Optimal BHA Design for Steerability and Stability with Configurable Rotary-Steerable System

Abstract

There have been significant attempts to optimize the various bottom-hole assemblies (BHAs) used in rotary steerable (RS) applications because the optimal RS assembly can provide operators with significant cost savings by providing less vibration, high BHA stability, high-quality borehole, and thus predictable steerability. This paper presents the development of BHA analysis models using simplified mathematical equations. RS BHA optimization process is demonstrated through the extensive field test program. The predictions of BHA response and directional drilling performance of the RSS have been examined with the numerous field test data taken in a controlled and non-commercial environment, allowing single step changes in both the drill bit features and RS configurations. The testing is unique since the specific rotary-steerable system (RSS) works in field-configurable point-the-bit and push-the-bit modes. Between two distinct RSS operation modes, consistency in stiffness, weight, force applying capability, and control system lead to a direct comparison of different BHA models. Confidential test sites were selected for evaluating different RS BHA configurations in both push-the-bit and point-the-bit modes. The systematic BHA testing was conducted in two different test facilities in North America. A unique sensor system, integrated into the specific RSS, provided real-time measurement of near-bit borehole caliper and near-bit stick-slip and vibration 1,2. This feature allowed real-time evaluation of bit and BHA stability and borehole quality while the maximum build-up test was performed. After each test run, memory data was retrieved and used for more detailed assessment of bit and BHA performance. BHA configuration tests were systematically conducted in a controlled environment so that the relationship between BHA analysis models and actual BHA behaviors could be identified. As a result, the systematic testing and verification lead to the optimal RS BHA design in both push-the-bit and point-the-bit configurations for stability, steerability and borehole quality. Introduction The introduction of the commercial RSS in the 1990s revolutionized directional drilling 3,4,5. Since then, the rotary-steerable system (RSS) technology has remarkably advanced. Today, RSS has become a mature technology, and it is used in a wide variety of directional drilling applications. As such, the driving principles and mechanisms used in commercial RSS have diversified. There are two major schools of RSS design: push-the-bit and point-the-bit configurations. A push-the-bit RSS applies a side force to a bit with multiple expandable steering pads right above the bit, whereas a point-the-bit RSS generates a deflection angle between the low-end tool axis and the borehole axis. There are advantages to both systems, depending upon the application. The following section provides a short discussion of push- and point-the-bit RSS.

Prediction Model of Build Rate of Push-the-Bit Rotary Steerable System

“…eoretically, although the lateral force of the bit can be determined by a series of mechanical models, the magnitude of the lateral force is obtained through the inversion of the drilling data in actual drilling. In addition, the lateral force of the bit is not only determined by the mechanical force of the bit but also related to the parameters of the wellbore geometry [20,21], differences of the bit structure, formation anisotropy, and formation mechanical properties. At the same time, the lateral cutting capacity of the bit, the wear situation of the bit, and the expansion of the wellbore also greatly affect the prediction of the lateral force of the bit with the continuous adjustment of the tool face.…”

A Powerful Build-Up Rate (BUR) Prediction Method for the Static Push-the-Bit Rotary Steerable System (RSS)

“…The 2# stabilizer can decrease the stick-slip vibration of the drill string to protect the MWD system. A variety of methods can be adopted to establish the RSBHA mechanical model, including the finite element method [12,13], the weighted residual method [21], and the beam column method [22,23]. The beam column method is relatively simple and more accurate as compared to the abovementioned methods and has been employed in this paper.…”

“…During the course of wellpath control, the key task is to predict and adjust the BUR to hit the target. The existing BUR prediction methods mainly include the three-point circular method (TPCM) [9,10] and its modified methods [11][12][13], the equilibrium curvature method (ECM) [14] and its modified methods [15], and the equilibrium tendency method (ETM) [16,17]. The TPCMs only consider the geometric configurations of the BHA.…”

“…are the shear forces corresponding to the right end of the fourth beam (left side of the upper step) and the left end of the fifth beam (right side of the upper step), respectively. According to the beam column theory [24], the supplementary equations were derived and showed by Equations (12) and (13). Here, M i (i = 2~5), y 3 , and y 4 are unknown values; y 3 and y 4 contain the additional values ∆ 3 and ∆ 4 , respectively.…”

Dynamic characteristic analysis on the bit lateral steering force of push-the-bit rotary steerable bottom hole assembly

“…With the near-bit expandable pads extending to the wellbore wall, a lateral steering force is generated on the bit which results in a bit side cutting. The force vector and the geometry offset at pads are two controlled variables in different steering principles [7].…”