Drilling Optimization Using Model-Based Design and Stratigraphic Zonation: Successful Application in Brazilian Deep Water Pre-Salt Carbonate Reservoir

Abstract

Abstract After findings were made in the pre-salt province that represented a major discovery for the oil industry, drilling activity in Brazil has been focused primarily on economically viable ways to develop these reserves. The pre-salt cluster is a geological formation that consists of organic microbial carbonates and other sediments. The reservoir poses innumerous drilling challenges, including hard silicate nodules and low-porosity layers, which make the formation strength extremely high. Also, the heterogeneity level of such carbonates (within centimeters) imposes extra challenges, especially on drilling shock & vibration, with low rates-of-penetration (ROP), raising pre-salt well construction costs. To offer a technical solution, the service provider applied an innovative approach based on two pillars: a model-based design approach, leading to two drill bit designs with improved cutting structure resistance, with dynamic stability, delivering the entire section in one bit run with higher ROP. Along with the technology, a new workflow called "stratigraphic zonation for drilling" was implemented. This paper reviews the work covering this new stratigraphic zonation workflow, the development of this virtual drilling scenario and some field results with lessons learned and way forward.