Integrated Utilisation and Disposal of Produced Effluent in Nearby Oil Fields Provides Better Environmental Friendly and Economic Solution
Authors: Aditva Johri , Rai R. , Sah A.K. 
Published: December 2007

Integrated Utilisation and Disposal of Produced Effluent in Nearby Oil Fields Provides Better Environmental Friendly and Economic Solution.

The utilisation and disposal of oilfield effluent water is of primary concern to every oil producing company, specially, with increasing environmental awareness.

Effluent water is produced in every oil field. However, oil fields operating under active water drive often result in higher water production. In addition, water is required to be injected in a producing formation, specially, operating under depletion drive to provide voidage compensation or EOR. The injection water is normally tube well water.

The present work evaluates all parameters for managing the treatment of produced effluent, requirement of injection water, reducing burden on tube well water and elimination of terrestial disposal and brings out the optimum option of integrated effluent treatment, transportation and re-injection into the formations for enhanced oil recovery.

Introduction

Eleven major oil fields (BL, LN, ST, JT, SB, NK, and BE fields) on the North side of Gujrat, are being operated by ONGC. Some fields are on production for the last 30 years and others for the last 8-10 years. Four major fields (BL, LN, ST and BE) in this area are classified as heavy oil fields having initial oil in of place over 150 million MT. The physical properties of crudes are given as below:-

API at 60 deg. F 16.91 Pour Point (deg. C) 3 Viscosity at 40 deg. C cp 707 Asphaltenes % wt 2.8 Resin,%wt 30.5 Molecular weight 590

Except JT and SB fields, all other fields are operating under active water drive including heavy oil field. Due to very adverse mobility of oil in heavy oil reservoirs, having largely unconsolidated sandstone pay zones with high permeability, the water production has increased in their early years of exploitation. The primary recovery from these fields, therefore, was found to be in single digit.

In order to increase oil recovery from these reservoirs, thermal in-situ combustion based enhanced oil recovery (EOR) is applied, which requires large quantity of injection water. Presently EOR water is being taken from tube wells in that area. The year wise effluent water production and injection water requirement for these fields is given in Table 1 and 2 and is also illustrated in Fig-1.

Till recently, most of produced untreated water was reinjected through effluent disposal wells (Class-II wells) into water acquifer zones at depth &gt;800 mts. where as some effluent was disposed off through evaporation pits. However, stringent environmental regulations, increasing work over and operating costs of disposal wells, and increasing burden on underground potable water has forced to search for alternative strategy.

Oil field water disposal

The disposal of produced oil field water is an important aspect of effluent management. Keeping in view the stringent environmental regulations, optimising cost of treatment and disposal and to protect health of living organisms, oil companies have been adopting one or more of the following options.–Reduction of water production from Source reservoir–Reinjection into non producing water acquifer at higher depth below water table (referred as Class-II wells,).–Treatment and recycling into the producing reservoirs (Class-I wells) for EOR systems.–Environmentally Sound disposal into terestial streams.

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