Abstract

Water flooding is the most successful and widely used process for effective pressure maintenance and enhancing the oil recovery because water is widely available and inexpensive relative to other fluids, easy to inject, and highly efficient in displacing oil. For water floods, through continuous surveillance plan, reservoir monitoring and water front tracking results in improving sweep efficiency and enhancing the overall oil recovery.

Minagish Oolite (MO) reservoir is a mature reservoir having long production history along with water injection from several years as a primary means of pressure maintenance. In MO reservoir, two types of water injection methods are implemented i.e. power water injection (PWI) and Dump Flood Injection (DFI).

For water injection monitoring and water front tracking a semi analytical model is developed for MO reservoir based on radius of injected cool water front superimposed over seismic and geological cross-sections to monitor the water front position at real time inside MO reservoir. The radius of expanding cool injected water front is obtained by saturation logs (TDT) and layer wise cumulative water injection at various points across the formation. The layer wise cumulative water injection is calculated from production logs on injectors as well as nearby offset producers.

The water injection monitoring techniques based on focused surveillance program and semi analytical model has been developed for both DFI (Dump Flood Injectors) and PWI (Power Water Injectors) which is used for improving water flood conformance in MO reservoir.

In case of MO reservoir the semi analytical model along with Hall plot and its derivative function at sand face is found to be an alternative to pressure transient analysis,

pressure fall off tests, injection tests and tracer survey analysis used for water front tracking and water injection conformance. The methodology has proven to be the best tool for monitoring the performance of both PWI and DFI wells in Minagish Oolite reservoir.

Based on the water conformance modeling, the correct decisions regarding the various workover related to water injectors as well as producers were taken to control the injection water movement through faults, channels and high permeability layers inside MO reservoir. This in turn resulted in uniform pressure maintenance, reduction in water cut as well as minimizing the risks of by passing the oil behind the injectors.

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