Challenges in 3D Geocellular Modelling of Complexly Faulted - Stacked Reservoirs: Case Study from Existing and Potential Waterflood Areas in Sirikit Field, Onshore Thailand
Authors: Primadi Hari , Charoenpun Tanaporn , Nuada I. Nengah , Matha Sureena 
Published: March 2015

Central Faulted Region (CFR), East Flank Region (EFR), and Greater Sirikit East (GSE) are the main production areas in the PTTEP S1 Consession, part of Sirikit Field, the biggest onshore oil field in Thailand. The Lan Krabu Formation is the biggest contributor for hydrocarbon production, defined as a thick fluvio-lacustrine deltaic sequence consisting of thin alternations of mouthbar deposits, channels and Chum Saeng lacustrine claystone.

The CFR, EFR and GSE regions are structurally complex, each of which is separated by west dipping, basement rooted main fault. The secondary faults are east dipping antithetic and west dipping synthetic faults which run almost parallel to the main fault. For modelling purposes, detail geological correlation across CFR, EFR and GSE has been established. The correlation utilizes the sequence stratigraphy concept by correlating the flooding surface of the fifth order sequence. The shale interval associated with fifth order flooding surface may inhibit vertical pressure communication or vertical oil movement during production time frame.

Given the highly heterogeneous reservoirs in fluvio deltaic environment together with complex faulting system, it is very challenging to build a geological model that represents the detailed geological features of these areas. Selecting the 3D modelling tools is essensial to generate a model with complicated geological features, in a way that reservoir simulation can be performed in an efficient manner.

This paper will share challenges prior to and during construction of the 3D geocellular model, as well as various modelling approaches that have been generated with multi-scenarios and multi-realizations tasks. It also demonstrates how pixel, object and multi-points statistics (MPS) based approaches in facies modelling along with the application of continuous and discrete N/G provide alternative input for the reservoir modelling. The result of this study will be used for flow performance evaluation and further dynamic modelling.

Introduction

Sirikit Field is located in Phitsanulok Basin, Central Plain, onshore Thailand, approximately 400 km north of Bangkok (Figure 1). The Field is the country's largerst onshore oil field located in the S1 concession, currently operated and wholly owned by PTT Exploration and Production. The Field was discovered in 1981 by LKU-A01 well drilled by TSEP (Thai Shell Exploration and Production).

In effort to increase the oil recovery, Waterflood has been implemented within the Sirikit Area. The East Flank Region was the first region to be waterflooded starting in 1995. The EFR was selected for a waterflood candidate based on the fact that it had the least amount of faulting among the regions. Water injection in Central Faulted Region just started end of 2010. The Greater Sirikit East is a relatively new area, discovered in 2006, and it is still producing under primary recovery.