Production of oil & gas has very big influence to mankind civilization but the excessive generation of produced water in mature fields as a by-product may have bad impact to environment. Pollution of surface water supplies or fresh water aquifers has become a serious concern in recent years. It is therefore an obligation upon the industry to handle the produced water and disposed it responsibly. This concern has focused attention on produced water re-injection into underground formation (whether it is virgin or depleted reservoir) as a promising method to discharge oilfield water without polluting potable water supplies.

DESIGNING AN INJECTION PROGRAM OF PRODUCED WATER RE-INJECTION IN MATURE FIELDS

Rudi Rubiandini Ria S., Eko A. Fitnawan, and Kalwant Singh, Institut Teknologi Bandung

Abstract

Production of oil & gas has very big influence to mankind civilization but the excessive generation of produced water in mature fields as a by-product may have bad impact to environment. Pollution of surface water supplies or fresh water aquifers has become a serious concern in recent years. It is therefore an obligation upon the industry to handle the produced water and disposed it responsibly. This concern has focused attention on produced water re-injection into underground formation (whether it is virgin or depleted reservoir) as a promising method to discharge oilfield water without polluting potable water supplies.

As refer to regulatory guidelines, injection well for produced water disposal must be operated so that the pressure during injection does not initiate new fractures or propagate existing fractures in the confining zone adjacent to the sources of drinking water, which could damage the receiving layer or cap rock. In order to achieve that purpose, the paper describes evaluations and planning on operational aspects regarding daily activity/practical operation, which are essential to the successful of water injection project. Operational aspect especially includes working pressure along the injection system, estimated formation fluid pressure as function of cumulative injected water, estimated fracture pressure and its relation to proposed injection rate. Operational window for injection must be developed to determine the range of allowable injection pressure and its relationship with the proposed injection rate.

The paper also describe a method to determine the life time of each proposed injection well which is the compilation from the result of operational design analysis and reservoir pressure builds up data from simulation results. This study is very useful to make injection programs and scenarios to extent the injection lifetime (e.g. scenario to add new injector wells).

Introduction

Production of oil and gas in Indonesian mature fields has also resulted on a tremendous volume of produced water. Conventionally, operators have been disposing this produced water into the surface (stream and sea). Nowadays, surface disposal is facing the people increase of environmental awareness and protests have been addressed to operators to be responsible for fishpond damage.

After so many years of oil exploitation in Indonesia, the government has not been issued any regulation for especially controls the injection of produced water into underground formation. Basically, efforts should mainly stressed in maintaining the isolation of injected water to the ground water other than limitation of its chemical contents. When re-injection of produced water is chosen, confinement of the injected produced water within the target strata is the key to the environmental acceptability of the injection process. According to some international references, general considerations in produced water reinjection are as follows:

􀂃The selected formation for injection target must be isolated from fresh or potable water zone.

􀂃Injection pressure must be dictated by fracture pressure limitation.

􀂃Injection wells must be well constructed to isolate it from any potable water source.

􀂃The selected formation has an adequate porosity-permeability and reservoir volume.

Fig. 1 shows the complete framework in designing a produced water reinjection project. However, this paper will only emphasizes in designing operational aspect of produced water reinjection and Tambora field as an example case. As shown in Fig. 1, evaluation on injected sand candidate (includes sand quality, quantity, and continuity), reservoir simulation to get pressure build due to injection, and well injectivity performance, should be conducted prior designing operational aspect of produced water reinjection.

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