Modelling of a Down Hole Pulsating Device

Abstract

An increased awareness of drilling costs amidst the volatile nature of the market has necessitated pushing the frontiers of drilling technology to improve efficiency thereby saving costs. It is in view of this trend that the concept of drilling using a downhole pulsating device was conceived. This method sought to optimise drilling performance by manipulating two drilling parameters; the weight on bit and transient hydraulic fluid effects in order to obtain an empirical model for subsequent simulations which Consist of includes a pilot well drilled on paper. The downhole pulsating device is fitted in the bottomhole assembly and primarily comprises of two valve plates sitting flush against each other. The bottom plate is static in the wellbore allowing fluid to pass through its centre while the top valve is rotated around the wellbore circumference by the rotor of the mud motor, thus constraining the flow in the flow path. Transient hydraulics generates pulses which impact on the drilling performance and it has been proven to enhance the rate of penetration.It was noted that there is a momentary underbalance as the downhole pulsating device undergoes through a complete opening cycle. Hence there is a need to use a rotating head to secure the well. A further advantage of this method is economically viable and it is only requires fitting the downhole pulsating device through a sub into the drill string.A model of fluid flow across a downhole pulsating device was generated using a two parameter, second degree polynomial equation, which includes the force generated and transferred to the bit, and the opening ratio of the downhole pulsating device within a unit time interval. It was also demonstrated that drilling with a downhole pulsating device exerts more hydraulic horsepower on the drill bit and provides better cleaning for the bit.

Dynamic Analysis of Bottom Hole Assembly With External Vibrating Force Excitation

“…As a result, it was proven that drilling with a DPD is technically feasible and efficient. It resulted in a higher ROP (72% increase) th an conventional drilling technique [19].…”

“…Therefore the oscillation periodically restricts the fl ow through the passage and creates pulsations in the flow and finally a cyclical fluid ha111l11er effect occun; to vibrate the housiug aml the drill bit during usc. Another example is a Down-hole Pulsating Device (DPD) which was investigated by Nagib et al [19]. When optimizing a drilling system , 4 different p arameters would be considered: bit selection, rotary spe d , WOB , and hydra ulic system.…”

“…[19] found a two-parameter, second degree polynomial to b e considered as the model of the additional jarring force exerted on the bit which was generated by the hydraulic pulsation action. As a result, it was proven that drilling with a DPD is technically feasible and efficient.…”