WAG CO2 miscible injection project is planned to increase recovery from an oil r
ID: 2075874 • Letter: W
Question
WAG CO2 miscible injection project is planned to increase recovery from an oil reservoir. Following data are available:
ROS (residual oil saturation) = 40% Average porosity = 22%Initial reservoir pressure = 2600 psi Current reservoir pressure = 1500 psi MMP (CO2/oil system) = 1585 psi API gravity = 38 degree
CO2 density is about 1.5 times that of air (assume same in reservoir condition) Formation thickness = 120 feetFormation width = 200 feetFormation is tilted making a dipping angle = 25 degrees
Oil viscosity = 1.2 cpKo = 16 mdKCO2 = 75 mdIFT for oil/CO2 system = 2 mN/m
Mobility ratio=380.068
Capillary number=102.326
Critical velocity for stable displacement=44762 ft/s
Injection flow rate per well to reach critical velocity= 2.238 x 1011 ft3/s
Can you help planning the project by determining the following decisive parameters?
a) Would it be a better idea to consider N2 instead of CO2? Knowing that: N2 can be extracted from air with trivial cost.MMP (N2/oil system) = 2500 psiCO2 density is 1.8 times that of air (assume same in reservoir condition) KN2 = 75 mdIFT for oil/N2 system = 2.5 mN/m
b) Tabulate a comparison between CO2 and N2 miscible injections for this reservoir with advantages and disadvantages of each of the solvents
- Make good assumptions if necessary
Explanation / Answer
EOR gas flooding has been the most widely used recovery methods of light, condensate and volatile oil reservoirs. Although nitrogen (N2) injection has been proposed to increase oil recoveries under miscible conditions favoring the vaporization of light fractions of light oils and condensates, today few N2 floods are ongoing in sandstone reservoirs. Immiscible N2 floods are reported in Hawkins Field (Texas) and Elk Hills (California) based on the Moritis EOR survey in 2008. No new N2 floods in Energies 2010, 3 1538 sandstone reservoirs have been documented in the literature during the last few years and we do not foresee an increment in the number of projects implementing this EOR gas flooding method. Similarly to N2 injection, hydrocarbon gas injection projects in onshore sandstone reservoirs have made a relatively marginal contribution in terms of total oil recovered in Canada and the U.S. other than on the North Slope of Alaska, where large natural gas resources are available for use that do not have a transportation system to markets. It is important to mention that in this paper we refer to EOR gas methods using hydrocarbon gases such as Water-Alternating-Gas (WAG) injection schemes, enriched gases or solvents and its combinations. Therefore, hydrocarbon gas injection as pressure maintenance or double displacement strategies are not considered EOR methods for purposes of this review. Most of immiscible and miscible EOR hydrocarbon gas floods in the U.S. are on the North Slope of Alaska while in Canada a miscible gas flood is reported in Brassey Field. The situation of hydrocarbon gas injection projects is different in offshore sandstone reservoirs. In general, if there is no other way to monetize natural gas, then a more practical use of natural gas would be to use it in pressure maintenance projects or in WAG processes. However and if available, the substitution of hydrocarbon gases by non-hydrocarbon gases (N2, CO2, acid gas, air) oil recovery will make more natural gas available for domestic use or export while still maintaining reservoir pressure and increasing oil recoveries. Despite current low natural gas prices, the continued increase in energy demand will likely affect the viability of new large-scale hydrocarbon gas projects. On the other hand, CO2 flooding has been the most widely used EOR recovery method for medium and light oil production in sandstone reservoirs during last decades, especially in the U.S. due to the availability of cheap and readily available CO2 from natural sources. The increasing trend in the number of CO2 field projects in the U.S during the last decade in both, sandstone and carbonate reservoirs. The number of CO2 floods is expected to continue to grow in U.S. sandstone reservoirs. Some examples of planned CO2-EOR projects in the U.S. include Cranfield Field, Heidelberg West (from anthropogenic sources) and Lazy Creek Field in Mississippi and Sussex Field in Wyoming. Number of CO2 floods in Wyoming sandstone reservoirs are also expected to increase based in a recent evaluation presented (this will be constrained by availability of CO2 for injection). Additionally, Holtz recently reported an overview of sandstone gulf coast and Louisiana CO2-EOR projects to estimate EOR reserve growth potential in the area including sandstone reservoirs in the Gulf of Mexico. CO2-EOR in the U.S. has shown a vast potential to increase oil recovery and has been widely documented in the literature. Therefore, the present review will address briefly activities reported outside the U.S. Some examples of CO2-EOR field projects in sandstone formations presented in various conferences and/or documented in the literature are summarized below: Brazil reports CO2 floods in Buracica and Rio Pojuca fields and announced a CO2 flood in Miranga Field from anthropogenic sources as an EOR and carbon storage strategy . Canada actually reports CO2 floods in Joffre and Pembina fields. Operators and government institutions of Canada have been very active evaluating CO2-EOR potential during the last decade. Recently PTAC (Petroleum Technology Alliance of Canada) Energies 2010, 3 1539 estimated an up-side potential of CO2-EOR in Alberta of 3.6 billion barrels over the next two decades at oil prices of $45/bbl. Croatia reported a CO2 pilot injection at Ivani Field injecting CO2 transported by trucks. Pilot results (2001–2006) contributed to define larger application of CO2-EOR in the country considering the use of CO2 from anthropogenic sources . Hungary also reports more than four decades experience in CO2-EOR floods. CO2 projects at Budafa and Lovvaszi fields are two cases well documented in the literature . Szank Field represents a more recent CO2-EOR flood in Hungary using CO2 from a sweetening plant. Trinidad also has more than three decades experience operating CO2-EOR projects using CO2 an ammonia plant nearby the fields. Moritis EOR survey reports up to nine (9) active immiscible CO2 floods operating since mid 1970s. As can be seen, CO2-EOR has become one of the preferred EOR processes globally and considering CO2 from natural and industrial sources. Mexico and the U.S. are just few examples of countries evaluating CO2 sources and EOR potential in mature fields and mature CO2 floods . However, this will be further discusses in the section of EOR gas methods in carbonate formations.
Hydrocarbon gas injection (continuous or in a WAG mode) continues to be the preferred recovery process in offshore fields, gas condensate reservoirs, or fields in remote locations without access to gas markets. N2 EOR projects seem to be in decline except in the Campeche Bay Area in Mexico because of the availability of vast installed N2 generation capacity. CO2 injection is getting most of the attraction as an EOR method and potentially as a sequestration strategy in recent years. However, CO2-EOR projects in operation are mostly concentrated in the U.S. (especially in the Permian Basin) and associated to natural sources of CO2. CO2-EOR/sequestration projects are not expected to grow in the near future until industrial sources of CO2 are produced at much lower costs and the proper regulatory framework is in place.
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