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Difference between revisions of "Conducting the acidizing procedure"

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== On-site evaluation of acid treatment effectiveness ==
 
== On-site evaluation of acid treatment effectiveness ==
The pressure and rate chart of the acid treatment show the effect of acid volume on the formation as the acid treatment proceeds. The papers of McLeod and Coulter, <ref name="r2" /> Paccaloni ''et al.'', <ref name="r3" /> and Prouvost and Economides<ref name="r4" /> are significant to the on-site evaluation of acidizing treatments. On-site data monitoring follows and evaluates the progress of damage removal by acid. '''Fig. 3'''<ref name="r3" /> shows injection rate and pressure plotted on a precalculated chart of pressure vs. rate and crossplotted with a family of skin-factor curves based on steady-state injection. The successive points clearly show the reduction in skin factor. These plots may be somewhat misleading because pressure transients are ignored after rate changes; however, no on-site computer is required.  
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The pressure and rate chart of the acid treatment show the effect of acid volume on the formation as the acid treatment proceeds. The papers of McLeod and Coulter, <ref name="r2" /> Paccaloni ''et al.'', <ref name="r3" /><ref name="r16"><ref name="r17"> and Prouvost and Economides<ref name="r4" /> are significant to the on-site evaluation of acidizing treatments. On-site data monitoring follows and evaluates the progress of damage removal by acid. '''Fig. 3'''<ref name="r3" /> shows injection rate and pressure plotted on a precalculated chart of pressure vs. rate and crossplotted with a family of skin-factor curves based on steady-state injection. The successive points clearly show the reduction in skin factor. These plots may be somewhat misleading because pressure transients are ignored after rate changes; however, no on-site computer is required.  
  
 
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<ref name="r15" >Gdanski, R.D. and Shuchart, C.E. 1998. Advanced Sandstone-Acidizing Designs With Improved Radial Models. ''SPE Prod & Fac'' '''13''' (4): 272–278. SPE-52397-PA. http://dx.doi.org/10.2118/52397-PA. </ref>
 
<ref name="r15" >Gdanski, R.D. and Shuchart, C.E. 1998. Advanced Sandstone-Acidizing Designs With Improved Radial Models. ''SPE Prod & Fac'' '''13''' (4): 272–278. SPE-52397-PA. http://dx.doi.org/10.2118/52397-PA. </ref>
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<ref name="r16" >Paccaloni, G. 1979. New Method Proves Value of Stimulation Planning. ''Oil & Gas J.'' 19 Nov. pp. 155-60 <ref />
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<ref name="r17" >Paccaloni, G. 1979. Field History Verifies Control, Evaluation. ''Oil & Gas J.'' 26 Nov. pp. 61-65 <ref />
 
</references>
 
</references>
  

Revision as of 13:34, 25 March 2014

You've decided that your well is a good candidate for acidizing, assessed the formation, designed the treatment, prepared the well and equipment, so now you're ready to conduct the treatment. This page describes both the process and things you should be doing during and immediately after the treatment.

Injection-rate control and monitoring

The main acid job should be circulated in place with HCl acid placed across the formation before the packer is set or before the bypass valve is closed. All perforations should be covered by acid before injection starts. Injection should start at a predetermined injection rate and the pressure observed to determine the condition of the wellbore. If the pressure rises close to the pressure limit, the rate should be cut in half until the pressure stabilizes at a level below the formation fracturing pressure. When the HF acid stage reaches the formation, a pressure drop is normally observed. The rate should not be changed as long as a positive pressure is observed at the wellhead. If the well goes on vacuum, the rate should be instantly raised until a positive pressure is observed at the wellhead. Hold the new rate steady as the acid is injected. Nevertheless, the constant injection rate of HF acid into the wellbore should not exceed an optimum 1/2 bbl/min unless the perforated interval is greater than 25 ft. If the formation is very thick, the rate can be 0.02 bbl/min per foot of net pay. Other authors have different opinions on allowable injection rates, as discussed later.

Pressure behavior during acid injection

Two pressure responses are often observed during acid treatment. Fig. 1 shows one response. [1] In this well, when acid hit the formation, pressure dropped immediately. As the pressure dropped, the rate was increased; then the pressure began to rise. The rate was reduced, and then the well was shut in while another batch of acid was mixed on site. Injection was restarted at a rate of 2 bbl/min, then cut back to 1.5 bbl/min and stabilized at 2 bbl/min for the final injection of overflush. Rate should be held constant for a period of time at least until the pressure stabilizes. Haphazard changes in rate make it impossible to determine on site what the quantitative response of the well is to the acid treatment, unless newer computer models and monitoring equipment are available, as discussed later. A better-controlled acid treatment is shown in Fig. 2. [1] Here, the rate is stabilized at 0.55 bbl/min. When the HF acid stage entered the formation, the pressure slowly declined but stayed above 0 psi. This rate was continued as long as the pressure was observed and is the type of response that one should observe when a well is treated to remove wellbore damage.

When the overflush reaches the formation, the rate may be increased as fast as allowed, as long as the pressure stays below the fracturing pressure. The faster overflush rate will push the spent acid deeper into the formation and overdisplace the spent acid reaction products more efficiently away from the wellbore. This safely finishes the treatment and allows the spent acid to be produced back sooner. The well should be flowed immediately, unloaded with nitrogen, swabbed back, or put on artificial lift.

When the overflush reaches the formation, the rate may be increased as fast as allowed, as long as the pressure stays below the fracturing pressure. The faster overflush rate will push the spent acid deeper into the formation and overdisplace the spent acid reaction products more efficiently away from the wellbore. This safely finishes the treatment and allows the spent acid to be produced back sooner. The well should be flowed immediately, unloaded with nitrogen, swabbed back, or put on artificial lift.

On-site evaluation of acid treatment effectiveness

The pressure and rate chart of the acid treatment show the effect of acid volume on the formation as the acid treatment proceeds. The papers of McLeod and Coulter, [2] Paccaloni et al., [3]Cite error: Closing </ref> missing for <ref> tag

[2]

[3]

[4]

[5]

[6]

[7]

[8]

[9]

[10]

[11]

[12]

[13]

[14]

[15]

<ref name="r16" >Paccaloni, G. 1979. New Method Proves Value of Stimulation Planning. Oil & Gas J. 19 Nov. pp. 155-60 Cite error: The opening <ref> tag is malformed or has a bad name

<ref name="r17" >Paccaloni, G. 1979. Field History Verifies Control, Evaluation. Oil & Gas J. 26 Nov. pp. 61-65 Cite error: The opening <ref> tag is malformed or has a bad name </references>

Noteworthy papers in OnePetro

Use this section to list papers in OnePetro that a reader who wants to learn more should definitely read

External links

Use this section to provide links to relevant material on websites other than PetroWiki and OnePetro

See also

Evaluation of acid treatments

Acid treatment design

Acidizing preparations

Acidizing safety and environmental protection

Matrix acidizing

PEH:Matrix Acidizing

  1. 1.0 1.1 1.2 1.3 Cite error: Invalid <ref> tag; no text was provided for refs named r1
  2. 2.0 2.1 McLeod, H.O.J. and Coulter, A.W.J. 1969. The Stimulation Treatment Pressure Record—An Overlooked Formation Evaluation Tool. J Pet Technol 21 (8): 952–960. SPE-2287-PA. http://dx.doi.org/10.2118/2287-PA.
  3. 3.0 3.1 Paccaloni, G., Tambini, M., and Galoppini, M. 1988. Key Factors for Enhanced Results of Matrix Stimulation Treatments. Presented at the SPE Formation Damage Control Symposium, Bakersfield, California, 8-9 February 1988. SPE-17154-MS. http://dx.doi.org/10.2118/17154-MS.
  4. Prouvost, L.P. and Economides, M.J. 1989. Applications of Real-Time Matrix-Acidizing Evaluation Method. SPE Prod Eng 4 (4): 401–407. http://dx.doi.org/10.2118/17156-PA.
  5. Economides, M.J. and Nolte, K.G. 2000. Reservoir Stimulation, 20-4–20-8, third edition. West Sussex, England: John Wiley and Sons, Ltd.
  6. McLeod, H.O.J. 1984. Matrix Acidizing. J Pet Technol 36 (12): 2055–2069. SPE-13752-PA. http://dx.doi.org/10.2118/13752-PA.
  7. Hill, A.D. and Zhu, D. 1996. Real-Time Monitoring of Matrix Acidizing Including the Effects of Diverting Agents. SPE Prod & Oper 11 (2): 95-101. SPE-28548-PA. http://dx.doi.org/10.2118/28548-PA.
  8. Montgomery, C.T., Jan, Y.-M., and Niemeyer, B.L. 1995. Development of a Matrix-Acidizing Stimulation Treatment Evaluation and Recording System. SPE Prod & Oper 10 (4): 219-224. SPE-26579-PA. http://dx.doi.org/10.2118/26579-PA.
  9. D. Zhu, Hill, A.D., and Morgenthaler, L.N. 1999. Assessment of Matrix Acidizing Treatment Responses in Gulf of Mexico Wells. Presented at the SPE Mid-Continent Operations Symposium, Oklahoma City, Oklahoma, 28-31 March 1999. SPE-52166-MS. http://dx.doi.org/10.2118/52166-MS.
  10. Hill, A.D. and Zhu, D. 1996. Real-Time Monitoring of Matrix Acidizing Including the Effects of Diverting Agents. SPE Prod & Oper 11 (2): 95-101. SPE-28548-PA. http://dx.doi.org/10.2118/28548-PA.
  11. Ali, S.A. et al. 1997. Process Optimized Acidizing Reduces Production Facility Upsets. Oil & Gas J. 95 (6): 44.
  12. Ali, S.A., Durham, D.K., and Elphingstone, E.A. 1994. Testing Identifies Acidizing Fluid/Crude Compatibility Problems. Oil & Gas J. 92 (13): 47.
  13. Bansal, K.M. 1993. Effect of Nonproduced Fluids on Produced Water Treatment Equipment Efficiency. Presented at the SPE International Symposium on Oilfield Chemistry, New Orleans, Louisiana, 2-5 March 1993. SPE-25199-MS. http://dx.doi.org/10.2118/25199-MS.
  14. Al-Dahlan, M.N. and Nasr-El-Din, H.A. 2000. A New Technique to Evaluate Matrix Acid Treatments in Carbonate Reservoirs. Presented at the SPE International Symposium on Formation Damage Control, Lafayette, Louisiana, 23-24 February 2000. SPE-58714-MS. http://dx.doi.org/10.2118/58714-MS.
  15. Gdanski, R.D. and Shuchart, C.E. 1998. Advanced Sandstone-Acidizing Designs With Improved Radial Models. SPE Prod & Fac 13 (4): 272–278. SPE-52397-PA. http://dx.doi.org/10.2118/52397-PA.