Бурение грунтовых зондов, установка энергетических колодцев

NOTE: Buoyancy factor is for STEEL only

Mud densit		Gradient psi/ft	Buoyancy Factor	Mud densit		Gradient psi/ft	Buoyancy Factor
kg/m3	lb/gall	lb/ft3	kg/m3	lb/gall	lb/ft3
1000	834	62.4	433	.873	1800	15 0	112	.779	.771
1010	8.40	62.8	436	.872	1820	15.2	114	790	.768
1030	8.50	64.3	.447	.869	1850	15.4	115	.800	.765
1060	8.80	65.8	457	866	1870	15.6	117	.810	.762
1080	9.00	67.3	468	862	1890	15.8	118	.821	.759
1100	9.20	68.8	.478	860	1920	16.0	120	.831	.755
1130	9.40	70.3	488	.856	1940	16.2	121	.842	753
1150	9.60	71.8	499	853	1970	16.4	123	.852	749
1154	9.625	72.0	.500	853	1990	166	124	.862	.746
1180	9.80	73.3	509	.850	2010	16.8	126	.873	743
1200	10.0	74.8	.519	847	2040	17.0	127	.883	.740
1220	10.2	76.3	.530	844	2060	17.2	129	.894	.737
1250	10.4	77.8	540	841	2090	17.4	130	.904	.734
1270	10.6	79.3	.551	838	2110	176	132	.914	.731
1290	10.8	80,8	.561	.835	2130	17.8	133	.925	.728
1320	11.0	82.3	.571	832	2160	18.0	135	.935	.725
1340	11.2	83.8	.582	829	2180	18.2	136	.945	.722
1370	11.4	85.3	.592	826	2210	18.4	138	.956	.719
1390	11.6	86.8	603	823	2230	18.6	139	.966	.716
1410	11.8	88.3	.613	820	2250	18.8	141	.977	.713
1440	12.0	89.8	.623	817	2280	19.0	142	.987	.710
1460	12.2	91.3	634	.814	2300	19.2	144	.997	.707
1490	124	92.8	644	.810	2330	19.4	145	1.01	.704
1510	12.6	94.3	655	808	2350	19.6	147	1.02	.701
1530	12.8	95.8	.665	804	2370	19.8	148	1.03	.698
1560	13.0	97.3	.675	801	2400	20.0	150	1.04	694
1580	13.2	98.7	686	798	2420	20.2	151	1.05	.692
1610	13.4	100	.696	795	2450	20.4	153	1.06	.688
1630	13.6	102	.706	792	2470	20.6	154	1.07	.685
1650	13.8	103	.717	789	2490	20.8	156	1.08	.682
1680	14.0	105	.727	786	2520	21.0	157	1.09	.679
1700	14.2	106	738	783	2540	21.2	159	1.10	.676
1730	14.4	108	.748	.780	2570	21.4	160	1.11	.673
1750	14.6	109	.758	.777	2590	21.6	162	1.12	.670
1770	14.8	111	.769	.774	2610	21 8	163	1.13	.667

Table 15 Buoyancy Factors

Solutions to Exercises

Exercise 1 Dimensions and weight of drillpipe

a. The weight (in air) of 30 ft of 5” 19.5 lb/ft Grade G drillpipe with 4 1/2” IF connections:

21.5 lb/ft (Approx. wt.) x 30 ft = 645 lbs

b. The weight of this string in 12 ppg mud:

645 lbs x 0.817 (buoyancy factor)

= 527 lbs

Exercise 2 Drillcollar dimensions and weights

a. The weight (in air) of 200 ft of 9 1/2” x 2 13/16” drillcollar is:

220.4 lb/ft (Approx. wt.) x 200 ft = 44080 lbs

b. The weight of this string in 13 ppg mud:

44080 lbs x 0.801 (buoyancy factor)

= 35308 lbs

c.

I. D. = 4.276” I. D. = 2 13/16”

5” 19.5 lb/ft drillpipe 8 1/4” x 2 13/16” drillcollars

Exercise 3 Length of Drillcollars for a given WOB

a. The weight (in air) of 10,000 ft of 5” 19.5 lb/ft Grade G drillpipe with 4 1/2” IF connections:

21.5 lb/ft (Approx. wt.) x 10,000 ft = 215,000 lbs

b. The weight of this string in 12 ppg mud:

215,0 lbs x 0.817 (buoyancy factor)

= 175,655 lbs

c. The length of 9 1/2” x 2 13/16” drillcollars that would be required to provide

25,0 lbs WOB in 12 ppg mud:

25,0 lbs = 139 ft

220.4 lb/ft x 0.817

An additional length of drillcollars is required to ensure that the drillpipe is in tension when drilling. This additional length of collars will be required to overcome the buoyant force on the drillpipe and from the above will be equal to:

(215000 — 175655) = 219 ft

220.4 x 0.817

With an additional 15% length of drillcollar the total length of collar will be: (139 x 1.15) + 219 = 379 ft

C O N T E N T S

1. TYPES OF DRILLING BIT

1.1. Drag Bits

1.2 Roller Cone Bits

1.3 Diamond Bits

1.3.1 Natural Diamond Bits

1.3.2 PDC Bits

1.3.3 TSP Bits

2. BIT DESIGN

2.1 Roller Cone Bit Design

2.1.1. Bearing Assembly

2.1.2. Cone Design

2.1.3 Cutting Structure

2.1.4 Fluid Circulation

2.2 PDC Bit Design

2.2.1 Cutter Material

2.2.2 Bit Body Material

2.2.2 Bit Body Material

2.2.4 Profile

2.2.5 Cutter Density

2.2.6 Cutter Exposure

2.2.7 Fluid Circulation

3. BIT SELECTION

3.1 Roller Cone Bits

3.2 Fixed Cutter Bits

4. ROCK BIT EVALUATION

5. BIT PERFORMANCE

5.1 Roller Cone Bits

5.1.1 Weight on Bit

5.1.2. Rotary Speed

5.1.3. Mud Properties

5.2 PDC Bits

5.2.1 WOB/RPM

5.2.2 Mud Properties

5.2.3 Hydraulic Efficiency

LEARNING OBJECTIVES:

Having worked through this chapter the student will be able to: General:

• Describe the basic types of drillbit and the differences between a Diamond, Roller Cone and a PDC Bit

Roller Cone Bit Design:

• List the main characteristics which are considered in the design of roller cone bits.

• Describe the: various types of bearing; design features of the cones; and types of nozzles used in roller cone bits.

PDC Bit Design:

• List the main characteristics which are considered in the design of PDC bits

• Describe the: cutting material; body material; cutter rake; bit profile; cutter density; cutter exposure; and fluid circulation features in PDC and TSP bits

• Describe the differences between PDC and TSP bits.

Bit Selection:

• Describe the process of roller cone bit selection and the bit selection charts.

• Describe the fixed cutter bit selection process and the selection charts used for these bits.

Bit Evaluation:

• State the value of having an evaluation technique for drillbits.

• Describe the main causes of damage to bits.

• Describe the bit evaluation process and the IADC evaluation system.

• Grade a dull bit using the IADC dull grading system

Bit Performance:

• Describe the techniques used to evaluate the performance of a drillbit.

• Calculate the cost per foot of a bit run and describe the ways in which the cost per foot calculation can be used to evaluate the performance of a bit run.

• Select a bit on the basis of previous bit run data.

• Describe the influence of various operating parameters on the performance of a bit.

INTRODUCTION

A drilling bit is the cutting or boring tool which is made up on the end of the drillstring (Figure 1). The bit drills through the rock by scraping, chipping, gouging or grinding the rock at the bottom of the hole. Drilling fluid is circulated through passageways in the bit to remove the drilled cuttings. There are however many variations in the design of drillbits and the bit selected for a particular application will depend on the type of formation to be drilled. The drilling engineer must be aware of these design variations in order to be able to select the most appropriate bit for the formation to be drilled. The engineer must also be aware of the impact of the operating parameters on the performance of the bit. The performance of a bit is a function of several operating parameters, such as: weight on bit (WOB); rotations per minute (RPM); mud properties; and hydraulic efficiency. This chapter of the course will therefore present the different types of drillbit used in drilling operations and the way in which these bits have been designed to cope with the conditions which they will be exposed to. An understanding of the design features of these bits will be essential when selecting a drillbit for a particular operation. Since there are a massive range of individual bit designs the drillbit manufacturers have collaborated in the classification of all of the available bits into a Bit Comparison Chart. This chart will be explained in detail.

When a section of hole has been drilled and the bit is pulled from the wellbore the nature and degree of damage to the bit must be carefully recorded. A system, known as the Dull Bit Grading System, has been devised by the Association of Drilling Contractors — IADC to facilitate this grading process. This system will also be described in detail.

In addition to selecting a bit, deciding upon the most suitable operating parameters, and then describing the wear on the bit when it has drilled a section of hole, the drilling engineer must also be able to relate the performance of the bit to the performance of other bits which have drilled in similar conditions. The technique used to compare bits from different wells and operations will also be described.

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