Reservoir Characterization And 3D Static Model In Tight Carbonate, Open Up Reserves, Tuba Reservoir Sabiriyah Field, North Kuwait
Authors: El-Aziz Sabry Abd , Bryant William , Vemparala Chintamani , Al-Rasheedi Saleh 
Published: May 2016

The Sabiriyah Tuba Reservoir has significant hydrocarbon resources in place with a high degree of reservoir rock and fluid heterogeneity. Until recently, it received marginal development attention, and was considered one of the ‘Minor Reservoirs’ of North Kuwait with limited opportunity for production enhancement. Improved reservoir Characterization and the development of a 3D Static model, together with Horizontal Completion technology have now opened up new opportunities for an accelerated development strategy.

The Tuba formation represents a carbonate ramp with different lithofacies association from more proximal depositional setting to more distal environments. Even though the northern area of the field is represented by deeper facies, the reservoir quality shows comparable porosity and permeability trends. The porous and permeable aggradational and progradational carbonate of Upper & Lower Tuba respectively, constitute the main oil accumulations where reservoir quality is strongly controlled by structure, primary depositional fabrics, as well as extensive dissolution process.

It has a significant vertical and horizontal variation in oil quality ranging from low 11–18 API oils to better quality 23 API oils. Current performance of the producer wells indicates that Tuba has the potential to enhance dry oil production.

Tuba reservoir is divided into 3 main stratigraphic units, Upper, Middle & Lower and each unit is further subdivided into sub-layers. The geological layering based on sequence stratigraphy combined with 3D seismic data provided the framework for structural model. The high resolution model was achieved by generating 3D faulted grids and integrating all the components such as all the deterministic structure maps and petrophysical results in to one geo-cellular model applying different approaches and techniques. The model and visualization proved valuable in the interpretation of the primary depositional and secondary digenetic processes that left their imprints on Tuba rocks

The study helped accelerate the development of the Tuba reservoir, and led to new Drilling & Workover opportunities that converted to &gt;500% increase in Oil production. Additionally, from this study, an estimated increase in recoverable reserves of &gt;60% would now support a long term development plan and reserves growth for North Kuwait.

Introduction

The Sabiriyah Tuba Reservoir is an Upper Cretaceous (Cenomanian) age belongs to the category of Minor Reservoir" in Sabiriyah field, North Kuwait (Fig-1). The Tuba reservoir is a part of North Kuwait resources and attempts were made to fully understand and develop the reservoir. Tuba with other minors reservoirs are expected to contribute significantly to the North Kuwait production target.

The tuba formation is a carbonate reservoir interpreted as a highstand and transgresive system which comprises dominantly skeletal mudstone, wackstones, packstones and rare grainstone / floatstone that can be rationalized into six facies associations (lagoonal, inner ramp, shallow mid ramp, deep mid ramp, outer ramp & offshore).Tuba was originally divided into 3 major startighraphic units (Lower, Middle & Upper). The sequence stratigraphy and reservoir layering scheme was carried forward from integrated open well log data supported by 8 wells with core data. These wells are centered to the north and one well in southern area of the Sabiriyah structure.