Abstract

Asset based functioning in companies has been setting examples of fast track development strategy by combining multi discipline functions. This is especially relevant for development of a marginal field located adjacent to a large gas field, hydro dynamically connected at aquifer level. In the case history of Vasai East field, these aspects are presented here.

3-D seismic carried out in the year 2000 around the existing field provided a lead for possibility of a new structure towards east. The first exploratory well drilled in March 2001 led to discovery of new marginal field Vasai East having oil overlain by large sour gas cap and underlain by large aquifer. The field was delineated by mid 2002 after drilling of four additional exploratory wells. It was also concluded that Vasai East field is separated from main Vasai gas field at hydrocarbon level, but is hydro-dynamically connected through a common aquifer resulting in sub-hydrostatic pressures. Immediately after delineation, fast track development strategy was formulated and a core team was constituted by combining functions of geology, geophysics, reservoir, drilling & well engineering, asset, design and engineering and R&D institutes to workout development plans for the field.

This paper discusses the combined results of a multidisciplinary team for fast track development, technological options, economization of new infrastructures, techno-economic evaluation of different development options. The cost effective development plan with investment of about US$ 200 million was approved by management in shortest possible time for this marginal field.

Since adjoining gas field was being produced at its peak rate, any delay in implementation of this fast track strategy could lead to serious impact of oil recovery of this field. The implementation of this development plan is on fast track execution.

Introduction

Development of marginal fields is being focused by every operator. This is important because a large number of discoveries in recent years are small accumulations and give marginal economic returns. Many authors have presented their approach for development of such fields. Giannnesini [1] et al presented innovative technology to reduce cost. Behrenbruch [2] focused on development planning where as flexible and novel approach have also been addressed by Richardson et al [3], Linda et al [4], and Shaheen et al [5]. Lorenzo et al [6] presented case history to control cost, Bakes et al [7] gives benefits of horizontal wells in Yamm field, Stephen et al [8] presented case history of Telforal field, Odd et al [9] presented a case study of North Sea marginal field. Fras et al [10] presented case study of offshore North West Java. Yu et al [11] presented another case history of offshore marginal field. Similarly Badiyento et al [12] presented strategy for development. Many authors [13–14] have also worked on common aquifer impact.

After discovery of Vasai East, a through review of existing works of different investigators were carried out to frame strategies, plans and activities for fast track approach.

Vasai Field

This field is a giant sour gas producing field, with initial gas reserves of about 284 BCM and thin oil reserve of about 143 MM3. Figure 1 shows the location of the field.

Vasai field is a structurally high area situated on the continental shelf between Mumbai high field to the west and city of Mumbai to the East. It is located about 80 km West North - West of Mumbai city. The water depth over the field area ranges from 50 to 65 mts and is spread over an area of about 250 square km. The field was discovered in 1976 and put on production from September 1988.

Main hydrocarbon accumulation is within Mukta & Vasai Limestone, which is of Middle Eocene to Lower Oligocene age, with small accumulations in Panna (Basal clastic) reservoir. Based on petrophysical characteristics Vasai Limestone has been divided into three zones namely:

  • Mukta (A zone)

  • Tight Zone and

  • Vasai Formation (B-zone).

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