Surface Detection of Vibrations and Drilling Optimization : Field Experience

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

Modeling and Analysis of Axial and Torsional Vibrations of Drillstrings with Drag Bits

“…no lateral vibration), is obtained by integrating the action of a single cutter on the bit profile. The total torque on bit (TOB) and weight on bit (WOB) account for the sum of cutting terms acting on the cutting faces of an equivalent cutter and an friction term at the all wear flats/rock interface as fc WOB WOB WOB  fc TOB TOB TOB  (10) The cutting components of the Torque On Bit (TOB) and Weight On Bit (WOB) are independent of bit cutters arrangement and the bit shape that can be written as:…”

“…Stick-slip vibrations are related to the torsional vibrations where bit passes through periodically two phases: sticking (the bit stops rotating) and slipping phases (the bit is released from sticking phase with angular velocity higher than nominal velocity). It has been documented that for about 50% of the on bottom drilling time the drill bit experiences stick slip vibrations [10].…”

Drill monitor with strata strength classification in near-real time.

“…A roller cone bit is used in drilling for oil. The vibrations of the drill string have been utilized, via a wireless transmission system, to refine control of the drilling process (Henneuse 1992).…”

Practical approach to modelling and controlling stick-slip oscillations in oilwell drillstrings

“…14-805, 07730 Mexico, D.F., Mexico enavarro@imp.mx R. Suárez is also with the PIMAyC-IMP rsuarez@imp.mx not for its amplitude, but due to its cyclic nature. Indeed, stick-slip appears during the 50% of drilling time [3], [8], [13]. In addition, the whipping and high speed rotations of the bit in the slip phase can generate both severe axial and lateral vibrations at the bottom-hole assembly (BHA).…”

“…In addition, the whipping and high speed rotations of the bit in the slip phase can generate both severe axial and lateral vibrations at the bottom-hole assembly (BHA). Four main kinds of problems can be originated from these vibrations, such as: (i) drill pipe fatigue problems [13] (causing drillstring connection failures); (ii) drillstring components failures [13], [19]; (iii) wellbore instability [23]; (iv) bit damage [8], [17], [18], [19], [29]. Although the effect of stick-slip vibrations is more significant in bits with polycristalline diamond compact cutters (PDC bits), recent studies have addressed the harmful consequences of torsional, axial and lateral vibrations in roller-cone bits [5].…”