Unlocking the True Potential of Low Permeability Hydrocarbon Zones in a Lower Cretaceous Reservoir
Authors: Mohamed Ramy Abdelkader , Osman Haytham , Zeybek Murat , Mattar Tariq , Majumdar Kuntal , Ebrahim Abdullah 
Published: June 2015

There is a considerable volume of hydrocarbon located in challenging carbonate reservoirs around the world. These reservoirs can be difficult to evaluate with conventional logging measurements and therefore the hydrocarbon reserves can be underestimated.

On the other hand, as the recent development has focused more on low to ultra-low carbonate permeability zones, the testing program becomes very difficult, and getting fluid samples to determine the properties becomes a challenge.

A thin Lower Cretaceous carbonate reservoir with relatively low permeability is undergoing development by drilling maximum reservoir contact wells. Reservoir characterization on three recently drilled wells in this carbonate reservoir reveals a gas cap, and a long oil-water transitional zone complicated by capillary pressure effect, which made it difficult to determine fluid contacts by using pressure gradient. To overcome these issues, a new approach has been used in these three wells, by utilizing a new wireline formation testing tool, scanning across transition zone for direct mobile fluid identification, along with a full suite of petrophysical evaluation data, which resulted in considerable time saving and provided a better estimate of an oil-water contact (OWC). This leads to a big improvement in the estimation of hydrocarbon volumes, and efficient completion design. The preference of new technology measurements over conventional and standard logging facilitated in better determination of the hydrocarbon properties in situ, which goes a long way in understanding the present condition of the reservoir, thereby helping in the planning process of the development of the same.

In this paper, cases will be presented to demonstrate how the modern logging techniques helped in extending the hydrocarbon zone; therefore, more hydrocarbon can be claimed, while providing a unique solution of testing these formations as well as predicting the possible production capability

Introduction

This work was a part of a study to identify fluid contacts in a carbonate reservoir. This field is characterized by good porosity, moderate to low permeability and long transition zones.

The reservoir is heterogeneous in lithology due to the development of rudist banks, syn-depositional faulting and later digenetic overprinting. Sequences within the buildup are difficult to map, probably because of growth faulting, depositional topography, rapid facies changes and stacking and shingling of rudist banks.

The producing formation in the field was developed for oil and gas, and a facies map and a reservoir model were generated. Subsequently, the descriptive framework was done by using logs and available pressure and sampling data. By integrating this framework with a geological model, better planning and geosteering of horizontal wells could be accomplished. This case study will help in characterizing the field, and therefore lead to better simulation models.