Applications of Geophysics to the Al Shaheen Field, Qatar, for Reservoir Characterisation and Field Development
Authors: Lorenzen R. , Madsen L. , Huegen C. , Ting T. , Henderson J. R. , Raborn C. B. , Uldall A. , Cromie H. , Zampetti V. , Emang M. I. 
Published: May 2016

A comprehensive seismic interpretation programme was recently initiated with the purpose of further increasing the use of 3D seismic data for reservoir characterisation and field development in the Al Shaheen Field, offshore Qatar. Reprocessing of existing seismic data was part of the programme to ensure best data quality for the interpretation. The Al Shaheen Field is a layered carbonate dominated field with multiple reservoirs at different stages of development. Reservoir characterisation is a key driver for both new development areas in the field and for optimisation of existing development areas. Geological topics relevant to reservoir characterisation and field development where seismic data support the reservoir models include faults, reservoir architecture and properties. In this study we present results of integrated seismic interpretations aiming at improving the reservoir characterisation. The results span three of the important reservoirs: Kharaib, Shuaiba, and Mauddud. Through seismic interpretation and integration with geological data and concepts, a consistent field-wide fault framework has been defined. A complex channel system in the Shuaiba reservoir and clinoforms in Mauddud have been mapped. The porosity distribution in the Kharaib reservoir has been estimated using seismic attributes. Additionally all the main geological surfaces defining the general structure and stratigraphy have been mapped. For some results the confidence is high and they can be used directly in the reservoir characterisation and building of static and dynamic models. Other results are less certain e.g. porosity of the Kharaib reservoir. Where this is the case, the results are used to help define uncertainty ranges for the models, as well as enabling testing of different scenarios in the modelling. Properly integrated with all available field data, the value of seismic data is to help create a spatial understanding of geological features that cannot be achieved from well data alone.

Introduction

The giant Al Shaheen Field in Block 5 and 5 Extension (Figure 1), located offshore Qatar, is producing from a series of stacked reservoirs, comprising mostly carbonates but also clastics of Barremian to Cenomanian age. The reservoirs have varying geological characteristics from homogeneous (uniformly layered, laterally continuous) to heterogeneous (complex internal architecture and facies distribution with substantial diagenetic overprint). Common features of the reservoirs are that they are laterally extensive, have low, though laterally variable, oil viscosity, and low reservoir energy.

Development drilling began in 1994 in the Kharaib, Shuaiba and Nahr Umr reservoirs. As the reservoirs are relatively shallow, thin and tight the field was developed with long horizontal wells from the beginning. The development concept has been especially successful in the Kharaib due to the simple, uniformly layered internal stratigraphy which gave optimal conditions for effective well placement through geo-steering. The concept also worked well in the thin sands of the Nahr Umr. At that time only 2D seismic was available in Block 5.