BHA.pptx

BHA

1. MODULE-8 Bottom Hole Assembly Deviation without Deviating Tools By GAURAV HAZARIKA Assistant Professor School of Petroleum Technology Pandit Deendayal Petroleum University DRILLING ENGINEERING II

2. BOTTOM HOLE ASSEMBLY The lower portion of the drill string, consisting of the bit, bit sub, a mud motor (in certain cases), stabilizers, drill collar, heavy-weight drill pipe, jarring devices ("jars"), and crossovers for various thread forms. It must provide force for the bit to break the rock (weight on bit), survive a hostile mechanical environment, and provide the driller with directional control of the well.

3. BOTTOM HOLE ASSEMBLY Often the assembly includes a mud motor, directional drilling and measuring equipment, measurements-while-drilling tools, logging-while-drilling tools and other specialized devices. In general, there are three types of BHA Slick Pendulum Packed BHA

4. Slick BHA A slick BHA may be defined as one in which no stabilizer is used. The drill string simply consists of bit, drill collars and drill pipe. Thus, this type of BHA is suitable only for mild crooked hole formations. Slick BHAs are seldom used except to drill to kick-off point in directional wells.

5. Pendulum BHA BHA using the pendulum technique are primarily used to reduce hole deviation, as exemplified by the drop-off section of an S-type directional well.

6. Pendulum BHA Used to drill soft, unconsolidated formations Technique relies on the principle that the force of gravity may be used to deflect the hole back to vertical. The force of gravity F (shown below) is related to the length of drill collars between the drill bit and the point of tangency called 'active length' of drill collars. Increasing the active length means that the vertical force is increased and the hole is quickly deflected back towards the vertical.

7. Pendulum BHA The actual force which brings about the deflection towards vertical is FSinI which acts perpendicular to the well-bore axis. FCosI maintains the present hole direction & WOB. Thus Increment of FSinI to increase deviation

8. Pendulum BHA Maximum pendulum force can be obtained by placing the first string stabilizer as high as possible above the bit so that the active length of the drill collars will not touch the walls of the hole. However, if the distance from the bit to the first stabilizer is made too large, there is a danger that the 'active length' of the drill collars will contact the low side of the hole, thus reducing the pendulum effect. Wilson pointed out that a second stabilizer 30 ft. above the first string stabilizer should be used to reduce the lateral force on the first stabilizer.

9. Pendulum BHA

10. Fulcrum BHA BHA using the fulcrum (Simple Machine) technique are primarily used to increase hole deviation, as exemplified by the build-up section of a directional well. The Near Bit stabilizer behaves like a fulcrum point for this effect

11. Vaarious BHA

12. Packed Hole Assembly The packed hole assembly relies on the principle that two points will contact and follow a sharp curve, while three points will follow a straight line.

13. Mild crooked hole packed BHA The three-point stabilization is provided at Zone 1: immediately above the bit Zone 2: immediately above a Pony Collar Zone 3: on top of a standard drill collar Vibration dampener (if required) should be placed at Zone 2 for maximum effectiveness A vibration dampener is used to absorb bit bounce and prevent vibrations from being transmitted to the surface.

14. Medium crooked hole packed BHA A second stabilizer is included at Zone 1 in order to provide increased bit stabilization against the deviation effects of the formation. Zones 2 and 3 are similar to those of Type (1) packed BHA.