Saving 2.2 Days from Drilling in Hard and Abrasive Sandstone Formation with Innovative 360 Rolling Diamond Element Bit Technology

This project drilled in Sin Phu Horm field. The main challenge in this field is the formation. The 8.5-in section is designed to drill through the hard and abrasive sandstone formation (known as Nam Phong formation) with unconfined compressive strength (UCS) between 6,000 and 24,000 psi and peak up to 55,000 psi. Multiple bit runs and heavy set of Polycrystalline Diamond Compact (PDC) bits were observed in the offset wells with slow rate of penetration (ROP) and short intervals, which resulted in a high drilling cost. In the offset runs, the average interval was observed between 200 and 300 meters and average on-bottom ROP ranged from 2 to 8 m/hr. Worn cutters were the main dull characteristic in the offset PDC bits and the bits were pulled out of hole due to slow ROP. Due to the challenging formation, the goal was to increase the interval per bit run and ROP which resulted to reduce the number of bit trips and drilling cost. Looking at the dull grading of the offset PDC bits, it was obvious that the slow ROP was caused by the cutters worn by the abrasive and hard Nam Phong formation. The fixed-cutter PDC bits were run in the offset wells and worn cutters were observed in the shoulder area. The worn portion of the cutter occurred only in the exposed side, while the portion in the cutter pocket remained intact. Utilizing the portion in the cutter pocket helps to prolong cutter life, increase the ROP, and bit life longevity. Thus, it can help to reduce undesired bit trips. Based on the worn cutter observation, the new design of the 8.5-in PDC bit equipped with innovative 360 rolling cutter (RC) bit was proposed. A comprehensive vibration simulation drilling parameters roadmap were provided to minimize shock and vibration. Two bits were run with rotary steerable BHA to drill Nam Phong formation in the field. The first bit drilled 431 meters at an average ROP of 6.8 m/hr and the second bit drilled 391 meters at an average ROP of 5.5 m/hr. Two runs using the 360 RC bits drilled 822 meters in total of 1,236 meters entire interval of Nam Phong formation, which was equivalent to 66%, achieving the operator's goal while saving 2.2 days solely from two runs of RC bit. This success increased the operator's confidence to run 360 RC bits in the subsequent wells to reduce the number of bit trips and increase the ROP. This paper will discuss the application and evolution of 360 RC bit, along with the result achieved by the bit fitted equipped with this cutter in Thailand onshore.

An Analytical Approach to Cutter Edge Temperature Prediction in Milling and Its Application to Trochoidal Milling

Cutter edge temperature in milling is an important factor to cutter life. With high cutting speed and feedrate, the cutting efficiency is high; however, the cutter edge temperature is high, shortening the cutter life. Therefore, it is necessary to know the cutter edge temperature in milling. Unfortunately, the cutter edge temperature is difficult to measure and predict in milling. To address the technical challenge, an analytical approach was proposed to predict cutter edge temperature in milling. First, the heat flux into the cutter edge was calculated. Second, by using the Green function, the cutter edge temperature was figured out, and the results obtained from this approach agreed well with that of a recognized test. Then, based on the engagement between the cutter and workpiece in trochoidal milling, the cutter edge temperature was obtained in trochoidal milling. Finally, a temperature comparison was made between trochoidal and side milling based on this analytical approach, and the reasons that trochoidal machining could extend the cutter life were found. This approach is first proposed to calculate the cutter edge temperature in trochoidal milling and can be applied to machining parameters optimization in trochoidal milling and cutter design optimization.