Accurate Real Time Drill Bit Wear Prediction by Combining Rock Energy and Drilling Strength Concepts

In today’s drilling operations there is a constant push for drilling cost reduction. A central element to reduce cost is to improve drilling operation by analyzing real-time data. To do so, advanced real-time analysis tools needs to be developed. Two approaches currently in use for optimizing the actual rotary drilling process are Mechanical Specific Energy (MSE) and inverted ROP models. MSE is calculated as the work needed to destroy a given volume of the rock. It can act as tool during drilling operation to detect change in drilling efficiency thus providing a method to optimize the drilling parameters to enhance ROP. ROP models, on the other hand, can be used to calculate formation drillability with considering the effects of drilling parameters; bits design and bit wear. Drilling optimization using ROP models is then done by changing the drilling parameters or bit design. In this project wells from offshore Middle East is analyzed by comparing MSE and drillability. Formation MSE and drillability are comparable for individual bit runs. However, they differ when the mud weight is changed and they deviate when bits are worn. These two differences are due the fact that MSE does not include bit wear as well as mud weight effects. To overcome the model constraints we combined both methods and modified the MSE equations to be able to incorporate these effects and use MSE as a real-time trending tool for Bit wear estimations. The field results are very encouraging in that the Bit wear for both Rollercone and PDC bits can be predicted with good accuracy. The field application of this new approach is that a sound decision can be made regarding the pulling of bit while it is in the hole during drilling and improving overall economics of the drilling operation.

Keywords:

Mechanical Specific Energy , Rate of Penetration Model , Rock Drillability , Drilling Optimization , Fractional Bit Tooth Dullness , Bit Dull Grade State