In tight Cretaceous carbonates with complex reservoir and fluid typing, Nuclear Magnetic Resonance (NMR) petrophysical solutions has become a one of the integral logging technology to provide reliable and robust solution through systematic acquisition and processing methodology. This paper covers a case study from two carbonate fields of UAE applying innovative NMR log analysis techniques to understand varying complex reservoir porosities, permeabilities, identifying irreducible water, movable hydrocarbon and water in complex tectonic-cum-geological area, and identifying difficult gas-condensate fluid regime, validated by fluid sampling and testing to support optimizing well placement, and bringing confidence for fast track appraisal-cum-development program.
The Nuclear Magnetic Resonance (NMR) Logs and its derivatives bring lots of value addition to overcome challenges in reservoir and fluid characterization for tight, complex and heterogeneous carbonate reservoirs. In the early life of exploration and fast appraisal stage of any carbonate field, measuring NMR log data for porosity typing (clay, capillary & free fluid), permeability variations, irreducible water saturation, identifying presence of movable water in unknown fluid contacts and resolving hydrocarbon typing through continuous T1T2 (simultaneous longitudinal relaxation-T1 & transverse relaxation-T2) with two dimensional (2D) fluid characterization to assist in differentiating condensate, gas, and water in reservoir static condition are such useful technical information coming out-off single logging tool to properly access reservoir and field potential. NMR data like porosity, rock matrix density and irreducible water saturation continuous profiling is already filling the gap for routine core analysis and capillary pressure data. These outputs from NMR can be easily integrated with other logs and geoscience data to plan perforation and testing in such challenging reservoirs. Despite NMR having shallower depth of investigation, with proper log acquisition plan, a good NMR data can be acquired and interpreted to get reliable interpretations for rock and fluid characterization, overcoming borehole and its fluid influences. Further all these NMR valuable data can be used for the application of reservoir rock typing in such complex carbonate reservoirs, if required. In today’s lower oil price and cost optimization phase, NMR logging is becoming popular acquisition tool providing most of time efficient petrophysical answers to reservoir and fluid characterization.
The NMR log analysis products namely porosities (clay, capillary & free fluid), permeability, irreducible water, and fluid typing in difficult gas-condensate fluid regime validated by fluid sampling and testing has helped in trusting this systematic approach for fast track appraisal-cum-development program in these exploration-cum-fast appraisal carbonate fields.
The NMR based log evaluation has been integrated with other logs and geoscience data to bring clarity on reservoir characterization, fluid typing and fluid contact to update the static model accordingly.