Medios auxiliares
5.5 Protección anticaídas
The main consideration in BHA selection is to ensure that a specific pay zone is penetrated or drilled as per the plan. The restriction of total hole angle may solve some problems, but it is not a cure all. Even a typical 5° limit does not assure the well is free of troublesome doglegs.
Mr. Lubinski pointed out that the rate of change in hole angle should be the main concern and not necessarily the maximum hole angle while selecting a particular BHA.
The main objective should be to drill a useful hole with a full gauge, smooth bore and free of dog- legs and key seats, offsets, spirals and ledges.
Possible solutions to control deviations are; • Packed hole theory
• Pendulum theory
7.1 PACKED HOLE THEORY
In vertical drilling, packed hole assembly is used to overcome hole crookedness and to enhance ROP. Pendulum assembly is used only as corrective measure to reduce angle when maximum per- missible deviation has been reached.
7.1.1 Packed Hole Design Factor
1. In vertical hole drilling, never use near bit stabilizer alone for drilling as it invariably causes angle build up.
2. Three or more stabilizing points are needed to form a packed hole assembly. Two points contact can follow a curved line. Addition of one more contact point will not follow a curved path and will maintain a straight path.
3. Stiffness of drill collars is another factor which play an important role in straight hole drilling. Stiffness is proportional to moment of inertia. If diameter of drill collar is doubled stiffness increases 16 times. Maximum permissible drill collar diameter in a given hole should preferably be used.
4. In hard formation, short blade length stabilizer and in soft formation, long blade length stabilizer is preferable.
7.1.2 Packed Hole Assembly Design
Following are considered pertinent parameters for designing a packed hole BHA. 1. Crooked hole drilling tendencies
(a) Mild crooked (b) Medium crooked (c) Severe crooked 2. Formation firmness
(a) Hard to medium hard formations (b) Medium hard to soft formations
7.1.3 STABILIZING TOOLS
The three basic types of stabilizing tools include the rotating blade, non-rotating rubber sleeve and the rolling cutter reamer.
1. Rotating Blade Stabilizer
Use: It is most effective in soft to medium hard formations
Types of rotating blade stabilizers: i. Integral blade type (SR)
ii. Welded blade construction (SR) iii. Shrunk-on sleeve construction (SR) iv. Replaceable metal sleeve type (RR) v. Replaceable wear pad type (RWP) (RR)
• SR = Shop repairable • RR = Rig repairable
2. Non rotating rubber sleeve stabilizers (NRRS)
Use: It is most effective in very hard formations such as lime and dolomite. The rubber sleeve is
stationary and it acts like a drill bushing. It does not dig and damage the wall of the hole. It has got few limitations like:
Limitation:
• Bottom hole temperature < 250° F • It has got no reaming ability • Sleeve life is short in rough walls
3. Roller cutter reamers
Use: These are used for reaming and added stabilization in hard formation.
If any under gauge problems are encountered, roller cutter reamer should be used near the bit to overcome under gauging of the hole.
3-point reamer ( medium to hard formations) Rolling cutter reamer
6-point reamer (hard to extreme hard formations) Long(soft formation)
Short (medium to hard formation) Straight blade
Spiral blade Rotating blade stabilizer
Short (medium to hard formation)
7.2 BOTTOM HOLE ASSEMBLIES
1. MILD CROOKED HOLE TENDENCIES (for medium hard to soft formations)
The short drill collar size located between zone-1 and zone-2 is determined by hole size. Short drill collar length in ft = hole size in inches + / - 2 ft
Zone - 1: Some type of long blade stabilizer directly above the bit Zone - 2: Blade stabilizer 30 feet above zone-1
Vibration dampener/Shock sub to be used at zone-2 above stabilizer in rough drilling
conditions.
Blade stabilizer 30 feet above zone-2 (in a medium size hole, like 8-1/2”) Zone- 3:
Blade stabilizer 60 feet above zone-2 (in a larger size hole, 12-1/4” or larger)
2. MILD CROOKED HOLE TENDENCIES (for hard formations) Zone-1: Three point reamer directly above the bit
Zone-2: Three point string reamer 30 feet above zone-
Vibration dampener/shock sub to be used at zone-2 above stabilizer in rough drilling conditions. Zone- 3 : Three point string reamer or a non-rotating rubber sleeve stabilizer (NRRS) 30 ft above
zone-2
Note : Any stabilizers run above zone-3 would be used only to prevent the drill collars from
buckling or becoming wall stuck and in most cases would have little effect on directing the bit.
ZONE - 3 ZONE - 3 ZONE - 3
Vibration dampener Vibration dampener Vibration dampener
ZONE - 2 ZONE - 2 ZONE - 2
ZONE - 1 ZONE - 1 ZONE - 1
3. MEDIUM CROOKED HOLE TENDENCIES (for soft to medium hard formations)
One or two long blade stabilizers directly above the bit (for soft formation)
Zone-1
Combination of a reamer and a blade stabilizer (for medium hard formation) a) For medium size and larger holes a 10-15 foot long, large diameter drill collar
are required to be used between zone-1 and zone-2.
b) for smaller holes less than 7” in diameter would require shorter drill collar not more than 6-8 ft long. The reason for this is to enhance stiffness.
Two long blade stabilizers (for soft formation)
Zone- 2
Combination of a reamer and a blade stabilizer (for medium hard formation)
Vibration dampener/shock sub to be used at zone-2 above stabilizer in rough drilling
conditions.
a) For medium size (8-1/2”) and larger holes, a 30 ft long, large diameter drill collar would be used between zone-2 and zone-3.
b) For smaller hole size 10-15 ft long, large diameter drill collar are required to be used between zone-2 and zone-3
One Long blade stabilizer (for soft formation)
Zone- 3
String reamer or NRRS or blade stabilizer (for medium hard formation) A large diameter 30 ft long drill collar is required to be run between zone-3 and zone-4
Zone- 4 : The tools used in zone-4 can be the same type as tools used in zone-3 4. MEDIUM CROOKED HOLE TENDENCIES (for hard formations)
Zone-1 : A 6-point reamer just above the bit Zone-2 : One string reamer
Vibration dampener/shock sub to be used at zone-2 above string reamer in rough drilling
conditions.
Zone-3 : One string reamer or one NRRS stabilizer
5. SEVERE CROOKED HOLE TENDENCIES(for medium hard to soft formations)
Three blade stabilizers directly above the bit (for soft formation)
Zone-1
Combination of a reamer and blade stabilizer (for medium hard formation) a) For medium size and larger holes a 10-15 foot long, large diameter drill collar are required to
be used between zone-1 and zone-2.
b) For smaller holes less than 7” in diameter would require shorter drill collar not more than 6-8 ft long. The reason for this is to enhance stiffness.
Two long blade stabilizers (for soft formation)
Zone- 2
Vibration dampener/shock sub to be used at zone-2 above stabilizer in rough drilling conditions.
a) For medium size (8-1/2”) and larger holes, a 10-15 ft long, large diameter drill collar would be used between zone-2 and zone-3.
b) For smaller holes less than 7” in diameter would require shorter drill collar not more than 6-8ft long. The reason for this is to enhance stiffness.
One Long blade stabilizer (for soft formation)
Zone- 3
String reamer or NRRS or blade stabilizer (for medium hard formation) A large diameter 30 ft long drill collar is required to be run between zone-3 and zone-4
Zone- 4 : The tools used in zone-4 can be the same type as tools used in zone-3 7.3 BHA FOR DEVIATED HOLE
1. MOTOR KICK-OFF AND BUILD UP ASSEMBLY
1. Bit
2. Motor (preferably high speed ,low torque) 3. Float valve (shallow kick-off point only)\ 4. Bent sub
5. Orientation sub
6. Non-magnetic drill collar (monel) 7. Limited drill collar (1-2 stands) 8. 1 HW drill pipe stand
9. Drilling jar (over 500 m) 10. HW drill pipes (15 to 30 nos) 11. Drill pipes
2. ROTARY BUILD UP
This assembly is run generally to finish build up initiated with motor and bent sub. The purpose of this standard build up assembly:
i) To complete the build up before the straight hole section ii) To ream the hole prior to run stiff “hold” assembly. The build up assembly consists of:
1. Bit
2. Near bit stabilizer (spiral blades not too long) 3. One drill collar non-magnetic
4. D/C as required
5. One or two HW drill pipe stands. 6. One drilling jar
7. HW drill pipes 8. Drill pipes
3. HOLDING BHA
1. Bit
2. Stabilizer near bit (full gauge) 3. 9 m Monel
4. Stabilizer (full gauge) 5. Required drill collars 6. 1-2 HW drill pipe stands 7. Drilling jar
8. HW drill pipe stands 9. Drill pipes