Understand the Effect of Mud Pulse on Drilling Dynamics Using Big Data and Numerical Modeling

Abstract

It is common to have measured depth exceeding 20,000 ft for unconventional oil and gas wells. To ensure the pressure pulse can be detected on the surface, many MWD tools have been designed to generate mud pressure pulse with very large amplitude. While the large pressure pulse solved the problem of sending the measured information up to the surface, it creates significant impact on drilling system energy variation and downhole drilling dynamics. This paper focuses on understanding the effects using big data and drilling system modeling. When a commonly used MWD tool generates mud pulse sequence, it chokes the flow path at designed patterns. This creates mud flow variation in the mud motor below the MWD tool. It also generates axial force variations due to pressure changes, which affect WOB. These changes cause the motor and the bit to experience significant rpm variations. The combined rpm variation and WOB variation often excite more severe axial and lateral shock and vibration. These effects are quantified by thousands of high-frequency downhole datasets and advanced numerical modeling. In the high-frequency downhole datasets, some of them are obtained from BHAs with MWD tools generating large mud pressure pulse, and some of them are obtained from BHAs with MWD tools generating smaller mud pressure pulse or transmitting the measurements using electromagnetic signal. Statistics of rpm variation and axial and lateral shock and vibrations are compared. It clearly shows that the BHAs utilizing large mud pressure pulse experience more severe torsional, axial, and lateral vibrations. When looking into specific datasets, it showed that mud pressure pulse could cause the motor to lose more than half of its rpm during the flow choking phase. Typical datasets indicate that mud pressure pulse correlates to severe high-frequency torsional oscillation (HFTO) in motorized rotary steerable BHA. An advanced transient drilling dynamics model was built to simulate the whole drilling system subjecting to mud pressure pulse incurred loading conditions. It was found that large-magnitude mud pressure pulse induced more stick/slip and axial and lateral vibrations as recorded in downhole high-frequency data. The increased rotational, axial, and lateral vibrations correspond to more loading variations in the mud motor components and PDC cutters on the drill bit. These variations could cause accelerated damage to the drill bit and downhole tools. In summary, large mud pressure pulse utilized by some MWD tools introduces significant rpm variation and shock and vibration, which is quantified by big data and further demonstrated by drilling system modeling. The information could help make decisions on BHA design and tool selection to achieve improved drilling performance and reduce the risk of premature tool failure.