Rosana Fatima Teixeira Lomba

Concentration Regimes of Biopolymers Xanthan, Tara, and Clairana, Comparing Dynamic Light Scattering and Distribution of Relaxation Time

The aim of this work was to evaluate the utilization of analysis of the distribution of relaxation time (DRT) using a dynamic light back-scattering technique as alternative method for the determination of the concentration regimes in aqueous solutions of biopolymers (xanthan, clairana and tara gums) by an analysis of the overlap (c*) and aggregation (c**) concentrations. The diffusion coefficients were obtained over a range of concentrations for each biopolymer using two methods. The first method analysed the behaviour of the diffusion coefficient as a function of the concentration of the gum solution. This method is based on the analysis of the diffusion coefficient versus the concentration curve. Using the slope of the curves, it was possible to determine the c* and c** for xanthan and tara gum. However, it was not possible to determine the concentration regimes for clairana using this method. The second method was based on an analysis of the DRTs, which showed different numbers of relaxation modes. It was observed that the concentrations at which the number of modes changed corresponded to the c* and c**. Thus, the DRT technique provided an alternative method for the determination of the critical concentrations of biopolymers.

Comportamento reológico de xantana produzida por Xanthomonas arboricola pv pruni para aplicação em fluido de perfuração de poços de petróleo

The aim of this work was to evaluate xanthans produced by Xanthomonas arboricola pv pruni to be used for increasing the viscosity of fluids applied in the perforation of oil wells, which were compared with three commercial samples. In order to do that, the viscosity of aqueous and saline solutions (NaCl, KCl and CaCl2) from different xanthans, at different temperatures (25, 45, 65 and 80 oC), was determined in a rheometer. The rheological parameters consistency index (K) and flow behaviour index (n) were obtained by adjusting the data with the Ostwald-de-Waelle model. Gel strength (G0, G10 e G30) was determined in a viscometer, and the concentration of monovalent (sodium and potassium) and divalent salts (calcium and magnesium) was determined in flame photometer and in atomic absorption spectrometer, respectively. Taken together, the results obtained in this study showed that xanthans produced by patovar pruni, Xp 106-600 and Xp 115-600, are promising for fluids used in oil well perforation with saline solutions, because they have low concentration of salts. As for the commercial polymers, they presented the best results when used in aqueous solution, because they had high salt concentrations.

A New Approach to Evaluate Temperature Effects on Rheological Behavior of Formate-Based Fluids

Organic salt brines represent a good alternative to drill through deep productive zones. The literature presents these salts as thermal stabilizers of polymers used in the formulation of drill-in fluids. An extensive study was carried out to evaluate the rheological behavior of formate-based fluids as a function of temperature and density. An analytical expression was developed to correlate shear stresses with temperature for general drilling fluids and a special case of this expression results in a greatly simplified expression that is valid for a number of drilling and completion fluids produced using different alkalimetal salts of formic acid. The advantage of this new approach is the lack of dependence between the proposed correlation and the choice of a rheological model. Unlike many expressions presented in the literature, the expression proposed and methodology that follows allows the choice of a best-fit model to predict the fluids rheological behavior as a function of temperature. Experimental results show that formates do improve the thermal stability of polymers. The proposed correlations will soon be incorporated in a wellbore cleaning numerical simulator to compensate for thermal effects.

AVALIAÇÃO DO POTENCIAL USO DE BIOGLICERINA COMO BASE PARA FORMULAÇÃO DE FLUIDOS DE PERFURAÇÃO AQUOSOS PARA POÇOS DE PETRÓLEO E GÁS

Cleysson C. Corrêaa, Georgiana F. da Cruza,*, Alexandre S. L. Vaz Jra, Bianca de S. A. Araújoa, Alexsandro A. da Silvab, Rafael A. Rodriguesb , Rosana F. T. Lombac e Alex T. de A. Waldmannc Laboraório de Engenharia e Exploração de Petróleo, Universidade Estadual do Norte Fluminense Darcy Ribeiro, 27.925-535 Macaé – RJ, Brasil Central Analítica Fernanda Coutinho, Instituto de Química, Universidade do Estado do Rio de Janeiro, 20550-900 Rio de Janeiro – RJ, Brasil Centro de Pesquisas e Desenvolvimento Leopoldo Américo Miguez de Mello, Cidade Universitária, 21941-915 Rio de Janeiro – RJ, Brasil

Full-Scale Laboratory Study of the Impact of Drilling Fluid Composition and Properties on Penetration Rates in Brazilian Pre-Salt Carbonates

Massive hydrocarbon reserves exist in the pre-salt carbonate formations in deepwater offshore Brazil. Very low penetration rates, around 2 m/hr, and very high rig costs provide a strong incentive to improve drilling performance here. The work for this paper forms part of a project combining application engineering and laboratory studies to meet this objective. Full-scale laboratory drilling tests were used to benchmark the drilling performance of the drilling system preferred at the start of the project and to investigate the performance potential of new bit designs and different drilling fluids. This paper describes the drilling fluid tests, presents and analyses their results, and draws conclusions on drilling fluid formulation for high penetration rate performance in pre-salt carbonates.