Gas injection into oil reservoirs is one of a many critical activities to strengthen pot that can pledge a solid prolongation from a field. On time injection of adequate gas can redeem billions barrels of oil. In addition, it can safety a large volume of gas for successive generations.
Gas injection has been complicated in fact in a petroleum literature. For example, Parvizi et al. (2014) complicated an initial review of a sobriety drainage during immiscible gas flooding in a carbonate formation. In their study, nitrogen gas was injected into a singular pattern retard during opposite rates and directions. Their regulation showed that gas injection during sobriety drainage rate gives a limit ransom Moreover, a ultimate ransom decreases during many aloft injection rates.
There are really good reviews on CO2 flooding during EOR, e.g. Manrique et al. complicated a margin practice during EOR in a carbonate fountainhead of a United States (Manrique et al., 2006). They indicated that CO2 flooding (i.e. continual or H2O swap gas injection (WAG)) is a widespread EOR routine in a United States. Hawez et al. showed that CO2 injection next a smallest miscibility vigour (MMP) takes too prolonged time to contend fountainhead vigour (Hawez et al., 2014). Moradi et al. experimentally complicated a water-based nanofluid swapping gas injection as a novel EOR (Moradi et al., 2015). In their study, a smaller nano-size particles had a softened recovery. Ghafoori et al. investigated N2 and CO2 WAG flooding in a carbonate arrangement (Ghafoori et al., 2012). The regulation showed that to optimize a ransom of CO2 flooding, a continual gas knock followed by a WAG flooding is required. There are also many studies dedicated to gas flooding with opposite compositions. Syzdykov complicated gas injection opening in a low-permeability gas-condensate arrangement (Syzdykov, 2007). The regulation suggested that injecting a reduction of 50% C1and 50% N2 into a tip partial of a carbonate formation, starting as early as possible, regulation in a tip recovery. Ebrahimi et al. investigated hydrocarbon and non-hydrocarbon (i.e. CO2 and N2) flooding into one of a Iranian oilfields (Ebrahimi et al., 2012). A compositional fountainhead simulator was implemented to weigh a oil ransom of that field. Abedini et al. investigated a opening of immiscible and miscible CO2 injection in a parsimonious carbonate arrangement regulating both initial and make-believe approaches (Abedini et al., 2015). In that study, many attempts were done to story compare a initial results. Wang et al. complicated a effects of impurities on CO2 transport, injection, and storage. A elementary regulation has been grown to capacitate discerning integrity of CO2 injectivity a outcome (Wang et al., 2011).
Previous practice showed that gas injection could be implemented in parsimonious formations. For example, Zhao et al. introduced CO2 flooding in plane wells of Ordos Basin parsimonious oil reservoir. They showed that this EOR routine could be useful for a fast and effective growth of parsimonious oil reservoirs in Ordos Basin (Zhao et al., 2016). Moreover, Abedini et al. complicated a opening of immiscible and miscible CO2 injection processes in a parsimonious carbonate reservoir. All a exam regulation were unnatural regulating a CMG package, and try was done to story compare a initial regulation (Abedini et al., 2015).
During miscible gas injection, one of a many pivotal factors that needs to be evaluated rightly is a research of smallest miscibility vigour (MMP). In a literature, many extensive studies were conducted to weigh MMP. For example, Shahrabadi et al. complicated a outcome of CO2 thoroughness in injecting gas on MMP. Some banishment tests regulating slim tube apparatus were achieved and recoveries and MMP’s were measured. Finally, a initial regulation were compared with a indication predictions. Good agreement was achieved between a initial information and indication predictions (Shahrabadi et al., 2012). Moreover, Motaleby Nedjad et al. complicated a integrity of MMP by an methodical method. In their study, they due a routine for elucidate a multi-component complement formed on a methodical calculation of ternary systems, that simplifies and translates a multi member complement into a pseudo ternary complement and estimates a smallest miscibility vigour though elucidate formidable and time immoderate equations of crossover tie lines (Motaleby Nedjad et al., 2007). Furthermore, Akbari et al. complicated a integrity of MMP in a gas injection routine by regulating ANN with several blending rules. Comparing a commission blunder of this indication to those of a prior novel information showed that a regulation performed from a new MMP indication were some-more accurate (Akbari et al., 2012). Finally, Jaubert et al. in their studies resolved that when a injected gas was not pristine CO2, it was adequate to fit usually dual parameters of a equation of state on data, including exemplary PVT and flourishing data, and afterwards they used them to envision a MMP. The correctness performed was identical to a initial doubt (Jaubert et al., 2014).
In this study, initial a PVTi program is implemented to weigh a miscibility of opposite forms of injected gas, including CO dioxide, nitrogen, methane, and some mixtures of hydrocarbon gases with opposite proportions. Subsequently, E-300 program package is used to envision a ransom of a injected gases into a arrangement underneath investigate from one of a Iranian onshore fields. Finding a best flooding unfolding (i.e. a optimized scenario) with courtesy to fit gas type, time of flooding, and injection plcae is a primary goals of this research.
۲-Case study, fountainhead data
The fountainhead underneath investigate is located in a southwest of Iran and has a length of 34 kilometers, a breadth of 28 kilometers, and a tallness of 500 meters (Figure 1). The make-believe indication is stoical of grids with a distance of 2500×۲۵۰۰×۳۰۰ ft. To do a simulations, a zone of this margin indication was deliberate that has 5×۵×۳ grids. The fountainhead contains dual wells, namely one prolongation and one injection well. The former produces by all layers, i.e. full penetration, and a after injects gas into a bottom covering of a formation.
The geological indication of a margin underneath study: a placement of fountainhead permeability opposite a formation.
The fountainhead liquid underneath investigate is a compositional type. The fountainhead heat is 150 °F, and a initial vigour was 4000 psia; a normal permeability of a fountainhead is 100 mD, and a porosity is 0.11. Figure 2 depicts a relations permeability and capillary vigour of a categorical stone form of a reservoir. As it can be seen, a cranky territory of both relations permeability curves is during a superfluity value around 50%. Therefore, we can qualitatively contend that this arrangement has a neutral wettability. Table 1 shows a components of a liquid representation and their properties. Prior to a compositional modelling in E300, we should balance a equation of a state (EOS). To indication a liquid behavior, a EOS of Peng-Robinson was implemented in PVTi. This EOS is so renouned in a petroleum industries and can envision a proviso function of petroleum fluids really good (Ramdharee et al., 2013). There are so many studies in a petroleum novel that have successfully implemented this EOS in their analyses (Song Wei et al., 2000; Nasri et al., 2009).
Different analyses were deliberate during a tuning of EOS, including consistent combination expansion, differential liberation, and burble indicate vigour exam in PVTi software. The proviso blueprint of a PVT representation after a tuning is decorated in Figure 3. To speed-up a simulations, some of a components were lumped together (Figure 4). To envision viscosity, a Lohrenz-Bray-Clark association was implemented.
Relative permeability and capillary vigour information of a fountainhead underneath study; a fountainhead stone has a neutral wettability condition.
Reservoir liquid components and their parameters.
As an example, Figures 5 and 6 uncover a tuning regulation successive to a tuning routine for consistent combination enlargement (CCE) and differential ransom (DL) tests. As indicated, there is a good compare between a initial regulation and a EOS predictions, that was performed by changing a weight factors of a tests as good as a properties of a and fractions and binary communication coefficients.
Phase function of a fountainhead fluid.
Ternary tract of a fountainhead member formed on organisation of C1, C2-C6, and C7+.
۳٫ Results and discussion
۳٫۱٫ MMP determination
The initial theatre of a investigate was a integrity of MMP during initial hit (FCM) and mixed contacts (MCM) for opposite injected gases. At a consistent heat and composition, a lowest vigour during that miscibility (dynamic miscibility) can be achieved around initial or mixed contacts is called MMP. At MMP, a interfacial tragedy is zero, and no interface exists between a fluids.
Table 2 shows a outcome of a MMP determination. As it can be indicated, opposite gases with a far-reaching operation of compositions from pristine methane and CO2 to a movement of lighter components were deliberate during a MMP estimation. Our regulation showed that a injected reduction gas containing 90% C1 and 10% C2 has a aloft MMP, while a injected gas stoical of 100% CO2 has a lowest MMP value.
Methane and ethane are hydrocarbon gases and can be miscible in fountainhead components during a suitable vigour and temperature. In contrary, N2 and CO2 are immiscible during low pressures given these gases are non-hydrocarbon. At a low pressure, they can pull a fountainhead fluids and assistance production. According to Table 2, for a miscible injection during a initial vigour of fountainhead (4000 psia), a reduction of 50% C1 and 50% C2 is a best unfolding given a MMP of this gas is really tighten to a arrangement pressure.
Relative volume of oil to gas during opposite pressures.
Gas to oil ratio contra arrangement pressure.
The regulation of FCM and MCM with opposite gas injection components.
۳٫۲٫ Investigation of opposite gas flooding scenarios
At a early theatre of a fountainhead life, a prolongation was achieved by healthy production, while during after times, gas flooding started. Reservoir make-believe can establish a opening of a fountainhead during a prolongation duration by anticipating a arrangement pivotal parameters, e.g. fountainhead efficiency, margin prolongation rate, margin vigour etc. Figure 7 shows a outcome of all gas flooding scenarios mentioned in Table 2. Subsequent to about 4000-day prolongation with healthy mechanism, miscible gas flooding was started to urge a recovery. If we continue with healthy production, a ultimate ransom of about 27% can be achieved by a fountainhead life. Among a injected gases, a make-believe regulation suggested that a CO2-flooding potency (82%) was a best among all a other scenarios for a prolonged prolongation period. Nevertheless, in a early and center stages of flooding (until 25 years after a initial production), a gas-flooding unfolding with a reduction of 50% ethane and 50% methane with a ransom cause of 0.77 could be a best plan. Moreover, during early and center stages, a N2 flooding had a best vigour upkeep in this reservoir, though a potency of this flooding was not so opposite from a other gas flooding scenarios later. Furthermore, a hybrid flooding of gases during opposite time intervals competence have softened results, that needs serve investigations.
Field potency during opposite gas flooding scenarios; a injection scenarios were started after 4000 day healthy prolongation from a field.
According to a PVT results, in a flooding box of a reduction of 50% C1 and 50% C2, a injected liquid could be miscible during a vigour reduction than a burble indicate of a sample. Therefore, implementing liquid compositions that have a aloft C2/C1 ratio was not suitable since gases containing heavier components are not so economic. According to a results, during aloft fountainhead pressures, reduce C2 fractions in a injected gas can be implemented. In this situation, gas flooding can be miscible (or semi-miscible) and can have a best performance.
The ultimate ransom cause from opposite gas flooding scenarios.
Nitrogen as good as a other non-hydrocarbon gases behaves a same as methane.
Figure 7 depicts a margin vigour for opposite gas flooding scenarios. In a injection good of all a scenarios, a gases are injected during a consistent vigour of 4000 psi, and about 15000 MSCF of gas was injected. Figure 8 shows that during a early and center stages of a flooding process, a N2 flooding has a best fountainhead vigour maintenance. However, during a after time, a potency of this flooding is not so opposite from flooding by a other gases.
Field vigour during opposite gas flooding scenarios; a start indicate of gas injections is around 4000 days.
Figure 9 compares a opposite flooding scenarios together. In dual scenarios, a CO2 injection and C1 injections were started successive to 10-year healthy production, while there is another scenario, in that a CO2 flooding was started with a 12-year loiter following to a healthy prolongation (the injection starts after 22 years of healthy production). According to this figure, a CO2 flooding following to a 22-years healthy prolongation can have a same potency as a box with 10-years of methane flooding. This is engaging as a final ransom of these dual scenarios is in a same order, while a expenditure of a injected gases is so opposite from any other. Thus, instead of methane flooding during early stages, we can continue with healthy prolongation until a center flooding stages (in this case, equal to double of a healthy prolongation time), and afterwards we can inject CO2. These dual scenarios will have a same potency in prolonged time intervals.
Field potency (recovery cause fraction) for CO2 and C1 flooding during opposite stages of a fountainhead life.
The many appealing unfolding is a CO2 flooding as this gas is miscible with a arrangement fluid. Lower gas-oil ratio during CO2 flooding is an indicator that this gas is some-more miscible than a other fluids deliberate herein; this function is shown in Figure 10.
Field gas to oil ratio for opposite gas flooding scenarios; miscible flooding scenarios uncover reduction GOR or reduction gas breakthrough.
In a aspect of water-cut of a prolongation well, a CO2 flooding showed softened potency by reduction H2O producing (Figure 11), while a N2 flooding had a misfortune potency among all scenarios. It is value mentioning that a fountainhead indication does not enclose any aquifer or H2O injection well.
Field sum H2O cut during opposite flooding scenarios.
۳٫۳٫ Finding best gas injection rate
In this attraction analysis, gas is injected during opposite rates to urge a fountainhead efficiency. Gas can be injected in opposite layers. In fact, gas should be injected into a reduce active layers, where a permeability is higher, and a gas can be in hit with a oil proviso for a longer time. If a gas flooding routine is miscible, there is no opposite between a tip or bottom covering of a fountainhead in a box of equal covering permeability. By lifting a injection rate from 1000 to 5000 bbl/D, fountainhead potency was softened (Figure 12 and Table 4).
۳٫۴٫ Investigation of gas flooding in opposite layers
Gas injection can be influenced by a plcae of a injection into fountainhead layers, porosity, permeability, accessibility of faults etc. Injecting a gas into a bottom covering of a fountainhead can pull a fountainhead oil adult to a prolongation well. Injecting a gas into a center covering distributes a gas to a tip layers, so it can be suitable for a miscible process. Finally, injecting a gas into a tip layers has a risk of augmenting a gas-oil ratio in a prolongation well. Figure 13 illustrates gas flooding in opposite layers of a arrangement underneath study.
While a gas-flooding routine is miscible, there is no disproportion between injections into a tip or bottom layers. Therefore, gas injection into a high-permeability layers of a fountainhead or deeper layers is recommended. While a injected gas moves toward a prolongation wells, it can be in hit with some-more oil phase. Thus, a miscibility processes can be speeded up.
Field potency after CO2 flooding during opposite rates.
Field potency during opposite CO2 flooding rates after 14000 days.
Field potency after CO2 flooding into opposite layers of arrangement underneath study.
In this study, a best gas-flooding unfolding with a tip potency was deliberate in details. The MMP determination of several gasses with opposite components was analyzed as well. The regulation suggested that during a brief and center theatre of a fountainhead life, a miscible gas stoical of 50% C1 and 50% C2 had a tip recovery; however, a final ransom value is not so opposite from pristine methane flooding. In addition, a potency of injecting 100% C1 by all fountainhead life is homogeneous to a miscible CO2 flooding from a center theatre of a fountainhead life. The CO2 flooding was softened than other gas injection scenarios in a prolonged injection period. Furthermore, it has been investigated that injecting gas during opposite rates could urge a fountainhead efficiency; methane is a inexpensive and permitted gas compared to a others, so, during early stages, it should be softened for injection in a reservoir, while during after stages CO2 has a best efficiency; however, CO2 is not suitable for Iranian reservoirs, so we should inject methane. Nonetheless, high injection rates should be avoided. The regulation showed that a covering where a gas is being injected is also of a primary importance. It is softened to inject a gas into a active layers of a fountainhead with aloft permeability and aloft depths. According to a results, we can also name a best unfolding during early stages and in a prolonged duration of time after gas injection.
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