Directional wells are playing a larger role in today's drilling industry. With the development of steerable drilling systems, high angle, large displacement wells have become commonplace. The planning of these more complex well paths has created a need for an empirical analysis using previously drilled directional well data to determine the mechanical feasibility of drilling these wells when considering torque and drag, "drillability".
Data from wells drilled on South Pass Block 60 G-Platform in the Gulf of Mexico has been analyzed to develop an empirical method which will accurately predict torque and drag when planning future high angle, large displacement wells. Torque and drag prediction methods previously published (1,2), were based on the determination of the actual friction coefficient from field data. This has been accomplished by either utilizing a computer model and varying the friction coefficient until a match between calculated and measured surface torque values has been obtained or by utilizing MWD-downhole and surface weight-on-bit and torque measurements and calculating the friction coefficient on a foot-by-foot basis. These friction coefficients generally result in much lower torque and drag predictions for planned wells than are actually measured on drilled wells. These lower values may be attributed to the neglect of the effect of dog-leg severities which are introduced in the normal course of drilling or during correction runs. Previous work (3,4) used a survey simulator based on a random number generator, where dog-leg severities were controlled by an arbitrary scale factor which is called a "dog-leg severity factor".
This paper describes a more accurate method of predicting torque and drag by incorporating the effects of dog-leg severities from a survey database into an existing torque and drag simulator, for the design of the ideal well plan.