A Fundamental Model for Prediction of Hole Curvature and Build Rates W ith SteerableBottomhole Assemblies

摘要

There are four key technical issues to be addressedrnwhen drilling directional wells with steerable bits andrnbottom hole assemblies: maximizing hole quality,rnaddressing tool face control, eliminating bit andrnassembly vibration, and predicting hole curvature orrnbuild rates. Hole quality 1 and tool face control 2-7 havernbeen covered in several previous SPE papers, as has bitrnand assembly vibration elimination 8-9 . This paper coversrnthe recent development of a fundamental model for thernprediction of hole curvature based on measured bitrnresponse and modeled bottom hole assembly behavior.rnBit side cutting is a nonlinear function of side force,rngauge design, rotary speed, rate of penetration, rockrnstrength, and cutter dull state. To characterize the bit'srnside cutting response, a series of tests are run in a fullrnscale drilling simulator under a variety of drillingrnparameters and sideloads. Axial and lateral bitrntrajectories are measured and a response curve isrngenerated. The bit side cutting angle measured in thernlab, is equivalent to bit tilt calculated on a bottom holernassembly (BHA). Several hundred tests have been runrnto measure the response of numerous bits. Thesernresponse curves are then used to relate bit performancernto BHA response.rnThe BHA is modeled with a finite element analysisrnprogram over the range of hole curvatures and toolrnsettings which define the operating envelope for the tool.rnThe result of the analysis is a bit side force to bit tiltrnresponse surface for the tool over its operating range.rnThe response curve for the bit and the response surfacernfor the BHA are then plotted on the same set of axes.rnThe intersection of the two graphs represents the steadyrnstate response of the system and is used to predict thernachievable hole curvature of the bit-BHA system. Thisrnwork shows that bits often selected for rotary steerablernsystems are more laterally aggressive than required ofrnthe BHA to achieve the desired hole curvature.rnThe model has been verified with full scale field tests.rnWhile this work was originally developed for PDC bitsrnand rotary steerable systems, the fundamental modelrncan be applied to all types of bits and drilling systems. Itrnhas also been applied to motor and vertical drillingrnsystems with PDC and Impregnated bits.