Optimum Workflow for Accurate Core Porosity and Permeability Measurements in Salt Formations: A First Case Study in UAE For Hydrocarbon Storage in Salt Caverns

Abstract The accurate evaluation of petrophysical properties in salt formations is crucial for underground hydrocarbon storage, as fractures and permeable zones must be avoided to prevent hydrocarbon leakage from caverns. The objective of this study is to conduct a comprehensive core analysis to assess the integrity and functionality of salt caverns for hydrocarbon storage. Routine core analysis serves as the foundation for measuring essential rock properties such as porosity, permeability, grain density, and CT scan. These properties are instrumental in assessing the integrity of cavern storage. This paper presents the first case study in the UAE, detailing a comprehensive core analysis in salt formations and its application in developing salt cavern projects. To achieve the project's objectives, a fully oriented core was extracted, totaling approximately 2,100 feet across 16 core runs, encompassing the entire salt section, including insoluble zones. A comprehensive routine core analysis was conducted to ascertain the petrophysical properties of the salt rock. Detailed petrographic work involved core description, CT scans, thin-section analysis, scanning electron microscopy, and X-ray diffraction to characterize different salt facies and identify structural features. A unique plug drilling technique with specific parameters was implemented to avoid inducing fractures during plug extraction, ensuring the accuracy of core measurements. This innovative approach yielded an excellent correlation between core analysis and well log evaluations, as well as geomechanical analysis from mini-fracture logging. From the 16 coring runs, a 100% core recovery rate was achieved in the main salt section. During the initial core plug tests, unexpectedly high permeability was observed in low-porosity salt rock plugs, despite preliminary CT scans confirming no fractures prior to plug drilling. Further investigation involved dual-energy CT scans to inspect the plugs post-drilling, revealing induced fractures caused by suboptimal drilling parameters. Consequently, a protocol was established for dual CT scanning of plugs before and after drilling to assess fracture integrity and minimize induced fractures. Optimum drilling parameters were then applied, along with oil-based mud for drilling. Core descriptions, thin sections, and scanning electron microscopy revealed saliferous intervals with partial porosity due to insoluble intercalations, confirmed by XRD/XRF analysis. Ultimately, the results were validated against well logging data, leading to the selection of optimal intervals for the leaching operation in salt cavern development for hydrocarbon storage. The innovative technique implemented for drilling plugs effectively mitigates the creation of induced fractures, serving as a potential guideline for future core analysis initiatives in salt formations. Additionally, the use of dual-energy CT scans before and after plug drilling ensures the integrity of the cores, enhancing the overall reliability of petrophysical evaluations in salt rock environments.