Predicting Bottomhole Assembly Performance (includes associated papers 17015 and 17075 )
- J.S. Williamson (Smith Drilling Systems, Div. of Smith Intl. Inc.) | A. Lubinski (Consultant)
- Document ID
- Society of Petroleum Engineers
- SPE Drilling Engineering
- Publication Date
- March 1987
- Document Type
- Journal Paper
- 37 - 46
- 1987. Society of Petroleum Engineers
- 1.6.6 Directional Drilling, 1.6.2 Technical Limit Drilling, 1.4.1 BHA Design, 1.12.1 Measurement While Drilling, 1.10 Drilling Equipment, 1.12.6 Drilling Data Management and Standards, 1.11.2 Drilling Fluid Selection and Formulation (Chemistry, Properties), 1.10.1 Drill string components and drilling tools (tubulars, jars, subs, stabilisers, reamers, etc), 4.3.4 Scale, 1.5 Drill Bits, 1.6.1 Drilling Operation Management, 5.3.4 Integration of geomechanics in models, 1.6 Drilling Operations
- 3 in the last 30 days
- 547 since 2007
- Show more detail
- View rights & permissions
|SPE Member Price:||USD 5.00|
|SPE Non-Member Price:||USD 35.00|
Summary. A computer program for prediction of bottomhole assembly (BHA) performance has been developed. Input parameters include formation dip performance has been developed. Input parameters include formation dip angle, hole and collar size, and stabilizer spacing. The predictions are in drilling terms: hole curvature, hole angle, weight on bit (WOB), etc. Results of extensive parametric studies and field use are presented.
Poorly designed BHA's restrict the WOB, thus increasing Poorly designed BHA's restrict the WOB, thus increasing cost. A BHA computer program, BHAP, has been developed to predict performance and has been used extensively in conducting parametric studies and in making field decisions for the best performance. The program takes into consideration formation characteristics, any number of stabilizers, drill-collar (DC) sizes, square collars, shock absorbers, motors, directional tools, and measurement-while-drilling (MWD) tools. Predictions are given in drilling terms, such as rate of building or dropping angle in degrees per 100 ft [0.57x 10-(3) rad/m]. The simplicity of the mathematical model-two-dimensional, constant hole curvature, static-results in manageable computer time, which is vital for field use.
It is well known that dipping formations generally result in high hole angles. Several papers on the effect of bit/ formation interaction on deviation have been published. Refs. 1, 3, and 4 are based on the mechanism of a single wedge or tooth, and not the bit itself. Application of these models to a three-cone bit would be extremely difficult. Models for polycrystalline-diamond-compact bits are more feasible, but expensive because of computer time. In most of these papers, the bit/formation interaction is not coupled to the BHA. Similarly, most of the publications dealing with BHA computer programs (Refs. 7 publications dealing with BHA computer programs (Refs. 7 through 17) do not include any bit/formation interaction. Therefore, the output is the lateral force on the bit and the direction in which the bit points, but not the parameters of greatest interest, such as hole angle and rate of parameters of greatest interest, such as hole angle and rate of change of hole angle.
To predict the performance of BHA's in field-usable terms, the effect of the formations must be included. One paper attempts this by postulating that dipping formations paper attempts this by postulating that dipping formations impose a bending moment at the bit. 18 Another supposes the existence of geologic forces 16 that push the bit updip. We believe that (1) drilling in the direction of the force on bit occurs only in nonsedimentary formations, such as granite; (2) drilling is not in the direction in which the bit points; (3) bending moment at the bit is zero; and (4) force on bit depends on only the mechanics of the BHA, not the formation.
To account for updip drilling, drillability in the direction perpendicular to bedding planes is considered greater than in the direction parallel to bedding planes. This has been confirmed by laboratory experiments. The ratio of the two drillabilities is related to the so-called formation class. Thus formation crookedness depends on both the formation dip angle and formation class, Fc (see Eqs. A-1 through A-3). Such a model is simple. A more complicated model is not warranted because of the lack of precision of input parameters, such as hole gauge and stabilizer clearance. For an isotropic formation, Fc = 0. For a very anisotropic formation, corresponding to Formation Class A in Ref. 23, Fc = 100. (See Bit Anisotropy in the Appendix.)
The following parameters are entered: hole size; hole angle. dip angle; formation class; mud weight; WOB, DC information; and stabilizer(s) information, including clearance(s), bent sub, or other directional-tool information (if any), and hole curvature (assumed constant)-i.e., degrees per 100 ft [0.57 x 10-(3) rad/m]. All these parameters should be known, except one-the unknown. parameters should be known, except one-the unknown. Noncylindrical cross sections (square collars) or tools with reduced stiffness-such as shock absorbers, motors, and MWD tools-may be modeled.
As an example, the following is used to model square collars: (1) OD is taken as the distance across the corners, (2) ID is chosen to model the moment of inertia, and (3) the density is chosen to model the weight per unit length.
Prediction of Performance Prediction of Performance To be successful in the application of BHAP in the field, we first conducted extensive parametric studies. These studies provided basic understanding of field phenomena. The following hypothetical cases are presented to show phenomena. The following hypothetical cases are presented to show the need for dip information and how BHAP may be applied.
|File Size||871 KB||Number of Pages||13|