Petrophysical Evaluation Challenges in Shallow Gas Reservoir Deposited in Sabkha Environment, Case Study, UAE

Abstract

The petrophysical evaluation for Sabkha environment is very challenge due to high reservoir heterogeneity and complex mineralogy in addition to existing of multi-lamination that have various thickness ranging from 1 to 20 ft., also these kinds of reservoirs normally have very high formation salinity that impact as well the water saturation calculations. In 2018, a unique worldwide biogenic shallow gas reservoir was discovered in Onshore Abu Dhabi, UAE in Miocene Sabkha deposits while drilling a dedicated well for deeper reservoir, the average reservoir gross thickness is about 4500 ft. with hundreds of intercalations from Clay, Limestone, Dolomite, Marl, Anhydrite and Halite. This paper presents the detailed challenges for such reservoir regarding the petrophysical evaluation (including but not limited to porosity calculations, water saturation evaluation by different methodology, net to gross ratio, log and core data integration, definition of high potential spot for testing, etc..) Moreover, the way to manage and mitigate these challenges in addition to testing technology and results. So far Five dedicated exploration wells were drilled in this reservoir at which a complete set of logs were acquired in addition to collecting of core footage about 4560 ft. from two wells and analysis is ongoing, also Rigless testing was done for 3 wells. In general, based on collecting data the reservoir properties showed very tight reservoir (permeability < 0.01 md) with high mineralogy complexity as well as high formation salinity (+ 300 kppm). Good Total Organic Carbone is also measures across the reservoir that confirmed the ability to produce Microbial gas. As a results of the integrated study, the sweet spots across the reservoir were identified and tested, accordingly placement for horizontal development wells as well as stimulation technology are optimized