This paper presents high pressure PVT measurements and equation-of-state (EoS) modeling results for a GoM oil and for the oil mixed with nitrogen in various concentrations. The data includes:1. Upper and lower asphaltene onset pressures and bubble point pressures for the reservoir fluid swelled with nitrogen. At the reservoir conditions of 94 MPa (13,634 psia) and 94°C (201.2°F) asphaltene precipitation is seen after addition of 27 mole % of nitrogen. 2. Viscosity data for the swelled fluids showing that addition of nitrogen significantly reduces the oil viscosity. 3. Slim tube runs indicating that the minimum miscibility pressure of the oil with nitrogen is significantly higher than estimated from published correlations.The data has been modeled using the volume corrected Soave-Redlich-Kwong (SRK) and the Perturbed-Chain Statistical Association Fluid Theory (PC-SAFT) EoS. While both equations provide a good match of the PVT properties of the reservoir fluid, PC-SAFT is superior to the SRK EoS for simulating the upper asphaltene onset pressures and the liquid phase compressibility of the reservoir fluid swelled with nitrogen.Nitrogen gas flooding is expected to have a positive impact on oil recovery due to its favorable oil viscosity reduction and phase behavior effects.
Leif Hinderaker, SPE, Norwegian Petroleum Directorate, Rolf H. Utseth, SPE, Statoil, Odd Steve Hustad and Idar Akervoll, SPE, IKU Petroleum Research, Mariann Dalland, Bjorn Arne Kvanvik, Tor Austad, and John Eirik Paulsen, SPE, RF-Rogaland Research. Abstract RUTH (1992-1995) was a four year Norwegian research program on improved oil recovery funded by Norwegian authorities and 18 participating oil companies. This paper describes how the program was organized and highlights the main results. Research was performed within six main themes: Gas flooding, combined gas-water injection including WAG, foam, polymer-gels, surfactant flooding, and microbial method. Applications in Norwegian fields are discussed with special focus on field pilot tests. The program contributed to establish a pilot-activity on three new methods, WAG, foam, and polymer-gel, on the Norwegian continental shelf. Introduction An important goal for Norwegian petroleum policy has been to secure the best possible exploitation of the petroleum resources. The initiation and implementation of IOR R&D programs have been an essential part of the strategy to reach this goal. Several major Norwegian IOR programs have therefore been initiated since the nineteen eighties. These are listed on Table 1. The Joint Chalk Research program, dedicated to improving hydrocarbon production from Norwegian and Danish chalk fields, was launched in 1982 on the initiative of Norwegian and Danish authorities. The state sponsored SPOR program, which was carried out during 1985 through 1991, focused on IOR and EOR methods, and had as its main goal to build a national Norwegian IOR expertise. Two follow-up programs were initiated after SPOR: The PROFIT program, concentrating on "Reservoir Characterization" and "Near Well Flow", and RUTH. PROFIT was a collaborative program between 13 oil companies and the Norwegian Petroleum Directorate (NPD). About 50 million USD have been invested in these programs, including RUTH. RUTH (Reservoir Utilization through advanced Technological Help) was a cooperative IOR effort conducted by the Research Council of Norway, the Norwegian Petroleum Directorate, Norwegian research organizations, and 18 oil companies. The total program budget was 106 million NOK. The Research Council of Norway funded 55 million NOK, and 51 million NOK was funded by the participating oil companies (1 USD is about 6.50 NOK). The program lasted 4 years (1992-1995), and a total of 32 projects were performed. RUTH aimed at following tip the research topics included in the SPOR program which were not conducted by other programs, and to include new subjects of strategic importance. The main objectives were:–Contribute to increase oil recovery from sandstone and chalk reservoirs on the Norwegian continental shelf by 300 million Sm3.–Meet the authorities' specific and long-term requirements for research on advanced oil recovery.–Help Norwegian research groups to further develop an internationally recognized expertise that can be of use to the oil companies. Additional objectives were to concentrate on applied research that is related to advanced recovery methods and to help qualify advanced technology by means of field tests. Of the three main objectives, we believe the first objective will be reached through the use of the developed technologies, and that the other two objectives have been met. P. 251
A coupled formulation for three-phase capillary pressure and relative permeability for implicit compositional reservoir simulation is presented. The formulation incorporates primary, secondary and tertiary saturation functions. Hysteresis and miscibility are applied simultaneously to both capillary pressure and relative permeability. Two alternative three-phase capillary pressure formulations are presented, the first as described by Hustad (2002) and the second that incorporates six representative two-phase capillary pressures in a saturation weighting scheme. Consistency is ensured for all three two-phase boundary conditions, through the application of two-phase data and normalized saturations. Simulation examples of water alternating gas (WAG) injection are presented for water-wet and mixed-wet saturation functions. 1D homogeneous and 2D and 3D heterogeneous examples are employed to demonstrate some model features and performance.
This paper presents experimental and simulated results from two vertical core floods. The core floods consisted of injecting equilibrium gas and separator gas from the top of the core after water flooding from the bottom, respectively. The results show that an oil bank was formed in both experiments. When separator gas was injected, oil was also recovered by vaporization. Compositional analysis of the produced fluids during separator gas injection shows that considerable amounts of intermediate components were produced as condensate after gas breakthrough. Significant end effects were observed in the final water saturation profiles due to capillary hold-up. Analysis of the final oil saturation in the core indicates a significant gradient due to vaporization, and greater than that modeled by the compositional simulator based on an equation of state.
Saturation histories from simulations on a mesoscopic-scale heterogeneous model at immiscible and miscible conditions are compared with emphasis on gas segregation. Selected models for three-phase flow, and scaling of the end point saturations, relative permeabilities, and capillary pressures have been applied. The flow parameters of the facies were obtained from pore scale network modeling with input from North Sea sandstones. The simulation cases included water, gas, and water-alternating-gas (WAG) injection. Gas injection at irreducible water saturation demonstrates stronger gas segregation as the pressure exceeds the minimum miscibility pressure (MMP). Gas segregation is not so evident at the mesoscopic scale during WAG injection. High water saturation in the set-planes hampers the vertical gas flow. A bank of high oil saturation forms in front of the advancing gas at miscible conditions. Oil segregates to the set-plane below and the water cycle that follows mobilizes the accumulated oil. Introduction WAG and simultaneous water and gas (SWAG) injection have been successfully applied for several North Sea oil fields. 1–4 WAG has, in most cases, been implemented at a later stage of production as an improved recovery process after a long period of water injection. Both immiscible and miscible WAG injections have been applied. Increased recoveries by WAG have been attributed to improved sweep, reduction in residual oil saturation by gas flooding after a water flood, and compositional mass exchange between gas and oil such as swelling and vaporization. In a recent review article of reported worldwide field applications of WAG,5 the increased oil recovery was found to be in the range of 5 to 10% of the original oil in place. Recovery from attic oil or unswept oil of a dipping reservoir may be the most important target for WAG injection. Segregation of gas towards the top of the reservoir is expected to be a fast process in good quality reservoirs with high vertical permeability, high gas mobility, and strong gravity buoyancy for gas. However, low permeable heterogeneities with high capillary entry pressures will hamper immiscible gas to segregate. When approaching miscibility, such as in a multi-contact miscible process, the interfacial tension (IFT) between oil and gas becomes very small. The gas-oil capillary pressure is also reduced, and will vanish if miscible conditions are reached. Experiments have shown that there is an influence on relative permeability and residual saturations at low IFT values. 6 Tracking of the IFT at the gas front by correct fluid modeling is important close to miscibility. Immiscible WAG injection is associated with three-phase flow. WAG flooding under first contact miscible conditions is a two-phase flow situation where water and a single hydrocarbon phase are flowing. The transition from a three-phase gas, oil and water system to a two-phase hydrocarbon and water system must be modeled smoothly and continuously in the vicinity of miscibility. In this work we study gas segregation in a mesoscopic scale heterogeneous simulation model with low permeability layers (cross bedding) at immiscible and miscible conditions. Capillary forces, gravity forces and viscous forces are all expected to be important on this scale. The heterogeneous pattern is based on a North Sea reservoir formation. In ordinary reservoir simulations such heterogeneities are upscaled to a single homogeneous block. Relative permeabilities and capillary pressures of the individual rock types were estimated using a novel approach based on pore scale network modeling. 7,8
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.