Analysis of Spiraled Borehole Data using a Novel Directional Drilling Model

Abstract

This paper describes the application of a directional drilling model to wellbore spiraling and compares it to field data. In this paper, the spiraling tendency of a Bottom Hole Assembly (BHA) is determined from a stability analysis of the delay differential equations that govern the propagation of a borehole. These propagation equations are derived from a novel mathematical model, constructed by combining (1) a bit/rock interaction law, which relates the forces acting on the bit to the penetrations of the bit in the rock per revolution; (2) kinematical relationships, which link the bit motion to the local borehole geometry; and (3) a model for the BHA, which expresses the forces and moments at the bit from the external loads and the deflections imposed by the stabilizers. Spatial delays associated with the positions of the stabilizers account for the feedback of the borehole as the stabilizers interact with the wellbore. The analytical form of the propagation equations makes it possible to carry out a stability analysis and determine whether borehole spiraling is expected. The coefficients of the propagation equations embody the characteristics of a particular drilling system; these include the BHA configuration, bit properties, and the active weight, Wa, a calculated reduced weight on bit that depends on the actual Weight On Bit (WOB), the cutter wearflats, and the rock strength. If the bit trajectory is unstable, then any perturbation in the borehole geometry is amplified gradually, eventually leading to the generation of a spiraled hole. The stability of the bit trajectory essentially is controlled by the magnitude of a dimensionless group relative to a critical value that depends on the BHA configuration. This group is a function of the lateral steering resistance of the bit, the bit wear, the rock strength, and the WOB. Thus, a BHA can be either stable or unstable depending on the selected bit, its state of wear, and the WOB. Predictions of the stability analysis are compared with field data from spiral holes pertaining to eight sections from four wells drilled with different bit types and BHA configurations. The paper shows that the propensity of a BHA to spiral can be predicted by the model by assuming reasonable values for parameters such as the lateral steering resistance and the part of the WOB transmitted by the cutter wearflats. This comparison suggests that the model can be used to optimize BHA designs and critical WOB levels that will mitigate the creation of spiral holes.

Robust output‐feedback control of 3D directional drilling systems

“…This parameter is present in the process due to its 3D nature, and it is considered uncertain, since it is affected by the orientation of the bit (which is generally not known) and by the so‐called borehole over‐gauging (see the work of Chen et al). It has been shown in the works of Marck et al, van de Wouw et al, and Perneder and Detournay that these two parameters are key to the stability of the borehole evolution and that they are closely related to the borehole spiraling phenomenon, which we aim to avoid by control in this paper.…”

“…In order to facilitate controller design, a state‐space representation of the dynamical model of the borehole evolution is introduced. Without loss of generality, it can be assumed that a two‐stabilizer system captures the key dynamics of the process (see the work of Marck et al). Then, for this two‐stabilizer case, the states of the system can be defined as This state definition also aids in simplifying the model description since the terms in (1) involving distributed delays are embedded in the states in , which yields a system description with only point‐wise delays.…”

“…The directional drilling process is nowadays still governed by experienced human drillers, which are in charge of manipulating the RSS actuator to control the orientation of the bit and, therefore, the borehole evolution. Experimental evidence has shown that state‐of‐practice directional drilling techniques can induce borehole oscillations . These oscillations in the borehole geometry are undesirable as they (i) compromise borehole stability, (ii) reduce drilling efficiency, (iii) make it more difficult to insert the borehole casing in preparation for production, and (iv) reduce the rate of penetration (ie, the speed of the drilling process).…”

“…The main contribution of this work is the development of a controller design strategy for 3D drilling systems, which relies only on local measurements of the orientation of the BHA. The proposed control strategy is based on the borehole propagation model in the work of Perneder, which has been shown able to capture the key dynamics of the process …”

Modeling contact of pipes within elliptic and spiralled wellbores using finite element analysis

“…These two wellbore types have been selected in this study since they are representative cases encountered in the field. To be more clear, breakouts in certain formations might result in oval or elliptical looking cross sections [11], whereas spiralled wellbores might be drilled due to nature of the drilling mechanism in use [12].…”