Abstract

ASP process is the current worldwide focus of research and field trial in chemical enhanced oil recovery. The process has potential to enhance tertiary oil recovery by reducing the residual oil saturation left after prolonged water flooding in depletion type of reservoir.

The present paper presents the results of the pilot test in K-XII sand of Kalol field in Ahmedabad Asset of ONGC. Kalol field is a multi-layered reservoir having 11 hydrocarbon pay zones. It is a depletion drive type reservoir and was put on production put on production in 1966. Since 1972, central line drive injection pattern was in operation for pressure maintenance and improvement in oil recovery. K-XII reservoir has produced about 30% of OIIP with the help of water injection. It is a light oil reservoir having viscosity of about 0.38–1.87 cP at reservoir temperature of 82°C and permeability varying from 20–700 mD. The acidic component is 0.10 mg of KOH/gm of oil.

After extensive laboratory and simulation studies, a small pilot consisting of 1 injector and 2 producers in line drive pattern and 1 offset well was selected for pilot testing. Single Well Chemical Tracer (SWCT) test was conducted to know the current saturation in the pilot area and was found to be 26%, which was coinciding with the laboratory determined ROS value. This indicates that pilot is almost flooded and saturation is close to residual oil. Injection commenced with injection of 20% of Ammonium Thiocyanate tracer in Oct. 2013 to monitor the front movement. ASP injection started in Feb. 2014.

ASP solution consisting of 0.30 Pore Volume (Alkali −3.0 Wt.%, Surfactant-2000 ppm, Polymer – 300 ppm) has been injected and injection of 0.20 PV of mobility buffer (300 ppm) started in May 2015, which will be followed by chase water. The results of last 15 months of the pilot are encouraging and incremental oil produced is about 3876 m3 (June 2015), which is about 68% of the envisaged oil through simulation. Average Water cut reduction is about 10–15 %, however, significant water cut reduction was observed in one offset well, from 87% to 40 %. The effectiveness of the pilot is also reflected in the production of oil in form of emulsion which was generated in-situ by reaction of oil with alkali and surfactant.

This paper discusses the details of the laboratory studies, simulation study, pilot design, injection schedule, monitoring of injection fluid quality, production performance and lessons learnt. The success of this pilot leads to expansion and application of this CEOR process to other major reservoirs of Kalol field.

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