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The search for the optimal development of a field involves proper knowledge of the composition of the fluids that impregnated the reservoirs. The development scheme could be strongly affected by the connectivity between the different reservoir units. After their migration into the trap, the fluids are shaped by various forces, among them, gravity has the most striking effect and was widely studied. In many cases there is evidence for the contribution of other forces like thermal gradients. Taking into account all the phenomena, to establish a consistent picture of fluids distribution in the field is an important challenge for the petroleum industry. Reciprocally the actual fluid distribution can be used to assess the connectivity of the different panels and layers. In that case, all the possible compositional redistribution mechanisms have to be taken into account. In some circumstances, particularly in recent mature and permeable petroleum systems, hydrocarbon accumulations are subjected to gas fluxes, which lead to non-conventional fluid distribution. There are already a number of tools available for calculating the compositional gradient within a reservoir, including the contribution of gravity and thermal gradient. In many field cases, however, the calculated profile differs from actual. The discrepancies are input to another external force: the mass flux of light component at the reservoir boundaries. In this paper, the authors present the modeling of diffusion fluxes across the reservoir and point out how the diffusion fluxes can reveal the permeability barriers through the pressure and the compositional profiles. Drawing on a field example, this paper provides a methodology for dealing with dynamic reservoir fluid systems. The model matches the observed compositional gradient and corresponding PVT properties. It allows reliable connectivity assessment in cases where gravitational modeling fails. Introduction The PVT properties of the various samples taken from a reservoir may be very different. Although accurate knowledge of each sample is necessary, this does not usually extend in obvious fashion to the reservoir as a whole. Therefore, reservoir fluid evaluation is compulsory as a preliminary study before any development plan and it must be updated regularly during the life of the field. All the fluid data are required to reach a comprehensive knowledge of the fluid system and many complementary reservoir data as pressure, temperature and logs are essential. Gravity segregation models allow us to calculate the composition of the fluid at any depth in the reservoir fluid column from the composition at a reference depth, just by adding the gravity contribution to the chemical potential of the components[1–4]. This option is now included in most of the PVT software's. Unfortunately in many field cases, the actual compositional profile cannot be obtained with this single external force. The capillary forces can lead to significant differences in the case of two-phase reservoirs[5–6] and the thermal field is obviously responsible for part of the discrepancies[7–12] but the most striking difference certainly comes from the dynamic situation of the reservoirs[13–17].

Full scale gas kick experiments have been performed. The objectives of the experiments were to gain more knowledge during the circulation out of gas kicks in a horizontal well through the study of the behaviour of the two-phase flow at high pressures. The horizontal wellbore was simulated on the surface by a 200 m long flow loop (casing) with an inside diameter of 9 1/4". The inside of the well had a drillstring with a 50 m long drill collar section. The drillstring assembly could be rotated. Also, the last 50 m of the well near the bit was inclined upward with 4 from horizontal for part of the experiments. The wellbore was designed for pressures up to 170 bars. The gas used during tests was air. Two different liquids; water and CMC polymer solution, were tested. During the experiments the main parameters varied were mud circulation rates, gas injection rates, system pressure and drillstring rotation. Three test categories were performed. During DISPERSION tests, single bubbles of gas were injected and circulated out in order to study the gas dispersion along the horizontal well. During FLOW TESTS, a continuos injection of gas was performed to study gas velocity, flow regime and pressure loss. During CLEAN-OUT TESTS, methods for circulating out stationary gas positioned in traps in the well were studied. New correlations for gas transport velocities and frictional pressure losses have been developed based on these data as well as data from two low pressure flow loop tests. Results from the full scale tests as well as the new correlations are presented in this paper. Introduction Gas kicks may develop into major well control incidents. A gas kick situation in a horizontal well may for the future occur more frequently than today. The industry is moving towards fewer appraisal wells and early production. This may lead to pressure surprises. Also horizontal well drilling in reservoirs with water or gas injection or in depleted reservoirs may lead to surprises related to pressure. Studies related to kick development and control have been performed. These include full scale experiments, development of kick simulators and the related gas rise velocity models. Studies on kick control in horizontal wells have been few. These include computer simulations, well control evaluations and experimental studies. The results from the experimental studies have been implemented into a horizontal kick simulator. These experiments were performed at low pressures. and in a 12 m long model loop. It is important to study gas kick development and control in horizontal wells, for two reasons mainly. First, development of general procedures and guidelines for well control of horizontal wells are needed, procedures like minimum mud velocities for gas clean out in a given mud/well; or procedures to clean out gas when minimum clean out velocity is unobtainable etc. Secondly, further development of models related to gas kick development and control in horizontal wells are needed. Such models will be important parts of and inputs to the development of advanced kick simulators for horizontal wells. Horizontal wells vary tremendously related to angle, build-up, length, detailed profile and existence of gas traps in the well. In order to develop well specific well control plans and procedures. simulations with an advanced kick simulator for horizontal wells is necessary. The most important models are those for gas transport velocities, frictional pressure losses and removal rate by gas dissolution. Gas transport velocities are significantly higher for annuli than for pipe flow. P. 765

Summary Hybrid steam-solvent processes have gained importance as a thermal-recovery process for heavy oils in recent years. Numerous pilot projects during the last decade indicate the increasing interest in this technology. The steam/solvent coinjection process aims to accelerate oil production, increase ultimate oil recovery, reduce energy and water-disposal requirements, and diminish the volume of emitted greenhouse gases compared with the steam-assisted-gravity-drainage (SAGD) process. Among the identified physical mechanisms that play a role during the hybrid steam/solvent processes are the heat-transfer phenomena, the gravity drainage and viscous flow, the solvent mass transfer, and the mass diffusion/dispersion phenomena. The major consequence of this complex interplay is the improvement of oil-phase mobility that is controlled by the reduction in the oil-phase viscosity at the edge of the steam chamber. It follows that a detailed representation of this narrow zone is necessary to capture the involved physical phenomena. In this work, a study of sensitivity to grid size was carried out to define the appropriate grid necessary to represent the near-edge zone of the steam/solvent chamber. Our results for the steam/solvent coinjection process in a homogeneous synthetic reservoir indicate that a decimetric scale is required to represent with a good precision the heat and mass-transfer processes taking place at the edge of the steam chamber. In addition, we present some numerical results of the adaptive dynamic gridding application. Comparison was performed between the SAGD process and steam/solvent coinjection after the characterization and analysis of the mechanisms that govern oil production under typical Athabasca oil-sand conditions. Finally, in the framework of the proposed numerical methodology, the effect of solvent type and injection conditions on the oil-recovery efficiency is quantitatively illustrated. Published data for similar applications are also discussed. It is expected that this work will provide some insight for the simulation community about methodological aspects to be taken into account when hybrid steam/solvent processes would be modeled.