Effect of Oil Saturation on the Flow of Emulsified Acids in Carbonate Rocks
- Mohammed A. Sayed (Aramco Services Company) | Ahmed I. Assem (Texas A&M University) | Hisham A. Nasr-El-Din (Texas A&M University)
- Document ID
- Society of Petroleum Engineers
- SPE Production & Operations
- Publication Date
- February 2014
- Document Type
- Journal Paper
- 29 - 41
- 2014.Society of Petroleum Engineers
- 3.2.4 Acidising, 4.1.2 Separation and Treating, 5.2.1 Phase Behavior and PVT Measurements, 5.8.7 Carbonate Reservoir
- wormholes, emulsified acid, acidizing, acid propagation, droplet size
- 2 in the last 30 days
- 495 since 2007
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Matrix acid treatments in carbonate reservoirs target stimulation of the near-well region. Emulsified acid can be used in matrix acidizing and acid-fracturing treatments. The delayed nature of emulsified acid is useful in creating deep wormholes and etched fracture surfaces. Almost all previous coreflood work was performed on cores fully saturated with water. Therefore, the main objective of the present work is to study the effect of oil saturation in the formation on the flow of emulsified acids in carbonate cores and assess the performance of emulsified acid in stimulating carbonate formations. A coreflood study was conducted using Indiana limestone cores that were 1.5 in. in diameter and 6 in. in length. The effect of the presence of crude oil on the volume of acid to breakthrough was studied. Also, the size, number, and distribution of the wormholes were determined with computed-tomography (CT) images. The effect of the acid injection rate on the performance of emulsified acid was investigated. Cores that were fully saturated with water, fully saturated with crude oil, and saturated with crude oil at irreducible water saturation were used. There was no optimum injection rate for emulsified acids when they were injected into Indiana limestone cores with permeabilities of 47 to 238 md. In such a range of permeability, emulsified acid enhanced the rock permeability when the acid was injected at both high (10.0 cm3/min) and low (0.5 cm3/min) rates. For cores fully saturated with crude oil, the volume of emulsified acid to achieve breakthrough was 2.2 times more than that required to achieve breakthrough in cores fully saturated with water. The increase in emulsified-acid volume refers to the increase in the volume of the continuous phase resulting from the mixture of the crude oil and diesel and the subsequent change in the acid/diesel volume fraction. As a result, more acid was consumed to create wormholes and achieve the breakthrough. The emulsified-acid system was effective in stimulating limestone cores, whether these cores were saturated with water, oil, or oil at irreducible water saturation.
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