该文选自SPE
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【Paper Number 】 IPTC-11234-MS
【Title】 Review of and Outlook for Enhanced Oil Recovery Techniques in Kuwait Oil Reservoirs
【Authors 】Saad F. Alkafeef, SPE, and Alforgi M. Zaid, SPE, College of Technological Studies
Source International Petroleum Technology Conference, 4-6 December 2007, Dubai, U.A.E.
【Copyright 】2007. International Petroleum Technology Conference------------------------------------------------------------------------
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Enhanced Oil Recovery Screening Criteria【第一段】
Before applying enhanced oil recovery to any reservoir, a screening study is the first thing to be considered. The study normally consists of a complete study of oil properties and reservoir characteristics. There were three comprehensive studies conducted in the 1970s on enhanced oil recovery. These were the 1976 studies by the National Petroleum Council(NPC) and Lewin and Associates, prepared for the U.S. Federal Energy Administration, and the 1978 study for the Office of Technology Assessment(OTA).
【第二段】
In addition, most of the oil companies have their own technical screening for enhanced oil recovery. After technical screening criteria have been met, other items that will be taken into consideration are cost of the project, laboratory work, and a computer simulation to predict the amount of oil recovery. When a field has more than one reservoir, each reservoir should be evaluated individually by a screening guide, and a complete study of the reservoir should be performed. A geological study should be considered, since geological factors may cause the EOR process to fail because of unexpected reservoir problems.
【第三段】
Enhanced oil recovery mechanisms are divided into three basic mechanisms: reduction or elimination of the interfacial tension between oil and displacing fluid(s),oil viscosity reduction, and macroscopic sweep efficiency improvement. The purpose of the screening criteria analysis is to investigate the applicability of one or more such mechanisms to the reservoir in question. Table(1)shows screening criteria used to select the appropriate enhanced oil recovery methods.3-5 The EOR methods considered are gas injection, chemical flooding, and thermal recovery.
【第四段】
The main factor to be considered in miscible flood is the average pressure necessary to achieve miscibility in the system, which is depth dependent. A minimum depth of 2000 ft for LPG and 5000 ft for high pressure gas drive is suggested. The API gravity should be more than 35o and oil viscosity less than 3 cp. The nitrogen and flue gas flooding has more advantages than CO2 flood. From an economic viewpoint, nitrogen costs less.23-25 Also, nitrogen occupies more space in the reservoir than CO2,at the reservoir pressure. Nitrogen has lower viscosity and solubility in oil than CO2; therefore, it requires a higher pressure to achieve miscibility. The advantages of carbon dioxide flooding are that CO2 is very soluble in oils at reservoir pressure, it reduces the oil viscosity before the miscibility is achieved between the CO2 and crude oil, and the CO2 will stay dissolved in the crude oil. The minimum API gravity required is 22o API and a maximum viscosity of 10 cp for a CO2 miscible process to be applicable.
【第五段】
Chemical flooding methods require low to moderate oil viscosities and moderate to high permeability; the latter is for favourable water injection. As the screening criteria table shows, chemical floods can be used for oils that are more viscous than oils recovered by gas injection methods. Required reservoir permeability for chemical floods is higher than those required for the gas injection methods, but lower than reservoir permeability required for thermal methods. A reservoir that has an active water drive is not a good candidate for chemical flooding methods because of the low remaining oil saturation following water flooding.
【第六段】
A reservoir that has a gas cap should be carefully monitored to prevent the mobilized oil from resaturating the gas cap. The type of formation should also be considered. If the reservoir has high clay content, then it is considered unfavourable because clay will adsorb the chemicals.
【第七段】
The chemical processes are divided into polymer, alkaline, and surfactant/polymer methods. The viscosity should be less than 150 cp to use polymer processes. For higher viscosities, a higher polymer concentration is needed to achieve the desirable mobility control. Moveable oil saturation higher than 40%PV is recommended to use polymer flood. A sandstone reservoir is preferred for polymer flood application. The average permeability of the reservoir can be low as 10 md to minimize the degradation. Reservoir temperature should be less than 200o F., which limits the depth to 9000 ft
Alkaline flooding consists of injecting solutions of sodium hydroxide, sodium carbonate and sodium silicate or potassium hydroxide into the reservoir. The alkaline reacts with reservoir rock surfaces to alter wettability (oil-wet to water-wet)and reacts with acids present in the crude oil to generate a surfactant in situ that will serve to reduce interfacial tension between oil and water.35 The slug size of alkaline solutions is normally 10–15%PV and solutions concentration normally 0.2–5%.The API range is 20–35o API, oil viscosity less than 35 cp, and the average permeability is>20 md. Sandstone reservoirs are preferred.
【第八段】
Thermal methods are divided into in-situ combustion and steam flooding. In-situ combustion has been extensively field-tested. Heat is generated in the reservoir by injection of air and burning part of the crude oil. This reduces the viscosity, partially vaporizes the oil in place, and drives it forward by a combination of steam, hot water, and gas drive. The screening criteria for the process is that oil viscosity should be less than 5000 cp and API gravity should 10–20o API. For reservoir characteristics table(1),oil saturation should be greater than 50%PV,porosity should be greater than 20%and average reservoir permeability should be greater than 50 md. Sandstone formation type is also preferred.
【第九段】
Steam flooding is usually used in reservoirs containing high viscosity crude oils that are difficult to mobilize by methods other than thermal recovery. The screening criteria for steam flooding requires that the oil API gravity should be in the range of 10–20o API; oil viscosity, which is the main criteria for this process, should be greater than 5000 cp. High oil saturation is also required. For reservoir characteristics, the porosity should be greater than 10%,the permeability greater than 200 md. Sandstone formations are preferred for steam flooding applications.
【第十段】
Advancement in the application of steam injection has made it possible to apply the new technology in reservoirs that were thought to be not suitable previously. The introduction of steam assisted gravity drainage(SAGD)has transformed the huge quantities of tar sand oil in Alberta to proven oil reserves, moving Canada to second place behind only Saudi Arabia in terms of oil reserves. Some reservoirs in Kuwait contain billions of barrels of heavy oil. Some of these reservoirs consist of fractured carbonates and are prime targets for steam flooding applications. Proper management of steam flooding in these reservoirs requires careful planning and detailed studies in order to choose the appropriate steam injection scheme. Certainly the technical advances realized in drilling horizontal wells, the multilaterals, and the variations thereof have made the recovery of these heavy oil resources feasible. Various applications of SAGD have been reported in the literature39-42 and this technique certainly deserves attention for possible application in Kuwait heavy oil reservoirs. Another method that could have wide applications in fractured carbonate reservoirs is combining horizontal and multilateral wells with steam stimulation. Adding light hydrocarbons to the injected steam can also increase oil recovery by steam injection. Current oil price levels and the anticipated long-term price outlook all point to improving EOR economics of heavy oil. The accumulating experience in the Alberta tar sands will almost certainly make recovering heavy oil easier in other places including Kuwait. Because of the usual lag between study initiation and the actual application and production, it is important that an active strategy must be initiated to apply one or more of technological schemes to recover the heavy oil resources.
[ 此贴被笑韵在2007-12-10 20:19重新编辑 ]
