Technology Solution Drilling Through Extremely Abrasive Heterogeneous Tight Sandstones

Abstract Drilling hard abrasive rock has been very problematic for oil and gas companies. Sandstone and Siltstone layers, with high Unconfined Compressive Strength (UCS) values, are drilled in single or interbedded layers sections to reach the casing point (CP). One of the challenges is the number of bits needed to reach CP. Significant cost is observed due to the additional days needed to drill the wells. This comes from the tripping time exerted due to early bit wear before reaching target depth (TD). The objective was to introduce a new product while applying efficient drilling practices to increase the drilling interval with relatively high ROP and reduce drilling operations cost. Multiple wells have been drilled in different areas. These wells drilled through hard sandstone and siltstone lithology. The common belief in the industry is to use PDC bit with continuous shearing mechanism. The theory states that the rotation mechanism of the PDC cutters ensures that the bit stays sharp for a longer time which allows it to drill further in the sandstone environment. High cost has been encountered by deploying 4 to 8 PDC bits per well to reach the section TD. Hole problems such as under-gauge section, bit junk in the well, twisted off/parted Bottom Hole Assembly (BHA) are major issues in this application. Vertical mapping of high UCS stingers for ongoing sections is difficult due to deposition sequence. Ensuring optimum parameters implementation, performing assessments for pre-run, ongoing run and post run play essential role to benefit from this hybrid approach. The problem was studies and a new product that combines roller cone and PDC cutting elements was introduced in the same application. Further analysis has been conducted to validate the benefit of the hybrid design. UCS calculations as well as lithology percentage were analyzed to understand the added value of the product introduction. The product was deployed in multiple areas to study the bit behavior. In area of interest A, 4 bits were consumed per well. The new product was able to reduce the number of consumed bits from 4 to 2. In area of interest B, bits were averaging 200 ft per run. When the new product was deployed, the interval per bit increased to 800 feet, which improved the efficiency by 275%. UCS as well as siltstone percentage was compared to have an apple-to-apple comparison. The data shows higher ROP as well as longer footage achieved while drilling the same siltstone percentage and using the same parameters. Combining the PDC efficient shearing of the formation with the advantage of the roller cone crushing action allows to drill faster and longer intervals while applying efficient parameters. This paper highlights how the hybrid approach can contribute to significant cost reduction, time saving and necessary avoidance of side-track jobs.