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Research Papers: Petroleum Wells-Drilling/Production/Construction

Propagation of Regular HCl Acids in Carbonate Rocks: The Impact of an In Situ Gelled Acid Stage

[+] Author and Article Information
Ahmed M. Gomaa

 Petroleum Engineering Department Texas A&M University 507 Richardson Building, College Station, TX 77843ahmed.gomaa@pe.tamu.edu

Hisham A. Nasr-El-Din

 Petroleum Engineering Department Texas A&M University 507 Richardson Building, College Station, TX 77843hisham.nasreldin@pe.tamu.edu

J. Energy Resour. Technol 133(2), 023101 (May 26, 2011) (9 pages) doi:10.1115/1.4004027 History: Received October 13, 2010; Revised March 30, 2011; Published May 26, 2011; Online May 26, 2011

Recent laboratory and field studies indicated that polymer-based in situ gelled acids can cause formation damage. Coreflood experiments using single-stage and multistage acids were conducted at 250 °F. 15 wt. % regular HCl and 5 wt. % in situ gelled acid-based on Fe(III) as a crosslinker were the acids that were used in this study. Propagation of acids and crosslinker inside 20 in. long cores was examined for the first time in detail. Stage volume and injection rate, which were the parameters that affect the propagating of various chemical species, were examined. Samples of the core effluent were collected and the concentrations of calcium, crosslinker, and acid were measured. Material balance was conducted to determine the amount of cross-liker that retained in the core. The results show that in situ gelled acid should be pumped at low injection rates. In situ gelled acid at low injection rate instantaneously plugged the tip of the wormhole and did not create additional wormholes inside the core. Therefore, when the final regular acid stage bypassed the gel, it started to propagate from nearly the last point that the first stage ended. In site gelled acid stage volume should not exceed 0.5 PV. No benefits were gained by increasing the volume of in situ gelled acids. Retention of total iron in the core increased in multistage acid treatments, especially at low acid injection rates.

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Copyright © 2011 by American Society of Mechanical Engineers
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References

Figures

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Figure 1

Normalized pressure drop across cores# 1 and 2 during injection of 15 wt. % regular HCl at 5 and 20 cm3 /min, T = 250 °F

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Figure 2

Normalized pressure drop across cores# 3 and 4 during the injection of 5 wt. % in situ gelled at 5 and 20 cm3 /min, T = 250 °F

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Figure 3

Pressure drop across core# 5 during the injection of three acid stages at 5 cm3 /min and T = 250 °F

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Figure 4

A schematic diagram describes the performance of the regular and in situ gelled acids inside the cores

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Figure 5

Pressure drop across core# 6 during the injection of three acid stages at 5 cm3 /min and T = 250 °F

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Figure 6

pH value and density of the core effluent samples, T = 250 °F, core# 5

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Figure 7

pH value and density of the core effluent samples, T = 250 °F, core 6

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Figure 8

Total calcium and iron concentrations in the core effluent samples, T = 250 °F, core# 5

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Figure 9

Total calcium and iron concentrations in the core effluent samples, T = 250 °F, core# 6

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Figure 10

Pressure drop across core# 7 during the injection of three acid stages at 20 cm3 /min and T = 250 °F

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Figure 11

Pressure drop across core# 8 during the injection of three acid stages at 20 cm3 /min and T = 250 °F

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