Evaluation of organic-rich shale and its cracking mechanism through acidizing attracts much attention as a result of advancements in deep exploration of unconventional reservoirs. In this paper mineral dislodgment and mineral cracking phenomenon were explained by combined experimental methods including atomic force microscopy (AFM), inductively coupled plasma mass spectrometry (ICP-OES), XRD, XRF, Ion chromatography and SEM-EDS to characterize microstructure of individual minerals for pre and post acidizing test samples. Two types of core samples from Longmaxi marine and Yanchang continental shale formations were emphasized for acidizing behaviors by employing hydrochloric acid (15%+ 3%KCL) as the acid fluid medium to treat shale samples for 240 minutes. Moreover, the mechanical mapping was conducted via AFM to identify the variation of mechanical properties of the targeted minerals. Porosity and microfractures were generated due to compression caused by mineral grain displacement mostly on the areas dominated by carbonate minerals for Longmaxi marine formation carbonates and non-swelling clay minerals (Kaolinite, Chlorite), thus contributing in generation of secondary pores. Inter-particle and Intra-particle pores are greatly enchanted as a result of acidizing in carbonate regions of Longmaxi marine shale formation. Yanchang continental shale is mostly dominated by intra-particle pores that effect greatly in the generation of overall porosity enhancement in shale. However Clay mineral swelling was restricted as presence of non-reactive minerals near the clay causes hindrance due to dissolution effect after post acidizing treatment. Secondly during reaction some heavy ions such as iron or potassium may precipitate out and gets deposited on clay minerals. This phenomenon increases the mechanical strength as clay is easily deformed considering its low elasticity and weaker poisson ratio. Acid dissolution cracks are generated as a result of mineral dissolution of carbonate and iron-oxide regions. Acid induced cracks are also generated as a result of mineral grain displacement due to creation of void spaces that are generated due to mineral dissolution. Due to reaction some of the ions get deposited on the shale surface while some ions are dislodged and get immersed in the acid solution. The different ions formed on surface of shale and in the acid solution were closely monitored as these ions are the driving factors for the generation of micro-cracks and porosity enhancement on shale sample. This paper would help to understand the creation of microfractures and pores in a more efficient and detailed way.
Mineral Cracking and Porosity Enhancement of Shale Through Acidizing
- Share Icon Share
- Search Site
Sheng, Mao, Khan, Waleed Ali, Cheng, Shizong, Zhang, Panpan, Tian, Shouceng, and Quan Xu. "Mineral Cracking and Porosity Enhancement of Shale Through Acidizing." Paper presented at the SPE/AAPG/SEG Asia Pacific Unconventional Resources Technology Conference, Brisbane, Australia, November 2019. doi: https://doi.org/10.15530/AP-URTEC-2019-198298
Download citation file: