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Collaborating Authors
Drilling fluid management & disposal
Abstract Terra Nova oil pool is the second largest oil pool discovered in the Grand Banks of the Canadian East Coast and is under development with production startup target date in late 2000. As a part of the oil recovery process selection criteria, miscibility conditions were determined for Terra Nova oil with various enrichment levels of gas available from the offshore production facilities, using the newly developed Vanishing Interfacial Tension (VIT) technique. The VIT technique is based on the concept that the interfacial tension between the gas and crude oil phases at reservoir temperature must reduce to zero as these two phases approach the point of miscibility. The concept of zero-interfacial tension at miscibility is, in turn, based on the well-accepted fact that the interface between the phases must vanish, as they become miscible with one another. Thus, the minimum miscibility pressure (MMP) and minimum miscibility composition (MMC) can be determined precisely by measuring gas-oil interfacial tension as a function of pressure and gas composition, down to as low an interfacial tension as the measurement technique allows, and then extrapolating the data to zero interfacial tension. This paper presents the details of this new VIT technique and its evaluation against slim-tube tests, and discusses its application to the Terra Nova gas injection scheme. The interfacial tension data obtained at reservoir conditions using the computerized axi-symmetric drop shape analysis technique are presented as a function of pressure, gas composition, and the mode of gas-oil contact (first contact or equilibrium). In addition to providing visual evidence of miscibility as the point of zero interfacial tension is approached, the VIT technique is rapid in that it enables the experimental determination of MMP and MMC within about 2โ3 days as against 4โ6 weeks required by the slim-tube technique. Introduction Nearly two-thirds of the original oil in place is left behind in reservoirs at the end of primary recovery and secondary waterfloods. This amounts to a staggering 351 billion barrels of unrecovered, known-to-exist oil in the US alone and two trillion barrels of oil in the world (Green and Willhite, 1998). Gas injection EOR projects account for about 40% of EOR production in the US, with the remaining 60% of EOR production coming from steam injection projects (Moritis, 1998). For gas injection projects to be successful economically, they need to be operated at or near the conditions required for miscibility between reservoir crude oil and injected gas. Hence the need to asses gas/oil miscibility pressures and compositions at the operating temperature. The following are some definitions of miscibility appearing in the literature. Miscible displacement is a process where there is an absence of phase boundary or interface between the displaced and displaing fluids (Benham et. al., 1965). Two fluids are miscible when all mixtures of these two fluids in all proportions remain in a single phase without any interfaces, and consequently with no interfacial tension, between the fluids (Stalkup, 1983). Miscibility is that physical condition between two or more fluids which permits them to mix in all proportions without the existence of an interface (Holm, 1987). Two fluids that mix together in all proportions within a single fluid phase are miscible (Lake, 1989).
- North America > United States (1.00)
- North America > Canada > Newfoundland and Labrador > Newfoundland (0.28)
- Well Drilling > Drilling Fluids and Materials > Drilling fluid management & disposal (1.00)
- Reservoir Description and Dynamics > Improved and Enhanced Recovery > Miscible methods (1.00)
- Reservoir Description and Dynamics > Improved and Enhanced Recovery > Gas-injection methods (1.00)
Interface Light Scattering Measurement of Low Interfacial Tension on a Gas Condensate System at High Pressure and Temperature
Lindeberg, E.G.B. (IKU Petroleum Research) | Bjorkvik, B.J.A. (NTNU The Norwegian University of Science and Technology) | Strand, K.A. (NTNU The Norwegian University of Science and Technology)
Abstract A laser light scattering technique was used to measure simultaneously accurate values for the interfacial tension (IFT) and the sum of gas and liquid viscosities in a low IFT (< 1 mN/m) real gas condensate system at high pressure (30-41 MPa) and high temperature (124 C) reservoir conditions. The measured IFT values were found to be three to five times as large as estimated values obtained by a pVT simulator using compositional data and the Weinaug-Katz correlation. thus demonstrating the need of good experimental IFT data on low IFT gas condensate systems. Introduction Accurate measurement of low interfacial tension (IFT) (<1 mN/m) in oil/gas systems at high pressure and temperature reservoir conditions represents a considerable experimental challenge. Two techniques have proved successful for accurate IFT measurement under these conditions. i.e. the optical technique of interface laser-light scattering (ILLS) spectroscopy and the drop shape technique using pendant drops. Of the two the ILLS method is the one best suited for the low IFT range. partly because the laser beam represents a non-contact and low-perturbative probe, partly because the signal strength increases with decreasing IFT. Whereas the pendant drop technique has been used for accurate measurement of oil/gas IFT down to approximately 5.10-2 mN/m, the ILLS method has been used down to 10-3 mN/m, and has the capability of reaching even lower values (<10-4 mN/m), as shown in measurements on microemulsion systems. (The only alternative technique in this IFT range, the drop shape technique using spinning drops, is not as convenient at elevated pressures and temperatures.) The present paper demonstrates accurate ILLS measurement of low IFT on a real light brown gas condensate system (composition in Table 1) at high pressure (30-41 MPa) and high temperature (124 C) reservoir conditions. The ILLS instrument has been described in detail elsewhere, excepting the optical high-pressure cell, which was specially designed and constructed for the present work. (The high-pressure cell used previously for IFT measurement on a synthetic transparent gas condensate system, had not sufficient strength for the present pressure and temperature conditions). The main difficulty of applying the ILLS method to real reservoir fluids is that such fluids in greater or less degree absorb light. When a laser beam of sufficient intensity is incident upon the surface of a photoabsorbing liquid. the laser can cause surface heating. This generally results in surface deformation and defocusing of the laser beam, which is seriously detrimental to ILLS measurement. A prime requirement for the successful ILLS measurement on a photoabsorbing system is therefore that the incident laser intensity be kept low. This low intensity constraint has hitherto restricted ILLS measurement on photoabsorbing fluids to very small scattering angles (0.1). (The reason is that the intensity of light scattered at a fluid interface is very weak and diminishes rapidly in strength with increasing scattering angle.) The main disadvantage of working at such small scattering angles is that the experimental data have to be corrected for effects of instrumental resolution. P. 265
- Energy > Oil & Gas > Upstream (1.00)
- Materials > Chemicals > Commodity Chemicals > Petrochemicals (0.46)
- Reservoir Description and Dynamics > Unconventional and Complex Reservoirs > Gas-condensate reservoirs (1.00)
- Reservoir Description and Dynamics > Improved and Enhanced Recovery (1.00)
- Reservoir Description and Dynamics > Fluid Characterization (1.00)
- Well Drilling > Drilling Fluids and Materials > Drilling fluid management & disposal (0.90)