Effective real time detection of, and remedy for any drill string and bit dysfunctions or induced wellbore instability are a key factor in optimizing the drilling process to reduce the cost per metre. Surface measurements of drill string vibrations were used in the early sixties to develop the "Snap-log" the result was quite a good method to provide real time information on the nature of the formation being drilled. Unfortunately, in many cases, the dynamic behaviour of the drill string system itself created interferences in the signal leading to a certain lack of reliability of the method. With the objective of optimizing the rock destruction process, further works were conducted on drilling dynamics, both theoretical and technological in 1988, a Drilling Dynamics Control Unit (DDCU) was built : it consists of a vibration radio monitoring sub (le dynamtre) located at the top of the drill string, and of a portable cabin, dedicated to data recording and signal analysis. portable cabin, dedicated to data recording and signal analysis. Today, more than 5000 hours of surface dynamic measurements are available, collected from 4 on-shore and deep wells, and 2 off-shore exploration wells one of the latter was horizontally drilled from a semi-submersible platform into the basement, using a powerful top drive system. This paper describes the capacity of the DDCU to identify a number of downhole drilling anomalies including bit bouncing, bit-wear, blocked cones, bit or stabilizer balling, stabilizer hangup, stick slip, backward whirling, axial and torsional resonances of the drill string… Now that their effects are better understood, drilling parameters (WOB, RPM, Flowrate) can be modified in order to cure such dysfunctions in real time, resulting in a substantial gain of drilling efficiency. Summarizing 4 years of field experience, the chief technical contribution of this paper is: 1 - To prove the ability of the surface dynamic measurements in detecting downhole dysfunctions. 2 - To propose ways of reducing or preventing harmful effects of vibrationson the drilling system. 3 - To present a reliable process aiming at a rigorous optimization of the rock destruction in terms of cost per metre. 1 - BRIEF HISTORY Between 1960 and 1973, the Elf Aquitaine drilling research department carried out various investigations on real-time determination of the properties of rock being drilled. These research projects depended on the development of a surface measurement system to monitor the vibrations of the drill string which is assumed to convey information on the hardness of the rock, and a downhole device fulfilling the same role close to the bit; they led to the development of a new kind of log, known as the "Snap-log". As the downhole tool was initially intended to validate surface measurements, it was first necessary to design a wireless downhole/surface transmission system. The design of this transmission system, later developed by Teleco, was at the origin of the first MWD commercial service. Since 1986, the DYNAFOR research project has sought to pursue the exploration of this same research area with the main pursue the exploration of this same research area with the main objective of gaining a better knowledge of the dynamic behaviour of the drill string, a component which is considered to be as fundamental as the rock itself in determining a rigorous approach towards optimizing the drilling process. P. 409
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
Introduction Measurement-while-drilling (MWD) systems have been used historically to position a wellbore correctly and to evaluate geological formations around the borehole. In addition to having real-time information about where you are drilling and what you are drilling, it is also advantageous to have information about how the drilling process is proceeding. The interpretation of downhole drilling characteristics from surface measurements requires specialized expertise and is not always reliable. Placing a downhole MWD device that measures both drilling forces and motions near the bit provides more reliable diagnoses of drilling phenomena. Presenting this information on an easily interpreted rig-floor display permits the driller to "feel" how a well is drilling.
Surface monitoring of downhole vibrations, a promising way to improve drilling efficiency, has been the subject of growing recent interest. While the history of vibration monitoring in Russia has been similar to that of Europe, with an initial focus on the effects of lithology, it was subsequently developed into a solution for problems relating to turbodrilling efficiency, the common approach to drilling in Russia. Elf Aquitaine, in France, commenced work for real-time lithological recognition from surface vibrations in the 1960s; drilling optimization evolved as a further application using their Dynametre. ARCO Oil and Gas Company developed a very similar technology to Elf, focussed initially on reducing premature fatigue failures in the drillstring and bit. All three approaches are now being synergistically combined through cooperation in this area, and contain many identical elements, both in theory and practice, which highlight the basic common physics of these measurements. Field examples of each approach, and practical applications of this technology are presented. A combination of all of the above techniques will improve the contribution made by surface vibration monitoring to drilling optimization.
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