The drilling bottom hole assembly (BHA) is one of the components of the Drilling String, which is below the Drill Pipes. The most common components of the BHA are Drill Collars, Stabilizers, Shock Absorbs, Jars, Reamers, Heavy Weight Drill Pipes, and The Drilling Bit.
The purpose of the Bottom Hole Assembly BHA is to drill a usable hole economically. This objective is achieved with the proper Drill Bits Selection and Drill Collars selection, which are required to provide high WOB bit weights to Improve ROP (The Penetration Rate).
Stabilizers are one of the bottom hole assembly BHA components needed to minimize the rate of hole angle change and prevent the formation of doglegs and key seats.
Shock absorbers play an important part in prolonging the service life of the bit and drill pipe. Downhole drilling jars may be needed to unstick the BHA.
The Bottom Hole Assembly BHA design is based upon the requirements of having enough weight transfer to the bit (WOB) to be able to drill and achieve a sufficient Penetration Rate (ROP), giving the Driller or Directional Driller directional control to drill as per the planned well trajectory and to also include whatever
Logging While Drilling (LWD) / Measurement While Drilling (MWD) tools for formation evaluation. As such Bottom Hole Assembly BHA design can vary greatly from simple vertical wells with little or no LWD requirements to complex directional wells which must run multi-combo LWD suites.
Before running a BHA, most oilfield service providers have software to model the BHA behavior, such as the maximum WOB achievable, the directional tendencies & capabilities, and even the natural harmonics of the assembly to avoid vibration by exciting natural frequencies.
Main Categories Of Bottom Hole Assembly BHA Used In Oilfield
Rotary Bottom Hole Assembly BHA Drilling
Rotary assemblies are commonly used where formations are predictable and rig economics are an issue. In such an assembly, the weight of the drill collars gives the BHA the tendency to sag or flex to the low side of the hole; collar stiffness length and stabilizer diameter and placement are engineered as a means of controlling the flex of the BHA. This will bring about the desired hold, build or drop tendency.
The ability to vary the directional tendency of the assembly comes from varying the weight on the bit. A fixed assembly has only one directional tendency. The weight on the bit allows you to tune that tendency
Directional Bottom Hole Assembly BHA Drilling:
You may need to use a mud motor with a bent sub or use rotary steerable systems
Bottom Hole Assembly BHA Drilling Components:
Heavy Weight Drill pipe ( The Top most BHA Component)
Heavy Weight Drill Pipe Specs are important to understand as it is the entrance of the heavyweight drill pipe design. In this article, we will discuss its specs and how to select in the drill string design. In addition to that, we will talk about its main functions. You can also download the spec sheets from any size of heavy-weight drill pipes.
Drill Collar (a predominant component of the BHA components)
Drill collars (D/C) are large diameter-small bore steel pipes that possess a great weight and great stiffness. While designing BHA, drilling engineers place D/Cs above the Drilling Bit as D/Cs are the predominant component of the BHA components. To select the proper D/C, you will have to have all information about Drill collar Weights, Size, Specs, Definition, lengths & Types.
Stabilizers :
Drilling stabilizer types & design is the main subject of this article. First, we will define a stabilizer as one of the bottom-hole assembly BHA components. Then we will move to the stabilizer application. And finally, we will talk about its types.
Reamers
Drilling reamers types are the subject of our article. We can say that reamers types are: under-reamers type, Roller Reamers Type, RFID Reamers Type, Near-Bit Reamers Type, and Expandable Reamers Type.
Shock Absorbers
Main Headings :
- What Is The Meaning Of Shock Absorbers
- Shock Absorbers Application
- What Are The Drilling Bit Oscillations
- How To Use Shock Absorber To Eliminate The Drilling Bit Oscillations
- The Limitations Of Drilling Shock Absorbers
- Positioning Of Drilling Shock Absorbers In The Drilling String Bottom Hole Assembly BHA
- Drilling Shock Absorber Mechanism
Jarring Devices
Drilling jar placement design is important while drilling. In general, jars are one of the bottom hole assembly BHA components that generate upward or downward impact loads to free stuck pipe or release a fish. Many factors affect the decision of when to use jars and where to position them for maximum benefit.
Drilling Bit
Drilling Bits article includes many articles which cover what you will need to understand Bits types, selection, and design.
Main Headings:
- TYPES OF DRILLING BITS: Rolling Cutter Bits, Fixed Cutter Bits
- BIT DULL GRADING
- DRILL OFF TEST
- FACTORS AFFECTING PENETRATION RATE
Drill Pipes ( Not Bottom Hole Assembly BHA Components)
Drill pipes are not one of the bottom hole assembly BHA components, but we shall mention it as a drill string component. This article mainly explains the drill pipe description in simple points to understand how you will select the drill pipes in the drill string.:
- Drill Pipe OD
- Drill Pipe Nominal Weight
- The Pipe Grade
- The tool joint and type of upset
- Drill Pipes Tool Joints Types / Upset Types
- The type of connection
- The classification of drill pipe is based on wear.
- API Drill Pipes Classifications
How Drilling BHA Act / BHA Behaviour
Rotary BHA Types are designed to build, drop, or hold angles. The behavior of any rotary assembly is governed by the size and placement of stabilizers within the first 120 ft from the bit.
Additional stabilizers running higher on the drill string will have a limited effect on the assembly’s performance. Rotary assemblies are not “steerable”; a rotary assembly’s azimuth behavior (right/left turn) is nearly uncontrollable.
Second, each rotary assembly has a unique build/drop BHA tendency that cannot be adjusted from the surface. Thus, a tripping pipe for the assembly change is required to correct the wellbore course.
Rotary BHA Types
The Main Rotary BHA Types are: Slick assembly, fulcrum, and Pendulum Assembly.
