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The Deep carbonate reservoirs of North Kuwait are broadly divided into deeper assemblage consisting of diagenitically modified dolomitic layer and shallower fractured-laminated tight limestone and Kerogen units. It is a challenge to establish and quantify the known phenomenon of dynamic changes in the flow path characteristics and properties of the reservoir rocks, as the natural stability condition are altered by production of reservoir fluid. The parameters of the flow path characterization become more uncertain in case of deep HP/HT digenetically altered reservoirs and fractured-tight limestone with laminated kerogen, then similar to the North Kuwait deep reservoirs.In this study an integration of static data such as, borehole image, core and petrophysical evaluation with time lapse dynamic reservoir parameters like production, pressure data from buildup and pressure transient analysis was carried out to understand the flow path characteristic changes. A deterministic approach has been used to characterize the reservoir flow system and to estimate the fracture aperture for each time step. Thus the time dependent alternations in the flow path properties such as reduced fracture aperture and linked causative phenomena have been studied with multiple scenarios.A detailed inventory and analysis of various well intervention operations between the time lapse measurements was carried out to distinguish the natural vs. work over induced causatives of flow path changes. This has assisted proper calibration of fracture properties for the static conditions, dynamic simulation and history matching. This workflow has also optimized the application of appropriate reservoir health checkups and remedial interventions. Cases of two representative wells completed in each of the deep reservoir assemblages are presented as examples to demonstrate the study.

An advanced neutron spectroscopy measurement combining capture and inelastic spectroscopy with state-of-the-art hardware has been used to directly determine total organic content (TOC) and to provide detailed mineralogy characterization in an organic-rich source rock in Kuwait. The advanced spectroscopy measurement provides a direct measurement of TOC, obtained from the difference between the measured total carbon and the inorganic carbon obtained from the rock mineralogy. TOC is an important component of the evaluation of an unconventional reservoir as it is a direct input into the determination of the adsorbed gas volume. Core studies including X-ray fluorescence, dual-range infrared Fourier transform mineralogy evaluation, and coulometry for carbon were conducted to validate the measurement. The log spectroscopy results were compared with core TOC data and to core elemental and mineralogical data. Evaluation of the advanced spectroscopy tool was conducted in parallel with the previous-generation spectroscopy measurement to compare the results. The core TOC and the direct TOC log measurements of the advanced spectroscopy tool compared well. The core-to-log elemental dry weights comparison highlighted that, compared to the previous technology, the advanced measurement provided a more accurate evaluation of several elements (including aluminum, potassium, and magnesium). The core-to-log comparison also demonstrated that the new measurement provided robust answers in a tough logging environment, with an effective correction for the carbon content of oil-base mud and for barite, despite the high barite content in the mud. A particular finding of the chemistry/mineralogy combined core analysis was that a large quantity of sulfur, larger than is typically found in unconventional reservoirs, is associated with the kerogen. For the first time in Kuwait, the application of an advanced spectroscopy technology in a challenging carbonate environment effectively provides a detailed and accurate mineralogical description and a model-independent TOC measurement that were not previously available with conventional spectroscopy logging techniques.

Traditionally, 12.25-in. hole sections in the Jurassic formations were planned to be drilled with mud weight (MW) of 20 ppg and solids content of 45%. The planned drilling would use a rotary assembly from the Hith formation, crossing several zones in which mud losses or gains were likely. The casing would then be set in the thin shale base of the Gotnia formation. A minor inaccuracy in casing setting depth could often lead to well-control issues. Pore pressure drops severely below the shale base and requires a MW of 15 ppg. Passing this shale base can lead to severe losses and potential abandonment of the well. An anhydrite marker is located approximately 50 ft above the shale base. To reduce risk, the operator would normally drill to this marker at a rate of penetration (ROP) of 20-30 ft/hr, then decrease the ROP to 2 ft/hr. While slowly drilling the last part of the section, penetration would be stopped every few feet to circulate bottoms-up to receive samples confirming the shale base; this process requires an additional 24 hours of rig time. After reaching the casing point, the operator would pull out of the hole to pick up logging-while-drilling (LWD) tools to perform a wiping run. This logging, however, is frequently cancelled because of wellbore stability issues, resulting in the loss of important formation-evaluation data across this interval. A new solution has been developed, comprising drilling with a rotary assembly to the final anhydrite marker, then pulling the string out of hole to pick up LWD triple-combo and sonic tools, with a conventional gamma ray sensor placed only 6 ft from the bit. The remaining part of the section would then be drilled at 7-10 ft/hr until the gamma-ray tool detected the shale base, thereby determining the casing depth. In addition, it was planned to re-log the previously drilled interval. This solution prevented the well from potential abandonment and reduced drilling time. It also secured critical formation evaluation data for exploration and future field development. The engineered drilling solution was tried for the first time in these formation sequences within a harsh drilling and logging environment. The option of rotary steerable services with an at-bit GR sensor was not considered because of the high cost.