Developing and Field Implementation of a State-of-the-Art BHA Program
- David C-K. Chen (Halliburton Co.)
- Document ID
- Society of Petroleum Engineers
- Latin American & Caribbean Petroleum Engineering Conference, 15-18 April, Buenos Aires, Argentina
- Publication Date
- Document Type
- Conference Paper
- 2007. Society of Petroleum Engineers
- 1.6 Drilling Operations, 1.5 Drill Bits, 1.6.6 Directional Drilling, 1.6.2 Technical Limit Drilling, 1.6.1 Drilling Operation Management, 1.12.1 Measurement While Drilling, 1.4.1 BHA Design, 1.10.1 Drill string components and drilling tools (tubulars, jars, subs, stabilisers, reamers, etc), 1.4.4 Drill string dynamics
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This paper presents the development and field implementation of a state-of-the-art bottomhole assembly (BHA) program using the industry's first generic algorithm based on Lubinski's equations. The strengths of the new BHA program are accuracy and computation efficiency, as compared to the conventional finite-element based BHA programs. In addition, the new program integrates static and dynamic models so that users can run both models in the same application. Using the new algorithm, the static model is designed mainly for directional drilling applications, such as optimal BHA design for maximum steerability, bending moment calculations to minimize fatigue failure, and BHA sag corrections to improve survey quality. The dynamic model is based on a hybrid of analytical and finite-element methods to calculate the critical rotary speeds of the BHA. This paper describes the significance of applying these features in a user-friendly application to maximize drilling performance.
Bottomhole assembly (BHA) modeling is always an essential part in directional drilling. A state-of-the-art BHA program enables many critical features, such as (i) designing a BHA to optimize directional performance, (ii) optimizing stabilizer locations to minimize vibration and increase downhole tool reliability, and (iii) improving survey data by correcting the BHA sag. Since the 1950s, several different methods have been developed and applied in the drilling industry to build the BHA models. 1-7
In general, the challenges encountered in developing a computationally efficient, flexible, and accurate BHA model can be summarized as follows:
- Nonlinear differential equations
- Unknown upper boundary conditions at the tangential point (location and orientation)
- Unknown boundary conditions at stabilizers
- Collars and wellbore wall contacts
- Large deformation caused by bent housing motor or the bend in rotary steerable tools
The most commonly used method in BHA modeling is probably the finite-element method because it is easy to develop and use. However, to the knowledge of the author, many commercial finite-element based BHA programs are still based on the small deformation theory. As a result, they have been shown to lack the accuracy required to model steerable assemblies, such as motor or rotary steerable systems. Finite-element modeling is also cumbersome in handling the collars and wellbore contact. To accurately model steerable systems, the semi-analytical methods are usually required, but semi-analytical methods are inflexible and difficult to program. They are often designed to analyze some specific BHA models and are limited to BHAs with rather simple configurations.
The objectives of developing a state-of-the-art BHA program include the following:
- Accuracy. It should provide the most accurate modeling results possible, especially for the motors and rotary steerable systems in which conventional finite-element based programs fail.
- Flexibility. The new BHA program should be capable of modeling any BHA configuration without restriction, as well as of handling the collar and wellbore contacts. The program should also allow users to model special drilling tools, if needed.
- Computational efficiency. The program will primarily be used on laptop computers by engineers. The computational time should be less than a few seconds for the most complex BHA model.
- Integrated static and dynamic analyses. The program should be capable of running static and dynamic models in the same application.
- User-friendly interface. Because the program will likely be used in the office as well as at rig sites, the program must be easy to run with an intuitive user interface.
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