Deployment Of An SeROP Predictor Tool For Real-Time Bit Optimization

Abstract

Abstract Since 1965, specific energy (SE) principles have been used to predict bit performance and analyze rate of penetration (ROP) and bit efficiency (1). Factors that create drilling inefficiency include bit dull, bit balling, bottomhole balling/cleaning issues, torque/drag, and drillstring vibrations. These are often evident with high SE values. Based on these principles, Chevron has established proprietary relationships for bit-specific coefficient of sliding friction and mechanical efficiency as a function of the rock's confined compressive strength (CCS). Chevron then uses these relationships to predict reasonable and achievable ROPs with the associated bit torque for several bit types most commonly used in their global operations. The effect of mud weight, blade count, and cutter size to the coefficient of sliding friction and efficiency are considered in the ROP predictions (2). These relationships have proven to be of high value in the creation of a globally accurate drilling tool for improving overall bit performance and reducing well costs. Applied real time, the tool identifies inefficient drilling conditions and provides operations personnel with the reliable information needed to make more informed decisions and achieve the best possible performance out of the bit that is in the hole, as well as quantify the impact of parameter changes. This paper will present a number of global case histories showcasing Chevron's rapid deployment of the Specific Energy Rate of Penetration (SeROP) Predictor Tool to maximize its value and reduce drilling costs. These case histories used evolving strategies, which varied according to the well's complexity and the wellsite resources available. Also shown are the incremental benefits gained when bit performance prediction/selection modeling was coupled with real-time down-hole measurements. The paper also presents the limitations and increased data requirements that are required for complicated wellbore geometries. Introduction Throughout the well construction process there are clear opportunities to reduce costs by increasing reliability and productivity. However, it is often difficult to quantify a number of other costly, seemingly invisible, efficiency opportunities. These include opportunities such as determining if the maximum ROP for the formations encountered is being achieved, maintaining a stable operating environment to optimize bit longevity, and knowing when or how to improve conditions when performance is sub-optimal. Chevron's rock mechanics efforts and proven strength in formation characterization have driven the development of the SeROP Predictor Tool to quantify and reduce the invisible lost-time component of drilling and tripping costs. This is accomplished by: The most important component of the SeROP Predictor Tool is the incorporation of CCS, which differs from existing ROP analysis and prediction methods that are based solely on unconfined compressive strength (UCS). UCS predictions are problematic and erroneous because UCS does not represent the "apparent" strength at the rock-bit interface. CCS is defined as the increased compressive strength of a rock from the pressure differential between the borehole pressure and the formation fluid pressure. CCS better represents the "apparent" rock strength in overbalanced drilling environments (2).