Improved Oil Recovery from Carbonate Reservoirs by Chemical Stimulation
- Xina Xie (INL & Correlations Co) | William W. Weiss (Correlations Co.) | Zhengxin J. Tong (U. of Wyoming) | Norman R. Morrow (U. of Wyoming)
- Document ID
- Society of Petroleum Engineers
- SPE Journal
- Publication Date
- September 2005
- Document Type
- Journal Paper
- 276 - 285
- 2005. Society of Petroleum Engineers
- 7.6.6 Artificial Intelligence, 6.5.2 Water use, produced water discharge and disposal, 5.4.1 Waterflooding, 1.6.9 Coring, Fishing, 5.8.7 Carbonate Reservoir, 3.2.4 Acidising, 4.1.2 Separation and Treating, 2.5.2 Fracturing Materials (Fluids, Proppant), 5.8.6 Naturally Fractured Reservoir, 4.3.3 Aspaltenes, 1.2.3 Rock properties
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Oil reserves from shallow-shelf carbonate reservoirs account for 22% of theoriginal oil in place (OOIP) of the entire U.S. oil resource. Many of thesereservoirs are naturally fractured. A pressure-pulsing technique has been usedin fractured fields to improve oil recovery. In some situations, imbibition ofwater can be promoted by chemical stimulation to alter the reservoirwettability toward water-wetness such that oil is expelled at an economic ratefrom the rock matrix into fractures. Shallow-shelf (i.e., Class II) carbonatereservoirs typically produce less than 10% OOIP during primary recovery andrespond poorly to water injection.
In this work, promotion of imbibition was determined for a cationicsurfactant, cocoalkyltrimethyl ammonium chloride (CAC), and a nonionicsurfactant, an ethoxylated alcohol (POA).Cores from three dolomitic ClassII reservoirs, Cottonwood Creek, Dagger Draw, and Lustre, were used in thelaboratory tests. After preparing core samples using the correspondingreservoir crude oil and brine, spontaneous expulsion of oil was measured inglass imbibition cells at elevated temperature for more than 50 core samples.When reservoir brine was used as the imbibition fluid, oil recovery was in therange of 0 to 35% OOIP. After imbibition of reservoir brine had ceased, thecores were transferred into surfactant solutions at or somewhat above thecritical micelle concentration (CMC) to test for enhanced recovery by furtherimbibition. Typically, immersion in the surfactant solution resulted in anadditional recovery of 5 to 10% OOIP. The increased recovery is mainly ascribedto increased water--wetness. The effect of acidization before surfactanttreatment was also tested and found to be detrimental to oilrecovery.
Approximately 22% of the OOIP of the entire U.S. oil reserves resides inshallow-shelf carbonate reservoirs. Most of such reservoirs are heterogeneousand naturally fractured. Attempts to displace oil by waterflooding posesignificant problems because the fractures lead to bypassing of the rock matrixand early breakthrough. Spontaneous imbibition can be of special importance tooil recovery from fractured reservoirs.1-3 However, spontaneous imbibition onlyoccurs when the pore surfaces are effectively water-wet so that water imbibesinto the rock matrix and oil is expelled into the fractures. The oil can thenbe flushed along the fractures toward the production wellbore.
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