This paper presents the calcareous nannofossil zonation of the Middle and Upper Jurassic of onshore Kuwait and formalizes current stratigraphic nomenclature. It also interprets the positions of the Jurassic Arabian Plate maximum flooding surfaces (MFS J10 to J110 of Sharland et al., 2001) and sequence boundaries in Kuwait, and correlates them to those in central Saudi Arabia outcrops. This study integrates data from about 400 core samples from 11 wells representing a nearly complete Middle to Upper Jurassic stratigraphic succession. Forty-two nannofossil species were identified using optical microscope techniques. The assemblage contains Tethyan nannofossil markers, which allow application of the Jurassic Tethyan nannofossil biozones. Six zones and five subzones, ranging in age from Middle Aalenian to Kimmeridgian, are established using first and last occurrence events of diagnostic calcareous nannofossil species. A chronostratigraphy of the studied formations is presented, using the revised formal stratigraphic nomenclature. The Marrat Formation is barren of nannofossils. Based on previous studies it is dated as Late Sinemurian–Early Aalenian and contains Middle Toarcian MFS J10. The overlying Dhruma Formation is Middle or Late Aalenian (Zone NJT 8c) or older, to Late Bajocian (Subzone NJT 10a), and contains Lower Bajocian MFS J20. The overlying Sargelu Formation consists of the Late Bajocian (Subzone NJT 10b) Sargelu-Dhruma Transition, and mostly barren Sargelu Limestone in which we place Lower Bathonian MFS J30 near its base. The lower part of the overlying Najmah Formation consists of the Najmah Shale, which is subdivided into three subunits: (1) barren Najmah-Sargelu Transition, (2) Late Bathonian to Middle Callovian (lower Zone NJT 12) Lower Najmah Shale, and (3) Middle Callovian to Middle Oxfordian (upper Zone NJT 12 to NJT 13b) Upper Najmah Shale. Middle Callovian MFS J40 and Middle Oxfordian MFS J50 are positioned near the base and top of the Upper Najmah Shale. The upper part of the Najmah Formation is represented by the Late Oxfordian (Subzone NJT 13b) Najmah Limestone, and is overlain by the Kimmeridgian (Zone NJT 14) Jubaila Formation. Early Kimmeridgian MFS J60 and Late Kimmeridgian MFS J70 are positioned near the base and top of the Jubaila Formation. The positions of Late Jurassic MFS J80, J90 and J100 are not constrained by our biostratigraphic data and are positioned in the Gotnia Formation. The Upper Tithonian MFS J110 and the Jurassic/Cretaceous boundary are positioned in the Makhul Formation.

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Exploration activity during the last eight years, targeting Jurassic carbonate reservoirs in North Kuwait, has culminated in the discovery of six major tight gas fields, encompassing an area of about 1,800 sq km with a reservoir gross thickness of about 2,200 ft. These fields are the first free-gas fields in Kuwait, which were put on early production during 2008. The reservoirs are characterized by dual porosity, dominated by low porosity and permeability, in deep HP/HT conditions, with wide variety of hydrocarbon fluids ranging from black oil to gas condensate with sour gas. Typical per well production rates are up to 5,000 BOPD/BCPD and 10 MMSCFPD, making them an excellent commercial success. Despite the limited number of 38 well penetrations to date in this large Jurassic complex, understanding of the depositional model has improved over time through careful integration and detailed interpretation of log, core, and seismic data. Based on these studies, a depositional model incorporating sabkha, tidal flats, lagoon, backshoal, shoal, shoreface inner shelf, outer shelf, and slope/basin depositional environments has been built. Hypersaline brines were generated in the lagoon and seeped downward, selectively dolomitizing the underlying strata, creating secondary porosity and permeability, and significantly improving the reservoir characteristics in some of these fields. From the early phases of exploration, the role of natural fractures in enhancing the production from these reservoirs was recognized. Accordingly, well data acquisition is designed to maximize reservoir understanding. Delineation and development well placement are optimized to penetrate the most heavily fractured corridors, through a combination of seismic attributes and Discrete Fracture Network modeling, constrained by available well data.