Effects of Heterogeneity in Mineralogy Distribution on Acid Fracturing Efficiency
- Xiao Jin (Texas A&M University) | Ding Zhu (Texas A&M University) | A. D. Hill (Texas A&M University) | Darren McDuff (Chevron)
- Document ID
- Society of Petroleum Engineers
- SPE Hydraulic Fracturing Technology Conference and Exhibition, 5-7 February, The Woodlands, Texas, USA
- Publication Date
- Document Type
- Conference Paper
- 2019. Society of Petroleum Engineers
- 5.1.5 Geologic Modeling, 4.1.2 Separation and Treating, 2.6 Acidizing, 2 Well completion, 4 Facilities Design, Construction and Operation, 4.1 Processing Systems and Design
- heterogeneity, sustained conductivity, acid fracturing
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Creating sufficient and sustained fracture conductivity contributes directly to the success of acid fracturing treatments. The permeability and mineralogy distributions of formation rocks play significant roles in creating non-uniformly etched surfaces that can withstand high closure stress. Previous studies showed that depending on the properties of formation rock and acidizing conditions (acid selection, formation temperature, injection rate and contact time), a wide range of etching patterns (roughness, uniform, channeling) could be created that can dictate the resultant fracture conductivity. Insoluble minerals and their distribution can completely change the outcomes of acid fracturing treatments. However, most experimental studies use homogeneous rock samples such as Indiana limestones that do not represent the highly-heterogeneous features of carbonate rocks. This work studies the effect of heterogeneity, and more importantly, the distribution of insoluble rock, on acid fracture conductivity.
In this research, we conducted acid fracturing experiments using both homogeneous Indiana limestone samples and heterogeneous carbonate rock samples. The Indiana limestone tests served as a baseline. The highly-heterogeneous carbonate rock samples contain several types of insoluble minerals such as quartz and various types of clays along sealed natural fractures. These minerals are distributed in the form of streaks correlated against the flow direction, or as smaller nodules. After acidizing the rock samples, these minerals acted as pillars that significantly reduced conductivity decline rate at high closure stresses. Both X-ray diffraction (XRD) and X-ray fluorescence (XRF) tests were done to pinpoint the type and location of different minerals on the fracture surfaces. A surface profilometer was also used to correlate conductivity as a function of mineralogy distribution by comparing the surface scans from after the acidizing test to the scans after the conductivity test. Theoretical models considering geostatistical correlation parameters were used to match and understand the experimental results.
Results of this study showed that insoluble minerals with higher mechanical properties were not crushed at high closure stress, resulting in a less steep conductivity decline with increasing closure stress. If the acid etching creates enough conductivity, the rock sample can sustain a higher closure stress with a much lower decline rate compared with Indiana limestone samples. Fracture surfaces with insoluble mineral streaks correlated against the flow direction offer the benefit of being able to maintain conductivity at high closure stress, but not necessarily high initial conductivity. Using a fracture conductivity model with correlation length, we matched the fracture conductivity behavior for the heterogeneous samples. Fracture surfaces with mineral streaks correlated with the flow direction could increase acid fracturing conductivity significantly as compared to the case when the streak is correlated against the flow direction.
The results of the study show that fracture conductivity can be optimized by taking advantage of the distribution of insoluble minerals along the fracture surface and demonstrate the important considerations to make the acid fracturing treatment successful.
|File Size||1 MB||Number of Pages||19|
Al-Momin, A., Zhu, D., and Hill, A.D. 2014. The Effects of Initial Condition of Fracture Surfaces, Acid Spending and Acid Type on Conductivity of Acid Fracture. Paper presented at the Offshore Technology Conference-Asia, Kuala Lumpur, Malaysia. 15. Offshore Technology Conference. DOI: 10.4043/24895-MS.
Antelo, L.F., Zhu, D., and Hill, A.D. 2009. Surface Characterization and Its Effect on Fracture Conductivity in Acid Fracturing. Paper presented at the SPE Hydraulic Fracturing Technology Conference, The Woodlands, Texas. 14. Society of Petroleum Engineers. DOI: 10.2118/119743-MS.
Beg, M.S., Kunak, A.O., Gong, M.. 1996. A Systematic Experimental Study of Acid Fracture Conductivity. Paper presented at the SPE Formation Damage Control Symposium, Lafayette, Louisiana. 10. Society of Petroleum Engineers. DOI: 10.2118/31098-MS.
Gong, M., Lacote, S., and Hill, A.D. 1998. A New Model of Acid Fracure Conductivity Based on Deformation of Surface Asperities. Paper presented at the SPE Formation Damage Control Conference, Lafayette, Louisiana. 15. Society of Petroleum Engineers. DOI: 10.2118/39431-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. Paper presented at the SPE Hydraulic Fracturing Technology Conference, The Woodlands, Texas. 17. Society of Petroleum Engineers. DOI: 10.2118/119619-MS.
Mou, J., Zhu, D., and Hill, A.D. 2010. New Correlations of Acid Fracture Conductivity at Low Closure Stress Based on the Spatial Distributions of Formation Properties. Paper presented at the International Oil and Gas Conference and Exhibition in China, Beijing, China. 12. Society of Petroleum Engineers. DOI: 10.2118/131591-MS.
Neumann, L.F., Sousa, J.L.A.O., Brandao, E.M.. 2012. Acid Fracturing: New Insigths on Acid Etching Patterns from Experimental Investigation. Paper presented at the SPE Hydraulic Fracturing Technology Conference, The Woodlands, Texas, USA. 9. Society of Petroleum Engineers. DOI: 10.2118/152179-MS.
Nierode, D.E. and Kruk, K.F. 1973. An Evaluation of Acid Fluid Loss Additives Retarded Acids, and Acidized Fracture Conductivity. Paper presented at the Fall Meeting of the Society of Petroleum Engineers of AIME, Las Vegas, Nevada. 12. Society of Petroleum Engineers. DOI: 10.2118/4549-MS.
Nieto, C.M., Pournik, M., and Hill, A.D. 2008. The Texture of Acidized Fracture Surfaces: Implications for Acid Fracture Conductivity. SPE Production & Operations 23 (03): 343-352. DOI: 10.2118/102167-PA
Oeth, C., Hill, A.D., Zhu, D.. 2011. Characterization of Small Scale Heterogeneity to Predict Acid Fracture Performance. Paper presented at the SPE Hydraulic Fracturing Technology Conference, The Woodlands, Texas, USA. 17. Society of Petroleum Engineers. DOI: 10.2118/140336-MS.