Technology Update: Drilling Simulation Is Method To Evaluate Incremental Options, Reduce Risk

Abstract

As computing power has become more affordable and the E&P industry's understanding of downhole drilling dynamics has improved, sophisticated simulation software has been developed to optimize drilling. Most drilling engineering analysis software has been based on using static analysis assuming steady-state conditions. Although useful, the end result was little more than a snapshot of anticipated forces. Advanced sensors in the bottomhole assembly (BHA) and improved surface sensors now provide digital measurements of weight on bit (WOB), rate of penetration (ROP), torque, and vibration as a function of time. As a result, it is possible to develop and validate more-complex and -accurate drilling models. Drilling simulation can now provide access to any one of the thousands of nodes presented by means of mesh software rather than by means of static analysis. The i-DRILL drilling simulation from Smith Technologies is an example of this functionality. The opportunity for detailed scrutiny of data leads to understanding normal, tangential, and axial loads that affect system behavior. Since the modeling is based upon the mechanical properties and dimensional data that represent the drillstring and the compressive strength and physical characteristics of the formations drilled, the results are specific to the application and are detailed in terms of what is required to improve performance. Within the virtual environment, the bit type/style, the individual BHA elements and their relative placement, the drillstring, the operating parameters, and the drive and/or steering mechanism (e.g., positive-displacement motor, rotary-steerable tool, turbodrill) can be varied to identify the optimum combination. Bit durability (dull condition), ROP, and stability are considered and weighted. For example, if in a deep well, long trip time is to be avoided at the expense of all other areas of investigation (ROP, vibration, or stability), these may become less important in determining the optimum system. Typically, problems previously encountered while drilling offset wells and other operator experience in the area lead the engineering team to the most important areas of investigation first. Bits and BHAs are methodically tested and retested through the virtual simulation regime, eliminating the poorer performers until the best match and highest normalized score are found. Once these elements are identified, the targets are quantified and weighted according to the economic and strategic (reservoir) project drivers. Once the "best" system is selected from all the options analyzed, dynamic simulations are prepared to visually compare the best vs. worst performance across a variety of drilling dynamics including torque, contact forces, and bending moments. This process works with optimization-matrix and weighting-factor methodology by eliminating guesswork, providing organized engineering data and calculations upon which results and interpretations are based, and providing the sensitivity plots that describe the relationships between ROP, lateral acceleration, and the surface-controlled WOB and rotational rate.