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Dr. Alvaro Maia da Costa

Department of Mineral Engineering, State University of São Paulo, Brazil, Research Center for Gas Innovation (RCGI) at State University of São Paulo, Brazil, and MODECOM2 (Technology in Computing Mechanics and Geomechanics), Rio de Janeiro, Brazil.

 

Talk Title
The salt rock, “a strategic geomaterial in Brazil”: A history of success

Talk Abstract
 

In the 1960s, the Brazilian government discovered commercial deposits of sylvinite, (KCl.NaCl) in Sergipe State, Northeast of Brazil. From the sylvinite ore, potassium chloride fertilizer is obtained by flotation method, which is an essential input for the Brazilian agro-industry. The sylvinite deposits ranges between 450 m and 700 m in thickness. Despite its great economic and strategic attractiveness to the country, a great technological challenge had to be overcome. The deeper deposits with greater thickness and lateral continuity were overlied by tachyhydrite salt rock, (CaCl2.MgCl2.12H2O). Most salt rocks are subject to the creep phenomenon, which in a simple way is characterized by continuous deformation under constant stress. In the case of tachyhydrite, the creep strain rate is about two orders of magnitude higher than that of sylvinite. Due to the presence of tachyhydrite underlying the sylvinite layer, underground mining is usually subjected to large deformations as a result of excessive creep of the tachyhydrite. In the 1970s, a set of programs based on the finite element method known as COVES programs, specifically formulated to cover all non-linear phenomena of geomaterials, including the creep phenomenon were developed. By 1978, hundreds of rock mechanics laboratory tests were done to accurately determine the mechanical properties of the geomaterials present in the mine/deposit. This significantly improved the governing constitutive equations of the geomechanical model of the geomaterials which were implemented in the computer COVES programs to enable its application in the geomechanical design of the structures in the mine. Back then, the strategy of dealing with the tachyhydrite required an experimental panel to be excavated on the top of the tachydrite layer by implementing the results obtained from the COVES finite element programs. By applying the computing modeling through inverse-analysis of the measurements made in the experimental panel, it was possible to redefine the geomechanical parameters accurately and facilitate the mine’s excavations, though overlied by tachyhydrite. To date, the mine is still operational, producing approximately 500,000 tons per year of sylvinite, with the majority of the mining being carried out overlying the tachyhydrite. More than 35 years after the commencement of the sylvinite mines, one of the largest offshore oil reserve in the world was discovered in the Brazilian coast at the Santos Basin, comprising predominantly of pre-salt reservoirs.  These reservoirs are located in water depth of approximately 2200 meters possessing large stratified halite salt layers (NaCl) which is very difficult to drill due to presence of intercalations of tachyhydrite and carnalite which is the same enigmatic geomechanical salt rocks that had been faced in the potash mine of Sergipe. Fate allowed the implementation  of all experience gained from the successful mining activities in the potash mine to be applied in the exploitation activities of Santos Offshore Basin. The pre-salt reservoir was discovered through wellbore RJS-628, also known as TUPI. The successful discovery well project had adopted the COVES program. The discovered pre-salt giant oil reservoirs in a time span of less than 10 years already accounts for more than 50% of the country's oil production, with production rate ​​above 1 million barrels per day. This was possible because the salt barrier was quickly overcame by implementing past experience gained from the Sergipe potash mine. The COVES program facilitated the design of more than 300 wells in the Santos basin. The oil from the pre-salt reservoirs is of high quality with API gravity of 280 API and GOR of more than 220 m3/m3, that is, for every 1 m3 of oil produced, more than 220 m3 of associated natural gas is also produced. Recently, a new technological challenge involving the disposal of the contaminant CO2 present in the associated natural gas has evolved. The carbon dioxide can not be vented into the atmosphere after it has been separated from the natural gas on the productionplatform. However, the halite salt rock is an important geomaterial that can be exploited to discharge the CO2, due to its favorable characteristics of negligible permeability, self healing ability of fractures induced by the creep phenomenon and ability to withstand high pressures and high temperatures. The execution of giant offshore caverns in the salt layer overlying the pre-salt reservoirs, open by dissolution mining is currently being studied to discard the CO2, thus fulfilling the CCS (Carbon Capture and Storage) function. It is expected that the giant salt caverns studied can store 7.2 million tons of CO2. The salt dome selected can accommodate the construction of 15 caverns, thus, providing the confinement of approximately 108 million tons of CO2.

The lecture would be aimed at discussing the history of studies of computational mechanics and gemechanics that have made possible many strategic ventures in Brazil for over 40 years and provide a platform for extendable applications in other part of the world having similar geological conditions and depositional environment. The target audience for the lecture include: students, faculties and industry professionals interested in geomechanical innovations in mining of salt rocks, ultra-deep offshore drilling through thick salt layers and CO2 abatement and gas storage in salt caverns opened by dissolution mining.

Acknowledgments

The authors gratefully acknowledge support from Shell Brasil Petroleo and FAPESP through the “Research Centre for Gas Innovation - RCGI” (FAPESP Proc. 2014/50279-4), hosted by the University of Sao Paulo, Brazil and the strategic important support received from ANP (Brazil’s National Oil, Natural Gas and Biofuels Agency) through the R&D levy regulation.

Short Biography

Alvaro Maia da Costa, D.Sc. - graduated from department of Civil Engineering, Federal University, Rio Janeiro, Brazil (UFRJ) where he was awarded the Mauricio Joper Award as the best student in soil mechanics in the Class of 1976. He also holds a M.Sc. and a D.Sc. degree in Civil Engineering from the same university, COPPE / UFRJ. In the 70's, he developed computer simulators that have been used for more than 40 years in different projects in the areas of mining, oil and gas exploitation and various civil engineering constructions. He is responsible for the development of new technologies applied in offshore structures and foundations of fixed platforms (obtained a patent), fixed anchorage points of Floating Stationary Production Units (obtained a patent), continental slope stability, pre-salt and sub-salt well design, onshore and offshore HPHT pipelines design (obtained a patent), reservoir geomechanics, platform hulls, risers and lines, underwater equipment foundations, etc. With more than 40 years of experience in the geomechanical behavior of salt rock, he participated in the design of more than 240 wells drilled through salt rock in Brazil and abroad using his own simulators. He is responsible for the sylvinite mining projects at the Sergipe Potash Mine overlying the tachyhydrite rock (an unprecedented case in the world). He is responsible for the study of the stability of caverns opened by dissolution mining for the production of brine in Salgema Mineração. Adviser of several masters and PhD  theses and participated in more than 200 MSc. And DSc. committee. Author and co-author of more than 100 papers in national and international congresses and indexed technical journals. He coordinated the network of excellence in naval and oceanic engineering and is the creator of the Galileo Network of Scientific Computing and Visualization used in 15 Brazilian universities. Member of the Brazil National Engineering Academy, recipient of 2010 SPE Technical Excellence Award, recipient of 5 awards from Petrobras for his inventions and 7 awards from Petrobras for Excellence in Results Presentation.

 
Talk Keywords
Salt rock: sylvinite, tachyhydrite, halite, carnalite; Creep phenomenon; COVES finite element programs; Pre-salt reservoirs; Dissolution mining; CCS.
 
Target Audience
Students, Post doctoral, Industry, Doctors and professors
 
Speaker-intro video
TBA 
 

The International Conference on Innovative Applied Energy (IAPE’18)