Drilling activity in Brazil has been focused primarily on developing offshore oil reserves in the high-profile pre/post salt plays. However, test wells in the Sao Francisco basin in the central state of Minas Gerais, have identified a vast opportunity for onshore natural gas production from unconventional tight sandstone and carbonate formations. The prospect is attractive because of its relatively shallow depth that varies from 2000 to 4000 meters and its close proximity to high population density. These gas rich formations present an important mixture of medium to hard lithologies that are at the same time highly dipped and faulted. This represents a great challenge for the drilling engineers and service companies while trying to maintain the verticality of the well and drilling at a competitive rate of penetration (ROP). During the last two years drilling activities in the basin have intensified as the need for an abundant source of energy becomes more evident. This necessity is directly proportional to Brazil's economical surge in the last decade. The invigorated economy is consuming more goods and energy and the existing traditional ways of powering the economy might no longer be sufficient. The answer appears to be natural gas, already proven to be abundant in the area but held captive in super tight formations. When oil companies were approached, they set for their main objective to drill vertical wells into the gas producing formations in the most efficient manner as possible. In Brazil's land drilling activities, economics are crucial due to the characteristics of the oil and gas companies and the high number of wells needed to produce at commercial levels. Since then, the operating companies have experimented with several drilling technologies attempting to extract the hydrocarbons at an economic level. Field trials include impregnated bits on turbines, hybrid bits, fluid/electromagnetic hammers and high speed motors (PDM) and rotary steerable tools (RSS). All BHAs met the goal with limited success and two major issues, lack of ROP and hole deviation problems. To solve the daunting challenges, the service company recommended drilling with nitrogen/air and hammer bits to increase ROP and maintain hole verticality to reduce/eliminate expensive correction runs. This way more wells could be drilled cheaper and much faster. As a result of this under balanced drilling approach, two wells were successfully drilled with percussion hammers which enabled the operator to maintain verticality from top to bottom with less than 5° deviation and at a much higher rate of penetration. This increased performance, in addition to the better control of verticality allowed for a reduction of total drilling time and translated to reduction in total well cost. The time to drill the two wells with air took approximately 30 days (wells to 1500-2000m), whereas in the other group of wells in the basin with conventional methods, the average time was no less than 50 days, depending on the area of the basin and targeted TD.

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.

After 10 years of Brazilian presalt exploration and development, the carbonate reservoirs continue to pose drilling challenges, leading to unwanted bottomhole assembly (BHA) trips due to severe shock and vibration, low rates of penetration (ROP), and premature drill-bit cutting structure damage. Today, industry efforts to improve the performance in the Brazilian presalt carbonates are driven by trial and error, which is very costly in the ultradeepwater drilling environment. The adoption of a collaborative mindset since 2012 between a service provider and operator with the desire to bring about a step change in drilling efficiency on the Brazilian presalt cluster enabled a systematic learning framework to capture, evaluate, and reuse knowledge from drilling dynamics, geological, and petrophysical aspects. The innovation of this work is the implementation of an improved, fully digital bit design workflow, integrating calibrated 4D dynamic simulation model and petrotechnical expertise from drilling engineering, geomechanics, geology, and petrophysics groups to continue to push the drilling performance envelope in the challenging Brazilian presalt application.