Evaluating a Complex Low-Resistivity Pay Carbonate Reservoir Onshore Abu Dhabi: From Model to Implementation

Abstract

Early identification of low resistivity pay (LRP) reservoir is vital in assessing its prospect and capability. Productive reservoirs may exhibit low resistivity and consequently, their potential is simply overlooked. Remapping these intervals can have significant production and reserve implications. Traditionally, resistivity logs are used to identify pay intervals due to the resistivity contrast between oil and formation water. However, when pay intervals exhibit low resistivity, such logs return low confidence in defining hydrocarbon potential. Due to the complexity of low resistivity pay (LRP), its cause and proper mitigation should be determined prior to applying a solution. Researchers have identified several reasons responsible for this occurrence; among which are the presence of heterogeneous pore structures specifically micro-porosity, fractures, paramagnetic minerals, and deep conductive mud invasion. Almost all preceding publications assume a technique will work but not the other. However, this is the first time, to our knowledge; an integrated approach is used to develop LRP assessment workflow. We have integrated the information coming from geology (e.g., thin-section, XRD), formation pressure and well tests, NMR, MICP, and dean stark data. The integration successfully identified and remapped the carbonate low resistivity reservoir. This model was validated in an appraisal well on Abu Dhabi mainland, for that an extended data was acquired. Thereafter, the integrated LRP model was compared with the computed water saturation from conventional resistivity tools. The validation was successful in terms of confirming the prognosis. Interpreting the results from the multidisciplinary integrated model confirms a deeper Free Water Level (FWL), hence oil pool extension. Further analysis showed that the causes of LRP in this considered formation was limited to presence of micro-porosity and high saline mud invasion.

Identification Analysis of Fluid Type in the Low Resistivity Zone of Well Z-2 Field "Z", South Sumatera

“…Low resistivity is a natural phenomenon that occurs in a reservoir or in a zone where the resistivity value of rocks in the zone or reservoir has decreased sufficiently in the hydrocarbon zone or has increased resistivity value in the water zone compared to the actual resistivity value so that it is difficult to be able to distinguish fluid content and identify the actual price of water saturation value. Research conducted to be able to indicate the cause of the phenomenon of low resistivity has been widely carried out as in the research of Ashqar et al (2016) Durand et al (2001) conducted research on the effect of pore lining chlorite on petrophysical properties in low resistivity sandstone reservoirs [9][10][11][12][13].…”

Effect of Well Orientation on Oil Recovery from Waterflooding in Shallow Green Reservoirs: A Case Study from Central Africa

“…Figure 5 shows the porosity and permeability distributions of rock types in reservoir. Uchida et al (2015) and Ashqar et al (2016) discussed the factors that should be considered when classifying rock type for reservoir modeling and evaluation [47,48]. It is noted that when classifying different rock types, facies, porosity, and permeability are all considered.…”

Influence of Low-Temperature Hydrothermal Events and Basement Fault System on Low-Resistivity Shale Reservoirs: A Case Study from the Upper Ordovician to Lower Silurian in the Sichuan Basin, SW China

“…Early recognition of low resistivity pay (LRP) (<3 Ω•m) is critical for analyzing its prospects and capabilities [1]. LRP is not confined to specific lithology, which can occur in sandstones, carbonates, and shales associated with a variety of geological events.…”