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Fracture systems play a significant role in production in the case of tight/low porosity complex reservoirs. Exploration well in North Kuwait that targets Middle Marrat formation is met with the challenge of lack of understanding of reservoir compartments in an under-explored field, with minimum offset wells to properly evaluate its potential. A multi-domain approach is proposed with various expertise to tackle the petrophysical and geomechanical aspects of the fracture system governing the carbonate layer, to assess its producibility and its qualification for stimulation through hydraulic fracturing. To address the exploration challenge, a novel comprehensive approach for fracture evaluation was implemented for the first time, starting at the wellbore stage, followed by an extensive analysis far away from the wellbore to evaluate their extent and their possible contribution to the flow, later combined with a geomechanical evaluation of their stress state, to come up with a confident estimation of their producibility and subsequently, a proper completion optimization plan for maximum reservoir exploitation. The robust approach started with deployment of the image logs photorealistic oil-based mud imager with the purpose of capturing the highest resolution prospect of fractures on the borehole wall. The image logs tool provides direct quantification of fracture properties with regard to their density and orientation, and visual qualification of their type, connectedness, and aperture. The 3D Far-Field Sonic technology was then implemented to unveil the ambiguity typically associated with fracture analysis, and provide new insight into the fracture continuity, reaching up to 160ft away from the borehole circumference which is a unique answer product presented for the first time in oil field market. The 3D Far-Field Sonic delivered astonishing results by identifying highly fractured zones and fracture extensions including the true dip and azimuth for each fracture. Geomechanical evaluation was carried out to understand the stress regime, and the relationship between critically stressed fractures with production patterns, and ultimately provide a location and direction to guide enhanced production in future wells. Integrating data from various advanced tools helped identify zones of producing fractures and provided a practical solution for stimulation optimization. The multi-domain expertise addressed the challenge of natural fractures consistency between different measurements and allowed for proper evaluation of critically stressed fractures to understand production mechanisms and depletion behavior, through understanding present-day stress state, fracture geometry, and fracture slip properties. The consistency of the study provided convenient results ensuring proper well planning and future completion strategies.

No abstract

The acquisition of openhole logging data is not always guaranteed because of difficult drilling environments. In such cases, formation evaluation, and thus the completion program, becomes a real challenge. The situation becomes more complex when dealing with unconventional reservoirs with very tight carbonates and organic carbon-rich formations. This paper presents a method to measure the total organic carbon (TOC), which, in this paper, represents the organic carbon in the matrix (kerogen and coal), and to estimate oil saturation in such a challenging environment. A suite of wireline tools (gamma ray (GR), Spectralog, density, neutron, nuclear spectroscopy) was run through 7.625-in. casing to evaluate the formation and to quantify TOC and the oil in the pores. The nuclear spectroscopy tool, which was the master tool, measures the total carbon in the formation. Part of this carbon is attributed to the inorganic matrix (carbonates). Another part is attributed to the organic matter in the matrix (kerogen). The remaining carbon, or excess carbon, is mainly the carbon inside the pores. The process consists of integrating the conventional logging data, spectroscopy data, core data, and some geological constraints to estimate corrected porosity, mineralogy, and TOC in the kerogen-rich intervals. The excess carbon, which is not attributed to the matrix and TOC, is used to estimate oil saturation. Finally, core data are used to validate the analysis results. The presented methodology has been applied to a casedhole well with no openhole data previously acquired due to drilling issues. The primary target of the well, in the deep section, produced water; then, the operator decided to revisit the second target and complete it for testing. It has to be pointed out that over the well-cemented intervals, the results showed a very good matching of the corrected total porosity and the core total porosity. Relying on TOC and saturation analysis results, the operator selected the most promising intervals to be tested. Testing results have shown excellent matching between production results and oil saturation analysis results. TOC and oil saturation quantification using nuclear spectroscopy technology and core data results showed its success in both tight carbonates and organic carbon-rich reservoirs. This method will be a solution to evaluate and complete any wells with no openhole data acquired, and also to evaluate and complete unconventional formations where the conventional methods have shown their limitations.