An MWD Downhole Assistant Driller

Abstract

Identification of drilling problems is most commonly achieved by simple comparisons of surface and downhole time-averaged measurements of weight and torque, or by shock and vibration sensors located either downhole or at the surface. Various drilling phenomena are more complex than can be described by these simple shock and vibration measurements. The interpretation of drilling vibration data collected at the surface requires specialized expertise, and can be difficult. Sometimes downhole phenomena are not interpretable at the surface. The diagnosis of bottom hole assembly (BHA) vibrations measured directly by a downhole tool is much easier. A prototype downhole assistant driller measurement-while-drilling (MWD) device has been constructed that unambiguously diagnoses drilling phenomena from sensors that are located in the BHA, and that are sampled at a high frequency. Processing algorithms programmed into the prototype identify bit bounce, stick-slip, backward rotation, torque shocks, BHA whirl, pressure anomalies and excessive stress. Drilling efficiency and specific energy at the bit are also calculated. Average weight and torque values as well as drilling diagnostics are transmitted to the surface and enable the driller to make real-time improvements to the drilling process in a timely manner. A key requirement for enhancing drilling performance is the ability to simply and clearly display information about the drilling process on the rig floor. The prototype display not only informs the driller about the severity of drilling phenomena, but also provides advice about how to eliminate particular drilling inefficiencies before they become problematic. The real-time drill floor display effectively completes the loop between the MWD prototype in the bottom hole assembly and the driller's controls. Additional displays and logs permit the post-drilling assessment of data from previously drilled intervals. The downhole assistant driller helps optimize the rate of penetration, and reduce bit, motor, MWD and other BHA component failures. Downhole drilling parameters, together with quality conventional surface measurements, identify drilling problems and help drillers better decide when to make short wiper runs, or when to trip for a bit. A method for closed-loop drilling operations is presented. This paper reviews the test program and draws conclusions from long term research with both downhole and surface drilling measurements. Actual field results demonstrate how downhole measurements provide a clearer feel for BHA behavior, and allow the driller to optimize the drilling process, reduce BHA component damage, and improve the efficiency of the drilling operation. Background Measurement-while-drilling technology has been used historically to help position a wellbore correctly, and to evaluate the geological formations around the wellbore In addition to having information in real time about where you are drilling, and what you are drilling. it can also be advantageous to have information about how the drilling process is proceeding. When using a hand drill one adjusts the applied force based upon vibrations, sound and reactive torque. Similarly, it is extremely useful to have real-time information from near the drill bit about the wellbore drilling process. The dynamics of bit, BHA and drillstring behavior have been studied both theoretically and experimentally for many years, and there are many publications in the literature. P. 743

Engineering Aspects of LWD Quadrupole Measurements and Field Test Results

“…Understanding these detrimental phenomena and finding ways to avoid them can be the first step towards achieving high quality LWD acoustic, especially quadrupole, measurements. Gravem et al 8 , Hutchinson et al 9 , and Dubinsky et al 10 have demonstrated how an integrated approach utilizing a closedloop drilling control system can drastically improve drilling dynamic conditions downhole and, in turn, the quality of all LWD formation evaluation measurements including acoustics.…”

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