Surface Detection of Vibrations and Drilling Optimization : Field Experience

Abstract

Abstract 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