Layer | Fill | Outline |
---|
Map layers
Theme | Visible | Selectable | Appearance | Zoom Range (now: 0) |
---|
Fill | Stroke |
---|---|
Collaborating Authors
Results
Combined spatially resolved and non-resolved 1H-NMR relaxation analysis to assess and monitor wettability reversal in carbonate rocks
Bortolotti, Villiam (U. of Bologna) | Macini, Paolo (U. of Bologna) | Mesini, Ezio Nicola (U. of Bologna) | Srisuriyachai, Falan (U. of Bologna) | Fantazzini, Paola (U. of Bologna) | Gombia, Mirko (U. of Bologna)
Abstract Wettability is a petrophysical property that directly affects oil recovery by controlling the location, flow and distribution of fluids inside the reservoir. In this study it has been verified that a polar interaction mechanism to change wettability of a carbonate rock from water-wet to oil-wet by acid adsorption onto the rock surface can be obtained by injecting adequate chemicals, and in particular oleic acid dissolved in non-polar oil, like Soltrolยฎ 170 used for laboratory experiments. The paper deals with the assessment and monitoring of wettability reversal of carbonate rocks used in laboratory studies to evaluate the efficiency of chemical EOR methods, and in particular alkali flooding. The study is performed by combining spatially resolved and spatially non-resolved 1H-NMR information obtained on full-size cores (up to 7cm in diameter). In particular, spatially resolved quantitative NMR imaging maps (or Quantitative Relaxation Tomography, QRT) and spatially-non resolved (or Magnetic Resonance Relaxometry, MRR) analyses have been performed on full-size cores to track the process and to assess the quality of wettability reversal. Changes of relaxation time distributions and of T1 maps obtained in the experiments seem correlated with changes in wettability resulting from the chemical treatment, i.e., the contamination with oleic acid. Although further investigations are needed, MRR and QRT are promising techniques to correlate the wettability index with local values of T1 in internal sections of a rock sample. Introduction Enhanced Oil Recovery (EOR) has long been exploited in the field of oil production. EOR methods act on different reservoir aspects to increase the productivity index. In particular, the alkali EOR method deploys an injected alkaline solution that may reverse wettability to a more favourable condition for increasing efficiency of water displacement in the pores. Wettability is a petrophysical property that affects oil recovery by controlling the location, flow and distribution of fluids inside the reservoir, and plays a major role in the production of hydrocarbon, especially in water drive reservoirs. For this reason wettability received a lot of attention in laboratory studies. The concept of wettability expresses the relative adhesion of two immiscible fluids to a solid surface. In a porous medium containing two or more immiscible fluids, wettability is defined as the preferential tendency of one of the two fluids to wet the solid surface, in the sense that one of the two fluids tends to adhere better than the other one, covering it and spreading itself over the solid surface like a film. In a water-wet porous medium, in the presence of water and oil, the water occupies the smaller pores and wets most of the surface of the larger pores. In areas of higher oil saturation, the oil lies on a film of water in contact with the rock, inside the pores. In a sample of water-wet rock, the water is imbibed by the smaller pores, and may displace the oil if the sample is placed in contact with water and oil. By contrast, if the sample is oil-wet, in the presence of even a small degree of water saturation, the oil wets the rock and displaces the water. A sample saturated in oil is water-wet if it imbibes water, whereas it is oil-wet if it imbibes oil. Generally, the wettability of a rock may vary from being strongly water-wet to strongly oil-wet, depending on the interactions of the water, oil and rock. If the porous medium does not show preferential wettability to one of the two fluids, it is referred to as neutral-wet (or intermediate-wet), meaning that both fluids wet the porous medium equally [1]. Water-wet reservoir rocks can be effectively flooded by water, whereas oil-wet ones require more pore volume of water to be injected during the waterflooding in order to obtain an equivalent ultimate oil recovery [2].
- Europe (0.70)
- Asia (0.46)
- North America > United States > Texas (0.28)
- Geology > Rock Type > Sedimentary Rock > Carbonate Rock (0.82)
- Geology > Mineral (0.68)
- Reservoir Description and Dynamics > Unconventional and Complex Reservoirs > Carbonate reservoirs (1.00)
- Reservoir Description and Dynamics > Improved and Enhanced Recovery > Waterflooding (1.00)
- Reservoir Description and Dynamics > Improved and Enhanced Recovery > Chemical flooding methods (1.00)
- Reservoir Description and Dynamics > Formation Evaluation & Management > Open hole/cased hole log analysis (1.00)
Abstract Conventional alkali flooding in numerous carbonatic reservoirs is often not effective due to insufficient contact time to reverse rock wettability from oil-wet into a more favorable condition to get the highest ultimate oil recovery, i.e., water-wet or partially water-wet conditions. Therefore, conventional flooding might be not completely efficient and/or adequate. Applying intermittent flow helps rock surface to complete its wettability reversal and to improve the final oil recovery. In the present study, laboratory evaluations of alkali and Alkali-Surfactant-Polymer (ASP) flooding combined with intermittent flow are presented and comparatively discussed. An alkaline solution is injected into oil-wet homogeneous carbonatic core samples and aged for a week. This aging period represents an "intermittent flow" which allows rock surface to reach a more favorable condition for oil recovery; oil is repulsed from the rock surface and the core is then flooded by displacing brine. Core flood test is performed vertically in order to avoid the early breakthrough of injected water phase. In the solely alkali flooding, the results demonstrates that the concentration of alkali strongly affects the flooding efficiency. Alkali concentration is intentionally kept low. In fact, high alkali concentration (of about 0.5 molar) is not recommended because the insolubility of in-situ soap (soap produced by the reaction of the alkaline substance with the acid present in the oil phase) causes pore space plugging and therefore permeability reduction. The application of intermittent flow is therefore less significant in the case where high initial water saturation is present. The second part of this study emphasizes on alkali-surfactant-polymer flooding. In particular, laboratory tests highlighted that the highest final oil recovery with the lowest Water-to-Oli Ratio (WOR) is obtained by aging the alkaline solution after the injection of a surfactant, and then flooding the whole system by a polymer solution. Fractured oil-wet carbonatic reservoirs seem the best candidates for the application of this technique since aging time would allow alkali to diffuse and reverse rock wettability also in otherwise unaccessible zones. The proposed technique seems very effective to increase the ultimate oil recovery of these reservoirs. Traditionally, alkali flooding in oil-wet carbonatic reservoir is believed to require the consumption of a large mass of alkaline substances. However, the mass of this substance is responsible for the wettability reversal into a more favorable condition for oil recovery, and can be acceptably managed by a proper design of the flooding parameters. Introduction Enhanced Oil Recovery (EOR) is defined as an artificial method used to recover additional oil after the primary and secondary production. EOR is usually applied to a reservoir which is considered to have enough potential for the economical production after cost limitations have been carefully assessed. In general, EOR is conducted by injecting materials not originally present in the reservoir through an injection well. These materials cause various effects that eventually will result in a substantial improvement of the final oil recovery. Oil is collected at the same or at the adjacent wells. The purpose of EOR is not only to restore formation pressure, but also to improve oil displacement or fluid flow in the reservoir. The three major types of enhanced oil recovery operations are chemical flooding (alkaline flooding or micellar-polymer flooding), miscible displacement (carbon dioxide or hydrocarbon injection), and thermal recovery (steamflood or in-situ combustion). The optimal application of each type depends on reservoir temperature, pressure, depth, net pay, permeability, residual oil and water saturations, porosity and fluid properties such as oil API gravity and viscosity.
- Europe (0.68)
- Asia (0.46)
- North America > United States (0.29)
Abstract Intermittent alkali flooding can significantly enhance oil recovery in oil-wet carbonate reservoirs. The method basically acts in two ways, by reducing the interfacial tension between the reservoir fluids and by reversing the wettability to a more favorable condition. However, the reversal of wettability requires aging time to reach the equilibrium. An intermittent or a pausing period is then adopted for the proposed alkali flooding process to let the surface reaching the maximum favorable wettability. As the injected fluid is paused during the flood process, vertical or inclined reservoirs are more suitable for this combination because the water tongue effect does not cause an early breakthrough. Laboratory results show that one-week-intermittent alkali flooding in homogeneous carbonate rock yields greater oil recovery, about 10 percent larger than conventional continuous alkali flooding in a proper range of injected alkali concentration. Low alkali concentration causes quick alkali depletion as time increases, while high alkali concentration causes pore plugging by in-situ precipitation of insoluble soap. The alkalinity of injected fluid should be kept as high as possible. Therefore, a strong alkali such as sodium hydroxide is recommended. High acid concentration in crude drives in-situ saponification frontward; hence, alkali concentration range should be carefully studied. Normally, high initial water saturation prevents the system from alkali accumulation and, as a consequence, insoluble soap precipitation is less concerned. Fractured carbonate reservoirs are probably the most suitable candidates for the application of this technique, since aging time would allow alkali to diffuse to, and reverse the wettability of the inaccessible and unswept zones. The proposed technique seems very effective to increase the ultimate oil recovery in oilwet carbonate reservoir. The drawbacks seem acceptable and the expected results are promising. Introduction The best practices of petroleum production suggest that oil is first produced by primary recovery by means of natural drive mechanisms. After a certain period of production, the natural drive decreases and eventually large amount of oil cannot be recovered. Prolonging the production will not yield further economical results, unless secondary recovery and/or Enhanced Oil Recovery (EOR) are utilized to extend the productive life of the reservoir. Secondary recovery (mostly waterflood) is performed by injecting water (normally natural, artificial, or sea brine) below the water table. Additional oil is released from the reservoir rock by waterflood pressure that overcomes the oil-entrapped capillary force. Some reservoirs may not respond to waterflood because of the unfavorable reservoir characteristics and of the overall geological conditions. The ultimate oil recovery after primary and secondary recovery is less than 40% of the Original Oil In Place (OOIP) in most reservoirs 1. EOR may thus be chosen to improve oil recovery. EOR, also called tertiary recovery, is performed by injecting fluid materials that are absent in the reservoir 2. EOR is not necessarily performed after the water flooding phase. An EOR method can be designed after primary recovery when waterflood is expected to give uneconomical results, or even waterflood can be adopted since the early production phase. Amongst conventional EOR methods are steam flooding, miscible flooding (e.g. CO2 injection), and immiscible flooding (injection of polymer, surfactant, alkali, gel, and foam). Nowadays, each method has been modified to suit the requirements of specific reservoir conditions. Alkali flooding has been investigated since 1917. Alkaline substances are quite inexpensive, but this technique normally yields questionable results. Sodium hydroxide is the most commonly used alkali because it shows the highest efficieny amongst other alkaline substances. Alkali display several actions to improve the oil recovery when they are injected into the reservoir. The most noticed phenomena taking place during the displacement of alkali in reservoir rocks are a) Interfacial Tension (IFT) reduction of reservoir fluids by acid-base interaction and b) wettability changes of rock matrix. Normally, the injected alkaline solution reacts with the natural acid substances existing in the crude oil phase to form in-situ surfactant at the interface, which causes spontaneous emulsification. Moreover, the injected alkali reacts as well with the rock matrix and eventually the wettability characteristic turns into a more favorable condition for the water displacement process.
- Europe (0.46)
- North America > United States (0.46)
- Geology > Geological Subdiscipline (0.48)
- Geology > Mineral (0.46)
- Geology > Rock Type > Sedimentary Rock > Carbonate Rock (0.34)
- Reservoir Description and Dynamics > Unconventional and Complex Reservoirs > Carbonate reservoirs (1.00)
- Reservoir Description and Dynamics > Improved and Enhanced Recovery > Waterflooding (1.00)
- Reservoir Description and Dynamics > Improved and Enhanced Recovery > Chemical flooding methods (1.00)