Drilling Efficiently, Durably and Consistently Through Cherts and Conglomerates with PDC Bits is Possible

Abstract

Drilling into harsh environment with heterogeneous formations including chert or conglomerate is usually a boundary that can't be crossed with standard PDC bit technology. This paper will show how an innovative PDC cutter shape combined with a novel 3D approach of cutting structure design have withstood this challenge and successfully replaced 16-in. traditional roller cone application in United Arab Emirates by the latest PDC technology delivering an average 35% improvement on Rate Of Penetration (ROP) while continuously drilling to Total Depth (TD) on each section. When drilling chert or conglomerate type of formation with a PDC drill bit, uneven load per cutters is detrimental to their integrity and results in short runs or brutal stop in the drilling operation triggering a trip for drill bit change. The new technology shown in this paper includes a unique hybrid combination of cutter shapes with a design arrangement of the cutting structure to allow for the pre-fracturing of any hard formation heterogeneity by 3D shaped cutters while standard cutters ensure a high level of cutting efficiency through their shearing action. This innovative concept has been intensively tested in the lab through single cutter and full bit scale drilling testing. In addition, in-house 3D bit simulation software has been used to optimize the cutting structure and assure performance within a wide range of drilling scenarios. Based on these simulations, an optimized design was manufactured for 16-in. directional applications usually tackled by roller cone drill bits and known for having heterogeneous cherty formations to drill throughout the end of the 5,000 ft section. Simulation results helped to validate the unique shaped cutters placement on the cutting structure to maximize the pre-fracturing effect. This design was run on Rotary Steerable System (RSS) and Positive Displacement Motor (PDM) assemblies and successfully drilled 5 wells in a challenging field of the United Arab Emirates offshore operations. 100% successful rate to reach TD in one run was achieved while increasing drastically the average ROP of the section by at least 35%. Moreover, the unique design configuration allowed to better control the directional behavior of the drill string, which resulted in a significant reduction in the overall cost per foot. A new boundary has been breached in several wells of a complex 16-in. chert and conglomerate application in the United Arab Emirates thanks to a years-long effort combining an innovative cutter technology, an optimized bit design process including a state-of-the-art 3D simulation software with lab and field experimental testing campaigns. By looking at the micro level structure of the rock destruction mechanism, a huge improvement has been obtained at the macro level of drilling operation economics.