Challenges in Capturing Reservoir Heterogeneity in a 3D Static Model – A Case Study in Field A, Malay Basin
Authors: Hashim Naqzatul Shima , Oruganti Bhargava Ram , Yeomans Hugh Gordon , Hong Chong Weng , Mudaliar Kokulananda , Goidescu Nicoleta Mihaela , Redzual Nur Zatil Hulwan 
Published: May 2016

Field A is located offshore Peninsular Malaysia. Initially a gas field, it was established as one of the largest oil fields in Malay Basin following the drilling of appraisal wells from 2005–2009. Based on the discovery of oil, a phase 1 Field Development Plan was developed, which focused on oil production from A & B reservoirs in the main blocks of the field. This was accomplished by drilling 10 wells from an EPS (Early Production System). All the wells were drilled, completed and placed on production as per FDP, and a field production profile is currently being developed, which will be utilized for full field development in the near future.

Upon completion of the successful drilling campaign, a new static model was developed, which utilized data available from the various exploration, appraisal and recent development drilling campaigns. Building the static model for this field proved to be a challenging task due to reasons highlighted below:1.Thinly laminated reservoir/non-reservoir sequences and uncertain stratigraphic boundaries2.Shallow gas clouds in the crestal area of the field masking the seismic response in the central area3.Thick coal sequences in B reservoir masking the reliability of seismic attributes4.Poor distribution of exploration, appraisal and development wells across the field with no data in between the clustered wells

The data from geology, sedimentology, geophysics, petrophysics and reservoir engineering was integrated to build a robust static model that is being simulated by reservoir engineering as part of the full field FDP. A significant amount of core was taken during the various drilling campaigns and the team was able to utilize this in order to construct a depositional facies model for the 2 main reservoirs. Lithofacies, rock types and porosity/permeability associations were developed, properties were upscaled into the static model with an average thickness of 0.5m in order to capture vertical heterogeneity, and 3D facies was distributed using various standard modeling techniques.

These methods captured the geology well, explaining the stratigraphic boundaries and different fluid contacts observed in various parts of the field. The new geological model and the volumetric assessment improved history matching and predicting future reservoir performance.

Introduction

Field A is located about 170 km northeast of Kerteh, Terengganu offshore Peninsular Malaysia. It is an East-West elongated anticlinal structure (30km x 15km), with four-way dip closure, several normal faults and a Northeast-Southwest trending central graben. Based on the positive results achieved from the EPS drilling program Management has challenged the Team to deliver Full Field Development in 4 years. Due to the reservoir complexities the Team has found this schedule quite challenging.

Technical Challenges

Thinly Laminated Reservoir Sections

This is a classic issue for many fields, including Field A. The thinly laminated reservoir/non-reservoir sections are seen in conventional cores and have thicknesses below or slightly above electric log resolution (5 to 90 cm). Also, the lateral heterogeneity of these thin laminated reservoirs and their discontinuities across the field makes it more difficult and challenging to capture in the static model. Coals developed within these laminated sands act as vertical barriers while sealing normal faults act as horizontal barriers for oil to move. (Figure 1).