Development of Acid Fracturing Model for Naturally Fractured Reservoirs
- Assiya Ugursal (Texas A&M University) | Ding Zhu (Texas A&M University) | Alfred Daniel Hill (Texas A&M University)
- Document ID
- Society of Petroleum Engineers
- SPE Production & Operations
- Publication Date
- November 2019
- Document Type
- Journal Paper
- 735 - 748
- 2019.Society of Petroleum Engineers
- natural fracture network, acid fracturing
- 3 in the last 30 days
- 276 since 2007
- Show more detail
- View rights & permissions
|SPE Member Price:||USD 5.00|
|SPE Non-Member Price:||USD 35.00|
During an acid fracturing treatment in a carbonate reservoir, acid is injected into the formation, thus creating hydraulic fractures and opening existing natural fractures. As the acid flows into natural fractures that intersect hydraulic fractures (main fractures), it etches the walls of the natural fractures, which then increases the natural fractures’ width and generates conductivity. On the other hand, because of the increased acid leakoff into natural fractures, the acid volume in the main fracture decreases, resulting in less conductivity for the main fracture. Existing acid fracturing models estimate the fracture conductivity by assuming that the acid flows and reacts in the hydraulic fractures only. To accurately predict the performance of acid fracturing in naturally fractured carbonate reservoirs, the acid etching of natural fractures should be taken into account when calculating the overall fracture conductivity.
A model was developed to predict the acid fracturing performance in naturally fractured reservoirs. The model assumed that the main fracture was intersected by transverse symmetric natural fractures. The model simulated the acid transport, acid/rock reaction, fracture width increase resulting from etching of the fracture walls, and acid leakoff through natural fractures. The model also assumed that the flow (into natural fractures) and the leakoff were pressure-dependent and were changing with time. The conductivity calculation was based on the previously developed correlation that accounts for the heterogeneous nature of carbonate rock.
The effect of the natural fractures’ geometry on leakoff and created fracture conductivity was investigated. The results showed that length and dynamic width, as well as the natural-fracture spacing, played a significant role in defining the leakoff rate and the conductivity of the hydraulic fracture and the natural fractures. It was also found that the position of the natural fractures along the hydraulicfracture length affected the etching of the natural fractures and the resultant conductivity.
The aim of the model is to enable better prediction of the acid fracture conductivity for naturally fractured carbonate reservoirs and improve the feasibility of acid fracturing applications for this type of formation.
|File Size||902 KB||Number of Pages||14|
Arangath, R., Hopkins, K. W., Lungershausen, D. et al. 2008. Successful Stimulation of Thick, Naturally-Fractured Carbonates Pay Zones in Kazakhstan. Presented at the SPE International Symposium and Exhibition on Formation Damage Control, Lafayette, Louisiana, 13–15 February. SPE-112419-MS. https://doi.org/10.2118/112419-MS.
Berman, A. S. 1953. Laminar Flow in Channels Between Porous Walls. J Appl Phys 24: 1232. https://doi.org/10.1063/1.1721476.
Deng, J., Mou, J., Hill, A. D. et al. 2012. A New Correlation of Acid-Fracture Conductivity Subject to Closure Stress. SPE Prod & Oper 27 (2): 158–169. SPE-140402-PA. https://doi.org/10.2118/140402-PA.
Dong, C., Zhu, D., and Hill, A. D. 2002b. Modeling of the Acidizing Process in Naturally Fractured Carbonates. SPE J. 7 (4): 400–408. SPE-81816-PA. https://doi.org/10.2118/81816-PA.
Economides, M. J., Hill, A. D., Ehlig-Economides, C. et al. 2013. Petroleum Production Systems, second edition. Upper Saddle River, New Jersey: Prentice Hall.
Hill, A. D., Zhu, D., and Wang, Y. 1995. The Effect of Wormholing on the Fluid Loss Coefficient in Acid Fracturing. SPE Prod & Fac 10 (4): 257–263. SPE-27403-PA. https://doi.org/10.2118/27403-PA.
Hongjie, X. 1994. Prediction of Effective Acid Penetration and Acid Volume for Matrix Acidizing Treatments in Naturally Fractured Carbonates. SPE Prod & Fac 9 (3): 188–194. SPE-25410-PA. https://doi.org/10.2118/25410-PA.
Leal Jauregui, J. A., Malik, A. R., Nunez Garcia, W. et al. 2011. Successful Application of Novel Fiber Laden Self-Diverting Acid System During Fracturing Operations of Naturally Fractured Carbonates in Saudi Arabia. Presented at the SPE Middle East Oil and Gas Show and Conference, Mahama, Bahrain, 25–28 September. SPE-142512-MS. https://doi.org/10.2118/142512-MS.
McCartney, E., Al-Othman, M., Alam, A. et al. 2017. Enhanced Acid Fracturing With Improved Fluid Loss Control and Near Wellbore Diversion Increases Production in Kuwait. Presented at the SPE Annual Technical Conference and Exhibition, San Antonio, Texas, 9–11 October. SPE-187444-MS. https://doi.org/10.2118/187444-MS.
Mou, J., Zhu, D., and Hill, A. D. 2009. Acid-Etched Channels in Heterogeneous Carbonates—A Newly Discovered Mechanism for Creating Acid Fracture Conductivity. Presented at the SPE Hydraulic Fracturing Technology Conference, The Woodlands, Texas, 19–21 January. SPE-119619-MS. https://doi.org/10.2118/119619-MS.
Mou, J., Zhu, D., and Hill, A. D. 2011. New Correlations of Acid-Fracture Conductivity at Low Closure Stress Based on Spatial Distributions of Formation Properties. SPE Prod & Oper 26 (2): 195–202. SPE-131591-PA. https://doi.org/10.2118/131591-PA.
Mou, J., Zhang, S., and Shang, Y. 2012. Acid Leakoff Mechanism in Acid Fracturing of Naturally Fractured Carbonate Oil Reservoirs. Transp Porous Med 91: 573–584. https://doi.org/10.1007/s11242-011-9860-4.
Nelson, R. A. 1985. Geologic Analysis of Naturally Fractured Reservoirs, second edition. Houston, Texas: Gulf Professional Publishing.
Nierode, D. E. and Kruk, K. F. 1973. An Evaluation of Acid Fluid Loss Additives, Retarded Acids, and Acidized Fracture Conductivity. Presented at the Fall Meeting of the Society of Petroleum Engineers of AIME, Las Vegas, Nevada, 30 September–3 October. SPE-4549-MS. https://doi.org/10.2118/4549-MS.
Salimi, S., Ghalambor, A., and Hayer, H. 2014. Insights Into the Process of Effectively Acidizing Naturally Fractured Reservoirs. Presented at the SPE International Symposium and Exhibition on Formation Damage Control, Lafayette, Louisiana, 13–15 February. SPE-168126-MS. https://doi.org/168126-MS.
Schechter, R. S. 1992. Oil Well Stimulation. New Jersey: Prentice Hall.
Ugursal, A. 2018. Development of Acid Fracturing Model for Naturally Fractured Reservoirs. PhD dissertation, Texas A&M University, College Station, Texas (August 2018).