Abstract

The Mangala Field is the largest discovered oil field in Barmer Basin, Rajasthan, India. The field contains medium gravity viscous crude (10-20 cp) in high permeability sands. The field is being developed under pattern and peripheral water injection. Due to the adverse mobility ratio, waterflooding is expected to result in lesser sweep and ultimately affect oil recovery. The potential for chemical enhanced oil recovery (EOR) has been recognized from an early stage in the field development, with polymer flooding identified for early implementation, followed by staged-wise implementation of Alkaline-Surfactant-Polymer (ASP) injection. To understand and evaluate the efficiency of chemical flooding, a closely spaced normal five spot EOR pilot is being conducted in the fluvial FM1 reservoir units of the Mangala Field.

Polymer injection in the pilot commenced in August 2011, with a series of short term polymer injectivity tests including multi rate test in one of the injectors. These tests provided useful insight about polymer rheological characteristics under reservoir conditions. Non-Newtonian behaviour of the polymer helped in injecting the ~30 cp solution within the designed surface pressure. Radial well modeling confirmed the shear thinning characteristics of the polymer which were in agreement with laboratory data, and that there has been no significant mechanical degradation of the polymer inside the well. Production logging conducted before, during and after the injectivity tests also show no significant change in injection profile as a result of the polymer injection. The injectivity test establishes that polymer injection is viable in Mangala reservoirs. The pilot results are important for an early implementation of fieldwide EOR in the Mangala Field.

This paper presents details of the polymer injectivity tests including bottom-hole pressure measurements and production logging conducted during the tests. Details of the single well fine scale modeling to match the injectivity test pressure behaviour are then described.

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