Abstract

Ravva oil and gas field is located offshore, eastern India, in the shallow waters of the Bay of Bengal. The field is operated by a Joint Venture of which Cairn India Ltd. is the Operator. The field has completed 15 years of production from Middle Miocene reservoir, with over 9 years on plateau production of 50,000 BOPD. The field has two oil blocks, designated as RA/D block and RE/F/B block. The latter is the smaller of the two: it accounts for nearly a quarter of Ravva STOIIP. Until an integrated reservoir modeling study was undertaken in 2004/05, the RE/F/B block was generally recognized as an area with poor understanding of structure and hydrodynamics. This lack of understanding was attributable to three main factors:

  • attenuated seismic response in the central RF area due to the presence of gas at the shallower Late Miocene level

  • complex compartmentalization with low net-to-gross and

  • the Class II AVO response presented by hydrocarbon-charged Middle Miocene reservoir sands.

To overcome these challenges, shear reflectivity (Rs) data, in conjunction with derivative rock property attributes and validated by dynamic pressure data, was used to develop a new geological model: the basis of an infill drilling campaign comprising of one producer and two injectors. The infill drilling campaign has now been carried out and the proposed wells have achieved their objectives.

This paper presents the novelty of the multi-disciplinary approach, in which shear information, inherent in the p-wave seismic gathers, was leveraged and integrated with reservoir pressures and other geotechnical data to make a representative model and realize a successful drilling campaign.

Introduction

Ravva field is a shallow offshore oil and gas field in Block PKGM-1, which lies in the Krishna-Godavari basin mostly off the coast of the state of Andhra Pradesh in eastern India (Figure 1). The field was discovered in 1987 by ONGC Ltd and production commenced in March 1993. A PSC for exploration, development and production of Ravva field was signed in Oct 1994 between the Government of India (GoI) and a consortium consisiting of ONGC Ltd, Videocon Petroleum Limited, Ravva Oil (Singapore) Pte Limited and Command Petroleum (India) Pty Limited, with Command Petroleum being designated operator. In 1996, Cairn Energy PLC acquired Command Petroleum and assumed operatorship of the Ravva field. As at the date of paper, Ravva field has produced around 220 MMboe of hydrocarbons, excluding satellite gas.

Ravva field production levels, which were of the order of 3,700 BOPD before execution of PSC, were increased by the Ravva JV, first to 35,000 BOPD in the second quarter of 1997 and subsequently to a higher plateau rate of 50,000 BOPD in the first quarter of 1999. To date, the field has completed nine years on its plateau production of 50,000 BOPD, and is about to enter its decline phase.

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