Brocas

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Prepare a graph that shows the break-even costs of $50/ft as a function of penetration rate and bit life. Label the región of the graph tha shows combinations of penetration rate and bit life which are not aceptable. If the initial penetration rate of the new bit during the first hour is 4 ft/hr, what would you recomend?

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5.10. Grade the bit shown in the photograph below.

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El grado de una broca depende de tres factores que son:

- Steel teeth: medida de la altura del diente perdido o desgastado.

- Bearings: medida del rodamiento que se ha desgastado

- Gauge wear: medida del desgaste en el diámetro.

Respuesta: Grado T-8, B-8, G-O

5.11. Describe the difference between self-sharpening and abrasive tooth wear. Discuss what is done by the bit manufacturers to promote self-sharpening bit wear on milled-tooth, rolling-cutter bits.

Normalmente el carburo de tungsteno en cual se localiza en la parte posterior de la capa de diamantes tiende a desgastarse mucho más rápido que el diamante poli cristalino, esto se debe a que presenta una baja resistencia a la abrasión y por tal motivo los cortadores PDC siempre conservan un borde afilado mientras se produce la acción de desgaste del mismo.

Mientras más se utiliza una barrena de diamantes estos se van desgastando de tal modo que se comienzan a tornar lizos, esto también produce una reducción considerable en su eficacia al momento de cortar la roca lo cual sucede también con los dientes en una barrena de conos y comienzan a perforar a una menor velocidad de la habitual. A diferencia de las barrenas de cono esto no sucede con las PDC ya que estas conservan una velocidad más alta de perforación a lo largo del intervalo perforado

5.12. A 9.875 in. Class 1-1-1 bit drilling from a depth of12000 to 12200 ft. In 12 hours. The average but weight and rotary speed used for the bit run was 40000 lbf, 90 rpm respectively. When a bit was pulled, it was graded T-6, B-6. The drilling fluid was a barite- weight clay/ water mud having a density of 12 lbm/gal.

- Compute the average formation abrasiveness constant for this depth interval.

Using the table 5.8 we obtain:

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Using the eq. 5.11:

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Using eq. 5.13:

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- Estimate the time required to completely dull the bit teeth using a bit weight of 45000 lbf and the rotary speed of 100 rpm.

W=45000lbf

N= 100 rpm

Using eq. 5.11:

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- Compute the bearing constant for this depth interval.

Using table 5.9 we obtain:

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- Estimate the time required to completely dull the bearing using a bit weight of 45000lbf and the rotary speed of 100 rpm

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5.13. Compute the bearing constant, TB , for the bit of Example 5.3 if the drilling fluid were a weighted clay-water mud (barite mud). Use values of B1 and B2 recommended in table 5.9.

DATOS:

De la tabla 5.9

B1 = 1.0

B2= 1.5

Del Example 5.3:

W = 45000 lbf

N = 90 RPM

db = 8.5 in

tb = 10.5 hours

bf = 6/8 = 0.75

SOLUCIÓN:

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5.14. Field data observed on 7,875 in., Series 6, roller-bearing bits at a rotary speed of 60rpm shows an average bearing life of 32 hours for a bit weight of 5 700 lbf/in. and 45 hours at 3800 lbf/in. Compute the apparent bearing weight exponent, B2, and bearing constant, , for this bit type.[pic 46]

DATOS:

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SOLUCIÓN:

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