Introduction The Sabiriyah Tuba Reservoir is an Upper Cretaceous Carbonate reservoir overlying the Mauddud Formation. The Tuba reservoir is a limestone member of Ahmadi Formation and is sandwiched between underlying Wara shale at the bottom and overlying Ahmadi shale at the top. It has been penetrated by all deep wells in Sabiriyah as well in surrounding Raudhatain and Bahrah structures. Together with other "Minor Reservoirs" they represent a significant component of the North Kuwait Development Plan, and are scheduled for full development. The OIP is uncertain. However recent mapping shows that the Tuba reservoir footprint is similar in area to that of Sabiriyah Mauddud suggesting 1100 mmbbl STOIIP. Although it has been penetrated by more than 260 wells, it has been tested in only four. Tuba is currently producing only from one well @500 b/d from a reservoir layer. Based on well log signature and core analysis, the vertical distribution and relative stacking of lithofacies associations within the Tuba Reservoir has lead to the identification of a clear Lower, Middle and Upper reservoir units/subdivisions of Tuba. This tripartite scheme provides a large-scale sequence stratigraphical framework within which a highresolution zonation is constructed, from which field-wide reservoir architecture is predicted. The Lower Tuba (reservoir zones TL10 to TL60) forms a highstand systems tract of predominantly shallow mid to outer ramp lithofacies associations organized into a series of progradational parasequences. These culminate at the top of the succession with high quality rudist dominated shallow mid-ramp lithofacies. The Middle Tuba (reservoir zones TM10 to TM30) comprises a transgressive systems tract that is made up of the outer ramp to offshore/basinal lithofacies associations. This reservoir interval could be considered as a potential field-wide non-reservoir succession and is likely to act as a key transmissibility barrier between hydrocarbon bearing zones at the top of the Lower Tuba. The Upper Tuba (reservoir zones TU10-TU90) comprises a basal highstand systems tract and an upper transgressive systems tract, both of which are dominated by deep mid to outer ramp, and offshore/basinal lithofacies associations. Thus, suggesting deposition of Tuba in carbonate ramp setting. Finally, these outcomes is considered in terms of sequence stratigraphy, which interprets the depositional stacking exhibited and provides a more predictive framework that will have potential for full-field application, and implications for reservoir architecture, which will assess how the sequence stratigraphy will impact on reservoir architecture and ultimately flow behaviour. Background and Scope Tuba reservoir is an upcoming reservoir of Sabiriyah Field, North Kuwait. Most of the wells drilled on the structure have penetrated Tuba but only four wells have been tested in this reservoir, out of which only one well is on production at present. The activities in Tuba so far have been confined mainly to the northern part of the field with cores, only in seven wells, falling in this part. The study of cores from seven wells was carried out by Badley-Ashton in 1999 that provided significant information about the reservoir. The data acquired from additional wells drilled were studied which when coupled with earlier findings has provided an insight and useful information for Tuba reservoir in Sabiriyah Field.

The Mauddud carbonate, a ‘Major' reservoir in Sabiriyah field, North Kuwait, is about 400 feet thick dominated by carbonates deposited in a ramp environment. The reservoir has ten sub-zones named alphabetically from top MaA to MaJ. Current drilling campaign is being executed on fast track exclusively using Non-Conventional Wells (NCW) in order to achieve production targets. The planned NCWs are located in flank areas to have optimum exploitation of flank potential. ‘MaB' is target zone as water flood development of the reservoir, as a whole, calls for enhancing the production from MaB and provide the pressure support via water injection at the MAE (Bottom-up approach). The laterals planned are in the range of three to five thousand feet. Several subsurface challenges were dealt with during design and execution phases. The trajectories are planned with strike parallel azimuths to have minimum inclination changes in lateral sections. The objective is to enable trouble-free operation during ICD deployment. This task was extremely difficult due to local dip changes and variations of actual strike directions. Structure models were constantly updated with real time data and gradual azimuthal shifts were made to achieve this objective. The wellbore must remain in "sweet spot?? throughout. Geological models were used to design trajectories accordingly. This mission was arduous due to sparse well density thereby reducing reliance on models. Presence of sub-seismic faults could place wellbore in undesired stratigraphic positions. Such occurrences were perceived and predicted as best as possible based on regional structural picture and calculated steps were taken. In the eventuality of wellbore hitting unexpected faults, gradual azimuthal-inclination changes were made to correct well paths. With all these efforts and strategies, the operations team was able to successfully execute drilling and completion of Sabiriyah Mauddud Horizontal wells. The paper is aimed at sharing the success story achieved in North Kuwait.

Mauddud reservoir in Sabriyah field is a giant heterogeneous carbonate reservoir discovered in 1950s. The field is on production since 1957 with natural depletion since it has no aquifer support. Overtime, with continuous production there has been a decline in reservoir pressure which affected the field productivity. This paper presents successful field development strategies on multi-discipline approach, integrating sub-surface domains through comprehensive planning studies and high end geo-steering technologies with objective to arrest the pressure decline and sustain oil productivity from the Sabriyah Mauddud giant carbonate reservoir. For optimum exploitation of giant Sabriyah Mauddud reservoir, KOC is currently performing high volume producer and injector horizontal wells drilling campaign. Meticulous predrill planning integrated with advance geo-steering technologies such as Multiple Bed Mapping Distance to Boundary (DTB), Azimuthal Density and Ultra High Resolution Resistivity Image helped KOC to get best results from horizontal wells, not only in short term, but more importantly long term. An effective horizontal well would minimize amount of attic oil, delay water production and hence increase ultimate reservoir recovery. To reduce overall well cost, minimize well bore instability and maximize well production, a very innovative strategy was adopted to drill medium radius 8.5" curve sections with high dog leg severity using special drilling technologies. The Mauddud reservoir varies in property and thickness in different segments of the field, therefore tailored-to-fit drainholes strategies were adopted to exploit the massive Sabriyah carbonate reservoir efficiently. The new strategy of high dog leg medium radius ensured footage reduction by almost 50% in build section. Lower inclination through top shale sections ensured better wellbore stability and smoother drainhole. Reduction in footage meant the curve sections were drilled in less than 48 hours in a single run and resulted in huge cost savings. Another major achievement of this strategy was that landing point was positioned closer to mother bore (for sidetrack) because of reduced horizontal displacement by approx. 60%. After implementing drainhole strategies tailored to address unique challenges of particular segment of the field, horizontal producer and injector wells were successfully placed on top and bottom part respectively of Mauddud reservoir with desired exposure length, resulting in maximum reservoir contact and minimize water coning. An overall improvement of 30% in production rate and maintained water cut rate recorded on applied horizontal well case studies compared to non-horizontal wells. Consistent application on these field development strategies would be beneficial in long term by achieving increase of ultimate field recovery. This paper provides insight on successful application of innovative field development strategies to optimize production from Sabriyah Mauddud reservoir. Field specific development plans along with innovative landing strategy and proactive geo-steering with multi boundary mapping along with high resolution resistivity imaging tools minimize geological risk and helped to achieve horizontal well and field development plan objectives. Similar approach can be adopted to sustain long term oil productivity from this type of complex carbonate reservoir.

By using Persistent and Daily Digital Oil Field Diagnostics techniques a KOC FD team transformed a 5 year closed well, into a 2000 mdb Oil Gain with a remarkable 0% water cut also been achieved. Historically wells completed in Complex & heterogeneous carbonate reservoirs always surprised the NOC NK FD team with distinctive behavior and anomalies, noting also that the NOC's North Kuwait field is on the threshold of embarking upon a strategic ambitious water flood expansion and a systematic increase in injection volumes. Within this process of increasing WI volumes the team realized that it is essential that producing wells are continuously analyzed with the latest Digital Field dynamic data and tangible decisions are made to manage the Voidage-Replacement Ratio. It was during this review process that Well-M was recognized to have a potential added value opportunity This paper outlines both DOF technical review and management process's used in transforming what was seen as a DEAD and closed well into a daily valuable contributor to the NK asset and assist KOC meeting its production goals. The paper closes in lessons learned and the next steps to embed this process into KOC's management processes.

Because core porosity versus permeability relationships are often limited for predicting production performance, it is desirable to investigate alternative methodologies to improve permeability estimates. This paper presents a workflow using logging-while-drilling (LWD) sensor measurements, namely laterolog resistivities for permeability derivation and high-resolution microresistivity images for porosity partitioning. High-resolution microresistivity images were used for traditional picks of symmetric features, such as bedding planes and fractures, as well as for identification of asymmetric features, such as vugs or secondary porosity. The estimation of secondary porosity was based on several assumptions. In water water-based mud (WBM) systems, the encountered vugs during drilling will be filled with conductive fluid and hence display dark pixels on the high-resolution image. The determination of these features was based on a histogram of pixels created corresponding to a full azimuthal coverage. Next, an associated mean value and standard deviation were calculated, and any pixel values lower than the average minus a standard deviation was classified as a vug. The number of these pixels was then divided by the total count of all pixels, the fractional value of which then represented the ratio of secondary porosity with respect to total porosity. This ratio could then be converted into porosity units (pu) from any independent source. Permeability transform was based on the average image resistivity and/or conductivity values from button values, which were then normalized to an external permeability value or indicators; in this paper, these were formation tester mobility measurements. The workflow also entailed partitioning of the horizontal section to different intervals based on the derived permeability profiles and petrophysical attributes. Finally, the derived results from microresistivity and mobility measurements were analyzed to provide qualitative estimates of permeability, leading to identification of reservoir flow units. This paper presents a case study where the discussed methodology was applied and provided the derived interpreted results. Multiwell interpretation in this reservoir sector in the vicinity of the case study well, together with further data integration, is desirable to fine-tune this methodology and workflow.