Evaluation of Porosity and Permeability Vertical Distribution of Rudist Carbonate Build Up Platform Identified by X-ray CT and 3D Modeling, Late Cretaceous Cenomanian in Offshore Abu Dhabi

Abstract

We investigated the method of estimating porosity/permeability using X-ray CT, a non-destructive method. Using X-ray CT, a method of estimating the porosity/permeability is particularly developed in sandstone. However, for the carbonate rocks, the internal structure is complicated due to biological origin. This is difficult to recognize the pore space, therefore a method of estimating the porosity/permeability using X-ray CT has not been studied. This study is based on Yamanaka et al. 2018, which clarifies rudist development in side slab core using X-ray CT and 3D modeling. The study uses X-ray CT to observe the internal structure from the view of development of rudist of the 200 feet section of the Well A in offshore Abu Dhabi, and compares the porosity/permeability obtained from CCA (Conventional core analysis) of the same well and same interval. Based on the 3D modeling of the X-ray CT, two rudist families (Radiolitidae and Ichthyosarcolites) were identified through their morphological characteristics such as inner diameter and shell thickness. A porosity of slab core around 50 feet is about 18% from CCA (Conventional Core Analysis). This slab core is made up of small rudist populations (length and wide size is 15-10mm), inside core confirmed 3D modeling (surface rendering and volume rendering), and calculated porosity is 0.89% from RCM (Reverse Coupling method). It is understood that this difference is dependent on matrix porosity and further investigation in the future is required in order to measure matrix porosity using thin section and micro X-ray CT. With regards to reservoir properties, the porosity is higher in the lower part than the upper part in the core interval. The size of the Radiolitidae could be dependent on the environment and its vertical variation suggests the change of depositional environment. Larger Radiolitidae, which appeared from 80 to 200 feet below the C-T (Cenomanian-Turonian) boundary, suggests a relatively strong wave influence. From a sedimentological point of view, the coarser matrix grain size supports the interpretation of depositional setting. On the other hand, from 30 to 80 feet below C-T boundary, smaller Radiolitidae is dominated. It was assumed that small Radiolitidae could be due to high physical stress under a restricted environment. This study shows the advantage of X-ray CT image in rudist recognition, based on interpretation of depositional environment and understanding the reservoir property. The result of this study suggests the strong correlation between porosity/permeability and depositional environment (accommodation space) inferred from rudist fossil.

Unconventional hydrocarbon resources: geological statistics, petrophysical characterization, and field development strategies

“…With this, the digital rock physics implementation including the understanding of segmented images through pore network modeling and/or implementation of machine learning technology widely aided in understanding and calculating different core sample properties including the porosity, pore structures, and sizes, and permeability, etc. (Blunt et al 2013;Wildenschild and Sheppard 2013;Armstrong et al 2018;Chung et al 2019;Yamanaka et al 2019;Wang et al 2020;Wan et al 2020;Santos et al 2020;Rabbani and Babaei 2019;Sudakov et al 2019;Tembely et al 2021;Alqahtani et al 2020;Yun et al 2020;Karimpouli and Tahmasebi 2019).…”