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Fractured Carbonate
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APPLICATIONS » According to the DOE, 22% OOIP of entire U.S. oil reserves are shallow shelf carbonate reservoirs. About 80% of carbonate reservoirs are classified as neutral to oil-wet (Standnes and Austand, 2002), and an oil-wetting condition is even more likely to be the case in cooler, more shallow reservoirs (Austad and Standnes, 2002).
Ordinary waterflood operations often have very poor recovery (20% or less of OOIP) in fractured carbonate reservoirs. The root cause is that injected water will not imbibe into the matrix portion of the reservoir, being oil-wet. This means that chemical formulations that can successfully alter carbonate mineral surfaces from oil- to water-wet condition – and which can penetrate the matrix porosity feeding natural fractures – can be effective EOR agents in a large number of oil reservoirs. For example, there are many large, shallow (cooler, less than 50 C), carbonate reservoirs in the Permian Basin which have all of the characteristics of potential candidates for this chemical EOR process. Attributes of candidate reservoirs are as follows:
- Mature waterfloods with poor recovery
- Fractured formations or formations having significant thief zones
- High oil saturation remaining in the porous matrix due to its oil-wet condition.
Adding the right surfactants to the injection water will modify wettability of the carbonate reservoir to a water-wet condition and decrease the interfacial tension (IFT) – thereby increasing the penetration of the injected aqueous phase into the rock matrix in which oil is trapped. The previously immobile oil is forced out of the oil-rich matrix as aqueous (chemical) solution imbibes – and enters the fracture/high permeability flow network. These flow networks act as a “highway” to transport the newly mobilized oil to production wells. If properly designed, this process will significantly increase the recovery of oil otherwise left behind by the waterflood.
- SurFlood CRS » Carbonate Reservoir Surfactant Technology for IOR / EOR
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SurFlood CRS »
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Adding the right surfactants to the injection water will change the wettability of the carbonate reservoir surfaces to a water-wet condition and decrease the interfacial tension so as to increase the penetration of the injected aqueous phase into the rock matrix holding trapped oil. The effect of time on oil recovery from carbonate core by 0.2% SurFlood CRS was demonstrated, see Figure 1. . |
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Figure 1. Oil Recovery from Carbonate Core vs. Time |
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SurFlood CRS is a formulated with cost-effective chemicals to provide oil penetration and spontaneous imbibition of injection or treatment water into oil-rich reservoir matrix regions via altering the wettability from an oil-wet to a water-wet state , see Figure 2. |
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Figure 2. Demonstration of Surface Cleaning Effect with SurFlood CRS |
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This product will recover incremental oil beyond a waterflood operation from carbonate reservoirs (Figure 3). The product considers the fundamental mechanism of oil components (e.g. naphthenic acid) that induce oil-wetting on carbonates and how surfactant solutions then have the desirable function of reversing the surface to become water-wet. The typical heavy and light oil samples from Permian Basin were used in developing the system. The specific target for this improved technology will be large, domestic carbonate reservoirs that are at a mature point in their waterflood operations, most especially those that are fractured reservoirs and with the matrix blocks in an oil-wet state. For such reservoirs, the waterflood is usually very inefficient, in part, because the injection water can not imbibe into the porous, matrix blocks due to their oil-wet condition. |
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| Figure 3. Spontaneous Expulsion of Oil with SurFlood CRS Treatment |
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