitive to this, from saturation charge (maximum drilling rate) to 2\ times the saturation charge.

These are only a few of the problems encountered, but they serve to illustrate the complexity of the experiments.

Some drilling results are shown in Table 8.2. Certainly these penetration rates are lower than those obtainable by conventional methods. The pellet impact drill is not considered economic at the present time; however, it is of extreme fundamental importance, as it demonstrates a completely new concept of oil well drilling. As stated by the authors of the reference cited, the purpose of the paper was to make the findings of this work a matter of record, in the hope that the general knowledge of the process might be a guide for other developments.

TABLE 8.2

Results op 9 in. Pellet Impact Drilling Tests

TABLE 8.2

Results op 9 in. Pellet Impact Drilling Tests

Hole

Avg. depth

Average

diameter, in.

drilled

drilling

Rock

Min. Max.

per test, ft

rate, ft/hr

Okla. marble

9f 111

2

7.5

(soft rock)

Virginia limestone

9Í 10

1.5

4

(medium rock)

Pink quartzite

91 9i

1.25

0.5

  • hard rock) 8.74 Use of Retractable Bits
  • hard rock) 8.74 Use of Retractable Bits

Since trips consume a large amount of rig time, considerable thought has been given to designing retractable bits which can be changed without withdrawing the drill string. Field tests of this process have indicated economic feasibility, and this technique should receive increased attention in future years.63 Casing of the proper size is used as drill pipe and is never removed from the hole. Worn bits are replaced

Test Conditions 5B-ga. pellet 67 gpm

  1. nozzle = 1.28" i.d. by
  2. 75" long V8" dia. steel pellets (6V2 lb) 5 off bottom cycle 4" dia hole

-

\

y

S

BM

rilling Iford

rate ¡mes

n tone

S

\

H

Horse

powei

i

h

Was this article helpful?

0 0

Post a comment