In this experimental work the rheological behavior of umbu pulp has been studied by shear flow (pseudoplasticity, apparent viscosity) and in oscillatory mode (dynamic modules) in the linear domain of viscoelasticity. The studies were carried out with the use of a controlled stress Rheometer Haake RS 100, at different soluble solid concentrations (10, 15, 20 and 25 °Brix), measured at 30 °C. Tests in steady shear were conducted over a shear rate range of 0.1 - 300 s-1 and oscillatory measurements over a frequency range of 0.01 - 100 Hz. The results indicated that umbu pulp behaves as a non-Newtonian fluid, with pseudoplastic characteristics and yield stress appearance and exhibits tixotropic properties. Rheograms were fitted to the Herschel-Bulkey model. From the dynamic test the umbu pulp showed storage modulus (G') values that were always higher than loss modulus (G"), indicating weak gel-like behavior. Storage and loss modulus increased with increase in the concentration.

RESUMO: Duas amostras de pectina de alto grau de metoxilação, amostras A e B, foram purificadas, levando-se em conta os teores em grupos metoxílicos. Sua caracterização estrutural foi realizada através de dosagem de açúcares neutros com auxílio de cromatografia gasosa, GLC, e determinação do grau de metoxilação por técnicas de cromatografia líquida de alta resolução, HPLC. A amostra A apresentou teores mais elevados em açúcares neutros totais e grau de metoxilação mais alto. As viscosidades intrínsecas, [eta] = 3,68 dL/g e [eta] = 3,56 dL/g foram determinadas a pH 7,0 para as amostras A e B, respectivamente. A pH 3,0, valores menores foram obtidos. A gelificação das amostras foi investigada, em função da concentração e da temperatura, medindo-se os módulos de armazenamento, G', e de perda, G", em função do tempo. A pH 3,0 a pectina A apresentou taxas de gelificação mais elevadas, tanto em função da concentração como da temperatura.

No abstract

Nowadays, it is commonplace to say that acid fracture conductivity depends on the fracture face asperities. Does it really depend on it? Almost thirty years ago, someone wrote, "We believe the conductivity measured in these tests is mainly due to the smoothing of peaks and valleys on the rough fracture faces, and is independent of rock heterogeneities due to the small sample size." Moreover, almost one year ago, one wrote, "More asperities touch and deform as the closure stress increases. The channels become even shorter and fewer openings are left." Between these two extremes, the asperities came to be pointed out as an essential factor to generate acid conductivity. Many published results from small, wet sawed and leveled carbonate rock samples support such claim. We did the same. Our experimental investigation on small scale carbonate samples with sawn faces, both from outcrops and well cores, reconfirm the existence of three main acid patterns namely uniform, channels and roughness. The design of experimental apparatus prevented that those etching patterns were artifact patterns. The acid etching patterns determine different conductivity behavior under confining stress. However, hydraulic fractures are tensile fractures and they are naturally rough. In nature, there is no such thing as a leveled fracture face. Tensile fracture faces could be rougher than fracture face after acid reaction. In fact, the first experimental results show that after acid reaction, linear roughness of tensile fractures can be larger, equal or less than linear roughness before acid reaction. This paper presents experimental results and discusses the asperities paradigm.

Fluid invasion into productive zones has been widely recognized as detrimental to well productivity. Filtrate and solids invasion can cause irreversible formation damage and permeability reduction. Drilling fluids are formulated to avoid excessive fluid penetration into productive zones. Non-damaging acid-soluble solids are usually added to drill-in fluids in order to promote pore plugging and minimize fluid penetration. Also specific polymers are used that reduce fluid invasion due to surface chemistry and viscosity effects. The development of less invasive non-damaging fluid formulations requires the knowledge of filtration mechanisms of solids containing polymeric solutions in porous media. The work was carried out in two ways: solids with different particle size distributions and concentrations were added to a polymeric base formulation and the filtration behavior of the fluids through unconsolidated porous media was evaluated using computer tomography scanning. Along with the solids investigation, different types of polymeric solutions exhibiting different shear and extensional rheological properties were tested using the same procedure and technique. The extent of the invaded zone could then be measured and the performance of the different types of material could be evaluated. The results from the lab tests will be used to support the development of a filtration model to calculate filtration flow rates and depth of penetration accounting for non-newtonian rheology and type of bridging agent on filtration mechanism. Introduction To better understand the relative importance of factors contributing to filtration, an extensive experimental work is required to support the development of a mathematical model to predict filtration rates and depth of penetration. The paper presents a methodology to evaluate filtration properties of drilling fluids through unconsolidated porous media. Results from static filtration experiments of polymeric fluid formulations are presented aiming: the development of a filtration model to calculate filtration flow rates and depth of penetration accounting for non-newtonian rheology and type of bridging agent on filtration mechanism; the evaluation of filtration characteristics of different fluid formulations; the effect of different polymers and bridging agents on filtration properties of fluids; the development of non-invasive fluid formulations. Background Theoretical and experimental studies on static and dynamic filtration of water based drilling fluids have been carried out to evaluate the effects of fluid type and pH, solids shape, size and concentration, pressure and shear rates on filtration properties of the fluids1. The inadequate control of fluid properties is usually associated with wellbore instability, excessive torque and drag, differential stuck pipe and formation damage2. Therefore, it is imperative to correctly estimate the filtration characteristics of the fluids during drilling and completion so as to properly diagnose and prevent the above-mentioned problems. Moreover, severe fluid losses experienced during drilling in ultra deep waters have brought the attention to the need for non-invasive fluids to guarantee a successful operation. One of the main problems related to the presence of filtrate in productive oil and gas zones is the significant permeability reduction and well productivity decrease. The modeling of filtration process as to predict permeability changes and depth of damage penetration into the productive zone is essential to establish the stimulation technique that will better remove the existing damage3.