New Structural Evolution Model for the North Kuwait Carbonate Fields and its Implication for Fracture Characterisation and Modelling
Authors: Richard Pascal , Bazalgette Loic , Kidambi Vijaya Kumar , Laiq Kamran , Odreman Allan , Al Qadeeri Bashar , Narhari Rao , Pattnaik Chinmaya , Al Ateeqi Khalid 
Published: March 2015

This paper presents a new structural model for the North Kuwait Carbonate fields as well as its implications in term of fracture modelling and field development. It also describes a workflow which can be used as foundation for further fracture modelling study at production and exploration scales alike. This workflow consists of a four step approach: elaboration of a regional structural model,creation of 3D conceptual fracture diagrams,elaboration of constraints capturing the key elements of the conceptual diagrams andcreation of fracture model properties for further dynamic simulation.

The application of this workflow resulted in the creation of a series of fracture models for the North Kuwait Carbonates fields. During the first step of the study, a new structural model has been elaborated based on key kinematic observations from well and seismic data, as well as experimental and field analogues which have been linked to the known regional phases of deformation. These main phases of deformation are 1) post Triassic rifting, 2) Alpine 1 - late Cretaceous transtension and 3) Alpine 2 - Mid Tertiary compression related to the Zagros formation, which has the greatest impact on the formation of the pre-Gotnia structures and fracture development. The major difference between the new model and previous structural thinking is that the formation of the compressional folds in the Carbonate fields (an event that shaped the current outline of the fields) has happened during the Tertiary time instead of Jurassic time. The proposed structural evolution has been used to define characteristic structural domains. These structural domains have defined a foundation to elaborate conceptual fracture diagram to support fracture modelling study work. The fracture conceptual models have potential implications on fracture development and preferred direction of horizontal and deviated wells. Greater fracture connectivity is expected in compressional ridges developed in Tertiary time, while in the area between the compressional ridges, less dense fractures and probably more cemented fractures (likely to have developed before hydrocarbon emplacement) are expected. The new view on the timing of the structural development (i.e., late uplift of compressional ridges regionally) also has possible implications on maturation/charge history as well as reservoir properties development.

The new proposed model for structural evolution is now being used as a foundation for appraisal and fracture modelling activities of the pre-Gotnia carbonate reservoirs. A fracture characterisation study integrating all available static and dynamic data is ongoing.

Introduction

Kuwait Oil Company (KOC) is currently engaged in aggressively developing the challenging tight carbonate reservoirs (Figure 1) of North Kuwait spread over an area of approximately 1700 sq.km. A paradigm shift in field development process was adopted for tackling these hitherto less developed plays. These North Kuwait reservoirs are characterized by low porosity (average &lt; 5pu), low permeability (average &lt;0.1mD) and occur in deep (&gt; 13500ft depth), HP/HT (average 11000psi/280°F) sour conditions. Though dolomitization improves reservoir characteristics in parts of the area, natural fractures play a dominant role in aiding production from these reservoirs. Hydrocarbon fluids in these reservoirs range from near critical gas-condensate to volatile oil. A detailed interpretation and integration of log, core, and seismic data helped in refining the depositional model. Due to the early life cycle stage of these fields, concurrent appraisal and development of all the fields is ongoing, and a phased development plan has been adopted by KOC as the appropriate development strategy. This allowed KOC to focus on the initial objectives of early assessment of potential in Phase I and to integrate the learning's from Phase I in to the subsequent development phases. The plan generated a strong technical case supporting the business decision to implement Phase II of the development. Currently wells are producing to an early production facility but the desired production capacity (Phase II) requires a large number of new wells to be drilled including horizontal wells.