Computerized Drilling Control

Abstract

An on-site computer system to control bit weight and rotary speed has been developed and successfully installed on a South Louisiana well. Early field tests indicate that the system could be invaluable in reducing drilling costs. Introduction Previous laboratory and field experimentation has Previous laboratory and field experimentation has demonstrated the effect of several variables on drilling rate. These results have been incorporated into optimization theories for the purpose of reducing drilling cost. Minimum-cost drilling theories rely on a combination of historical data and empirical prediction techniques for selecting optimum bit weight and rotary speed. Past solutions have required extensive use of computing equipment because of both the complexity of the mathematical formulations and the large number of parameters involved. Field attempts to apply these computed results have frequently failed because of the uncertainty of input data requirements. Humble has developed an on-site computer system to control bit weight and rotary speed and thereby implement the concepts of minimum-cost drilling. This system canperform short interval drilling rate tests for formation evaluation,use the results of these tests as input information to solve minimum-cost drilling formulas, andcontrol bit weight and rotary speed in accordance with these computed solutions. The purpose of this paper is to describe the computer control system and present results of initial field testing. Theoretical Considerations Minimum-cost drilling (MCD) requires a quantitative evaluation of the variables involved. Several forms of a basic mathematical model have been suggested. The relationships reported here form the basis for the solution programmed in this work. Four equations are used, expressing drilling rate, bit bearing wear, bit tooth wear, and cost. A solution for minimum-cost drilling assuming constant bit weight and rotary speed over the entire bit life has been programmed for use in computing MCD schedules. This solution is subject to certain limiting assumptions such as those discussed by Graham et al.:Drilling cost is the summation of bit cost, rotating cost, connection cost and hoisting cost.Diamond bits are excluded.Bit life is limited by either bearing failure or tooth wear, or by a combination of operational factors that make it cheaper to pull an incompletely consumed bit.Circulating hydraulics are adequate and do not limit drilling rate.Bit weight considerations exclude hole deviation.Drilling rate is a function of only bit weight, rotary speed, and degree of tooth dullness; that is, the effects of pressure, lithology, fluid property, hydraulics and drill string dynamics are ignored. JPT P. 483

A hybrid fuzzy-PI control model for constant-pressure automatic bit-feeding system of large-diameter shaft drilling rig

“…in 1969. [13] The current widely-used mode (I) is Young Model Amendment (YMA) , amended by his descendant experts .…”

Drilling Variables At Technical Limit Of Drilling Rate

“…(12)(13)(14)(15) Among them, perhaps the most complete mathematical drilling model being used is Bourgoyne and Young's model (21,22) . 8 The functions f 1 through f 3 represent the effect of uncontrollable drilling variables on drilling rate.…”

“…There are two popular analytical models that can be used to produce a table of 'cost per foot' for a range of practical WOB and rotary speeds (12)(13)(14)(15) . They are both used to model penetration rate for tri-cone roller cone bits.…”

“…This is called minimum cost RPM (N MC ). This number and minimum cost WOB can be determined simultaneously (12)(13)(14)(15) . However, before applying minimum cost RPM, the torsional strength of pipes must be investigated.…”

“…Effect Effect of WOB on drilling rate Effect of rotary table speed (RPM) Effect of flow rate on drilling rate Effect of fractional tooth wear on drilling rate Experimentally determined rock failure envelop(15) BHHP per in 2 of Bottom Hole Area, HP Drilling Rate…”