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Successful Horizontal Well Placement With Limited Data Control in the Deep Toarcian Age Carbonate Reservoir of North Kuwait: A Case Study

Abstract

Kuwait Oil company is currently engaged in an early phase of appraisal and development of deep fractured carbonate reservoirs of Toarcian age (over 14500ft depth, HPHT) in the northern part of Kuwait, as part of the strategy to meet the long term gas production targets. The operational area in northern part of Kuwait encompasses approximately 1800 sq.km covering eight oil & gas fields. The highly over pressured (up to 21 ppg mud weight equivalent) Kimmeridgian - Tithonian age Hith-Gotnia evaporite formations (Anhydrite + Salt alternations) act as the regional top seal. Till date about 100 vertical/deviated wells have been drilled in this play in this area penetrating these diagenetically altered dolomitic reservoirs of Toarcian age. Extensive conventional core and Open Hole log coverage facilitated thorough sedimentological understanding leading to building a robust sequence stratigraphic model. For maximizing the productivity, the first horizontal well was meticulously planned targeting the best reservoir sweet spot in one of the fields of this operational area. Key challenges for well placement in this reservoir include deep and thin zone of interest (about 15000 ft. TVD deep and 10 to 20 ft. thick), limited offset control (nearest offset well 1000 m) and unfavorable reservoir operating conditions (wide pore pressure range 11.2 to 14.2 ppg). Added to this challenging operating envelope, due to drilling complications, the conventional Real-time full suite of logs (especially porosity log) were not available which imposed severe constraints in landing of the well and drain hole placement. As part of mitigation of the well placement challenges, an innovative approach was adopted utilizing tight integration of real time geochemical and drilling data resulting in 100% placement in the target reservoir. Also, due to lack of conventional suite of open hole logs in the drain hole section, Geochemical analysis of cutting samples (XRD/XRF/Pyrolysis) was carried out to characterize the reservoir. A calibrated model was built based on the offset wells Core data (plus CMR data) for distinguishing between porous reservoir sections and the sections impacted by pore throat impairment due to solid hydrocarbons. This integration study assisted in design and application of suitable stimulation recipe leading to substantial increase in Oil and Gas production from the horizontal well.