Reservoirs which produce under active water drive offer a significant uncertainty towards implementation of Chemical EOR processes. This paper describes a successful pilot testing of ASP process in a clastic reservoir which is operating under strong aquifer drive. The field has ~ 30 years of production history. The objective of the pilot was to understand response of ASP process in a mature reservoir, which is operating under active edge water drive. The build-up permeability of the reservoir is 2-8 Darcy with viscosity~ 50 cP. Salient key observations like production performance, incremental oil gain, polymer breakthrough etc. are discussed in this paper after completion of the pilot.
On the basis of laboratory study and simulation, ASP pilot was implemented in the field in 2010.The pilot was designed with single inverted five spot pattern and one observation well. The pilot envisaged injection of 0.3 pore volume (PV) Alkali-Surfactant-Polymer (ASP) slug, 0.3 PV graded polymer buffer followed by 0.4PV chase water. The pilot was meticulously monitored for production performance and breakthrough of chemicals. All the pilot producers have more than 20 years of production history. Base oil rate and water cut were fixed before start of the pilot, on the basis of test data which was used to monitor pilot performance. Interwell Tracer Test (IWTT) was conducted before starting of ASP injection so as to understand sweep in the pilot area. In addition, quality of injection water and chemical concentration in ASP slug was checked regularly to ensure best quality.
Significant response of the pilot was observed within 15 months of the start of the pilot which was published in 2012. This paper aims to describe the learning and conclusion after successful completion of the pilot. ~40-50% jump in oil rate was observed during the ASP injection period which sustained for 12-18 months. However preferential breakthrough of ASP slug in one of the producer impacted the incremental oil gain. The preferential breakthrough of polymer was due to presence of high permeability streaks which was rectified by profile modification job. In addition, strong aquifer movement was experienced during ASP injection which leads to rise in water cut of a pilot well. However, the pilot well was restored through water shutoff jobs. After completion of ASP and mobility buffer, a cumulative incremental oil ~28000 m3 was obtained. Cumulative incremental oil gain is in line with simulation studies prediction. 12-14% decrease in water cut was observed which sustained for ~ 6-18 months. Regular monitoring of produced fluid indicated breakthrough of polymer and alkali in 2-3 producers. During the pilot, produced fluid handling issues like tough emulsion formation, lift malfunctioning etc. was not observed. These collective observation indicated success of the ASP pilot project.
There are very few case histories of successful ASP pilot implementation are available, in which the reservoirs has been operating under active aquifer drive. Learning of this ASP project can be taken forward for expansion of ASP flood and also designing of ASP pilot/commercial projects for analogous reservoirs.
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.