Perforacion

3rd International Conference on Sustainable Development Indicators in the Minerals Industry, June 2007, Milos island, Greece

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Sustainable drilling for oil and gas: challenging drilling environments demand new formulations of bentonite based drilling fluids
V.C. Kelessidis
Department of Mineral Resources Engineering, Technical University of Greece, Hania, Greece

ABSTRACT Demand formultifunctional drilling fluids continuously increases. In the quest for more hydrocarbons, drilling has extended to deep water areas (now in excess of 2.000 m) and to very deep wells (now in excess of 6.000 m). In these extreme conditions, low temperatures, as low as 1-50C on the sea bed, high temperatures, in excess of 200oC, and high pressures, more than 1.000 bars, in the bottom of the well, arefrequently encountered. In these harsh environments, synthetic oil and oil based drilling fluids are used, but the former are expensive while strict environmental requirements have limited the use of the latter. Thus, drilling industry has turned back to water based drilling fluids which use bentonite as primary viscosifier and as a fluid loss control additive. However, in conditions of hightemperatures, bentonite suspensions gel and loose their exceptional low temperatures properties, thus, additives are needed to overcome such problems. In this article we review these challenging drilling environments and establish the requirements for the multifunctional drilling fluids. Our research indicates that demand for continuing use of bentonite by drilling fluid industry is strong.Furthermore, we bring forward the opportunities for new additive development which can expand the operational ranges of bentonite suspensions. 1. INTRODUCTION Bentonite is an essential component for the oilwell drilling industry. World production of ben-

tonite remained high, between 12.5 and 17.5 million tons per year (2002 data, Robinson et al., 2004; Agnello, 2005) with USA producing 44% whileexporting 22%. Greece runs a close third from China, with 1.26 million tons per year, contributing ~ 7.5% to world production (Robinson et al., 2004). Of the many uses of bentonite, the use in oil well drilling fluids accounts for about 25% in USA (USGS, 2005) and about 5% in South Africa (Robinson et al., 2004), countries for which data were publicly available. In Figure 1, the apparent use of bentoniteover the past seven years in USA is shown together with the consumption of bentonite by drilling fluid industry. Drilling fluids are essential elements for the successful drilling of oil, gas, and geothermal wells. Drilling fluids are used to: (1) cool and lubricate the bit, (2) transfer the cuttings from the bit face to the surface, (3) apply hydrostatic pressure to keep formation fluids fromentering the wellbore, and (4) maintain stability of the borehole. The drilling environment is changing to more hostile conditions because deeper and
4.0E+06 3.5E+06 3.0E+06 2.5E+06 2.0E+06 1.5E+06 1.0E+06 5.0E+05
drilling fluid total bentonite

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Figure 1: Bentonite total end use and use in drilling fluids in USA (fromUSGS, 2005).

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3rd International Conference on Sustainable Development Indicators in the Minerals Industry, June 2007, Milos island, Greece

more horizontal wells are drilled encountering, harder rock and abrasive formations, and higher pressures and temperatures. Drilling fluid research has resulted in a range of drilling fluids with many additives that are capable of performing theseformidable tasks in difficult environments. Among the properties that drilling fluid must posses are appropriate viscosity and fluid loss values. Additives together with bentonite are used to formulate drilling fluids for difficult drilling conditions. Bentonite, with montmorillonite as the principal component, when mixed with water forms non-Newtonian suspensions. Bentonite suspensions have the...