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International audienceExperiments on vertical turbulent flow with millimetric bubbles, under three gravity conditions, upward, downward and microgravity flows (1g, -1g and 0g), have been performed to understand the influence of gravity upon the flow structure and the phase distribution. The mean and fluctuating phase velocities, shear stress, turbulence production, gas fraction and bubble size have been measured or determined. The results for 0g flow obtained during parabolic flights are taken as reference for buoyant 1g and -1g flows. Three buoyancy numbers are introduced to understand and quantify the effects of gravity with respect to friction. We show that the kinematic structure of the liquid is similar to single-phase flow for 0g flow whereas it deviates in 1g and -1g buoyant flows. The present results confirm the existence of a two-layer structure for buoyant flows with a nearly homogeneous core and a wall layer similar to the single-phase inertial layer whose thickness seems to result from a friction-gravity balance. The distributions of phase velocity, shear stress and turbulence are discussed in the light of various existing physical models. This leads to a dimensionless correlation that quantifies the wall shear stress increase due to buoyancy. The turbulent dispersion, the lift and the nonlinear effects of added mass are taken into account in a simplified model for the phase distribution. Its analytical solution gives a qualitative description of the gas fraction distribution in the wall layer

Summary In-Situ Combustion. In-situ combustion (ISC) is an enhanced oil-recovery method. Enhanced oil recovery is broadly described as a group of techniques used to extract crude oil from the subsurface by the injection of substances not originally present in the reservoir with or without the introduction of extraneous energy (Lake 1996). During ISC, a combustion front is propagated through the reservoir by injected air. The heat generated results in higher temperatures leading to a reduction in oil viscosity and an increase of oil mobility. There are two types of ISC processes, dry and wet combustion. In the dry-combustion process, a large part of the heat generated is left unused downstream of the combustion front in the burned-out region. During the wet-injection process, water is co-injected with the air to recover some of the heat remaining behind the combustion zone. ISC is a very complex process. From a physical point of view, it is a problem coupling transport in porous media, chemistry, and thermodynamics. It has been studied for several decades, and the technique has been applied in the field since the 1950s. The complexity was not well understood earlier by ISC operators. This resulted in a high rate of project failures in the 1960s, and contributed to the misconception that ISC is a problem-prone process with low probability of success. However, ISC is an attractive oil-recovery process and capable of recovering a high percentage of oil-in-place, if the process is designed correctly and implemented in the right type of reservoir (Sarathi 1999). This paper investigates the effect of water on the reaction kinetics of a heavy oil by way of ramped temperature oxidation under various conditions. Reactions. Earlier studies about reaction kinetic were conducted by Bousaid and Ramey (1968), Weijdema (1968), Dabbous and Fulton (1974), and Thomas et al. (1979). In these experiments, temperature of a sample of crude oil and solid matrix was increased over time or kept constant. The produced gas was analyzed to determine the concentrations of outlet gases, such as carbon dioxide, carbon monoxide, and oxygen. This kind of studies shows two types of oxidation reactions, the Low-Temperature Oxidation (LTO) and the High-Temperature Oxidation (HTO) (Burger and Sahuquet 1973; Fassihi et al. 1984a; Mamora et al. 1993). In 1984, Fassihi et al. (1984b) presented an analytical method to obtain kinetics parameters. His method requires several assumptions.

Underbalanced drilling (UBD) holds several important advantages over conventional drilling technology. These include minimization of formation damage, faster penetration rate, and ability for evaluation of reservoir productivity during the drilling process. As UBD technology matures, it has also been used more and more in different applications. However, many aspects of UBD technology remain poorly understood. The model presented in this paper seeks to understand the mechanisms involved in the transport of cuttings in UBD.The model simulates the transport of drill cuttings in an annulus of arbitrary eccentricity and includes a wide range of transport phenomena, including cuttings deposition and resuspension, formation, and movement of cuttings bed. The model consists of conservation equations for the fluid and cuttings components in the suspension and the cuttings deposit bed. Interaction between the suspension and the cuttings deposit bed, and between the fluid and cuttings components in the suspension, are incorporated. Solution of the model determines the distribution of fluid and cuttings concentration, velocity, fluid pressure, and velocity profile of cuttings deposit bed at different times.The model is used to determine the critical transport velocity for different hydrodynamic conditions. Results from the model agree quite closely, qualitatively, with experimental data obtained from a cuttings transport flow loop at the Technology Research Center of the Japan Natl. Oil Corp. (TRC/JNOC)'s Kashiwazaki Test Field in Japan. These results show the importance of slippage in the formation of the cuttings deposit bed. The model is useful in evaluating the minimum flow rate for effective cuttings removal in UBD.

TX 75083-3836, U.S.A., fax 01-972-952-9435. AbstractA review is presented on the state-of-the-art of mechanistic cuttings transport modeling. Cuttings transport predictions are essential for the planning of directional and horizontal drilling. It is suggested that field requirements (the need for fast, easy to use, simulators) point towards the use of a combination of two distinct modeling strategies, which are layer-models for the flow along the wellbore, and full numerical solutions in given cross-sectional areas. The layer model approach is developed in detail, yielding a two-layer model that simulates a moving bed of packed cuttings below a heterogeneous layer of mud and cuttings. Some key points on which more research is needed are highlighted.The model has been used to perform numerical simulations, predicting cuttings bed heights, pressure drops, and transport velocities at different rate of penetrations and mudflow rates. Results have been compared to predictions by correlation-based models. The observed differences are discussed and improvements on the current model are proposed.