Abstract

Neelam is a heterogeneous carbonate oil field, located offshore India. In addition to aquifer and gas drives, pressure is maintained by water injection. Production is from vertical, deviated and horizontal wells. Severe, unexpected production problems, such as high water cuts and low oil rates, have been encountered. To address these, a multi-disciplinary reservoir study was performed, which integrated available data, and has created a history matched flow simulation model of the field. This model will aid development of strategies to optimise the oil recovery from the field. The characterisation of the field to prepare it for flow simulation was described in another SPE paper (1). There it was shown how diverse types of information, for example well logs and acoustic impedance's derived from seismic data, were integrated using advanced techniques and software to efficiently create an input model for flow simulation. This paper describes the history matching of that model with a fluid flow simulator. It will show that for much of the field, the model actually did not require much modification, thereby validating the approach described in the previous paper. This is noteworthy, given that flow properties of carbonate fields (including Neelam) can be potentially very difficult to capture. However, as will be described, during the history match the model did need development in certain crucial areas. Notably, the areal compartmentalization of the field into separate flow blocks after a major material balance study, and the implementation of high permeability streaks, which were inferred from dynamic data (production logs, production rates and pressures, RFT's). It will be explained that the identification and parametrisation of such streaks was aided by a simple probabilistic technique implemented in an interactive PC package developed by the team during the project. Finally, descriptions will be provided of the strategies, which were developed to efficiently achieve a realistic history match in spite of the difficult nature of the problem. These strategies will be used to suggest some general recommendations on workflow and procedures in integrated reservoir studies.

Introduction

In a carbonate field it is generally a difficult task to calibrate (history match) a flow simulation model so that it accurately reproduces the historical pressure and production behavior of the wells. The task is made more challenging when (as is usual) it has to be performed according to limited timescales and resources. Moreover, the changes to the model, which are required to obtain the history match, must be made in a manner which maximises the reliability of the predictions from the model. It is also crucial that the limits of the reliability should be known.

This paper describes how a history match was obtained for the carbonate Neelam field, using a single porosity, three phase (oil, water, gas) black oil model. The main strategies and techniques, which allowed this to be accomplished within limited times scales and resources, will be discussed. The characterisation of the field to prepare it for flow simulation was described in another SPE paper (1). It will be described that this characterisation provided a sound basis for the match. The main changes to this model, which were required to accomplish the match, will also be described. These were arrived at through multi-disciplinary consensus, thereby maximising the reliability of the predictions from the history matched model, and providing a good understanding about the limits of this model.

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