Abstract

Kalol field was discovered in June 1961 and over 500 wells have been drilled so far. The field has multi-layered reservoirs with 11 pay horizons. Layers X and VII have better sand thickness and continuity. Gross lithology is mainly siltstone associated with shale and coal. The permeability ranges from moderate to poor and the primary reservoir drive mechanism is depletion. The reservoir pressure has fallen sharply from superhydrostatic to substantially sub-hydrostatic at present.

An attempt is underway for the first time in onshore areas, India to apply multilateral well technology in X and VII reservoirs with suitable configuration after integrating geological, reservoir and production data to improve oil recovery. Two Pilot areas, one each in horizon X and VII have been selected on the basis of pay thickness and support of water injection. Current oil recovery factors are 6.4% in pilot area of X and 12% in VII. Two such wells, one each in horizon X and VII are proposed to be drilled, having two laterals of 250m each. The relative angle between two laterals will be 60o. The reduction in well spacing from 600-700m to 250m is also good for optimising oil production in tight reservoirs. Improvement in recovery factors to the tune of 1.2% in horizon-X and 3.5% in horizon-VII have been envisaged in 15 years at a favourable IRR with conservative oil price of US$16/bbl.

Introduction

Kalol field is located about 16 km north of Ahmedabad in the Ahmedabad-Mehsana tectonic block of North Cambay basin in western India (Fig.1). The Cambay basin comprises of many small to medium oilfields. Some of them having production history of more than 30 years. Kalol is one such field. It was discovered in June 1961 and put on production in mid sixties. It is amongst the first few finds by the state owned Oil and Natural Gas Corporation (ONGC). One of the major studies of the field was carried out in early eighties by an Indo-Russian team1. On implementation of the recommendations production increased 2 fold to 1620 t/d during 1989-90 and gradually declined to about 800t/d in 1995-96. Another major study namely, Integrated Development Plan2, was prepared in 1996 and the inputs in the form of infill wells and water injection were given. Production increased by about 20% to 1000t/d in 1998-99.

Recently, in a major restructuring exercise ONGC has adopted Asset based concept for exploration and production of its fields located in this part of the country, which is popularly called the Western Onshore Business Unit (WOBU). As a result of this the attention has shifted to revitalization of the old and aging fields.

FIELD DESCRIPTION

The field is developed on a doubly plunging NNWSSE trending anticline, covering an area of about 250sq.km. It is sub-divided by an axial and two transverse faults into 4 major structural blocks namely North, Main, South and West. The main axial fault dips easterly with a throw of 20-30m and is sealing in nature.

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