Abstract
ASP flooding process has emerged as cheaper alternative of conventional micellar–polymer flooding. Process has economically produced incremental oil over water flood in field on pilot scale by reducing the capillary forces trapping the oil and improving the overall contact efficiency. Process is designed to combine the best feature and eliminates some of negative aspect of each process of Alkaline, Surfactant and Polymer flooding.
Present paper deals with the application of ASP technology in Viraj field of Ahmedabad Asset. The Viraj rock is sandstone rock with average porosity is 30% and permeability ranges 1-10 Darcy. The reservoir crude has viscosity of 50 cP at reservoir temperature of 81°c with acid number of1.805 milligram per gram of crude oil. Viraj crude is viscous in nature. Hence sharp viscosity/mobility contrast is exiting in primary production mechanism. In view of above, ASP process appears to be best feasible technology for maximizing the ultimate recovery.
A four inverted 5-spot pattern has designed on the basis of encouraging laboratory results. Conventional method of reservoir engineering were applied for performance prediction of oil recovery in the field condition and an additional recovery was estimated 18% of pilot OIIP over water flood (32%). Surface facility and injection schedule was prepared by in-house expertise. ASP plant has been commissioned on 10th August-2002. An MDT team was formed for monitoring the ASP pilot accordingly a monitoring manual was prepared for surveillance. Polymer samples were collected from polymer storage tank, after pumps and at injector well heads for quality control of injection polymer. Wells head samples of all 9 pilot producers and some offset well were carried out for tracer breakthrough/ injected chemicals break through to know the flood front advancement. Three different type of tracers were injected in three injectors followed by ASP slug injection @ 200 m3/d per well. It was estimated that 58000 m3 of additional oil was produced and decrease in water cut of about 10% by ASP process. Before implementation the ASP pilot in July'2002, the liquid production was at its highest@ 1560 m3/d and corresponding oil rate and water cut were 152 m3/d and 89%. After implementation of ASP pilot, water cut declined to 72% by April'2003 and oil production increased to 260 m3/d, indicating the efficiency of ASP flooding. Subsequent rise in liquid withdrawal could not contain water cut rise and regained a level of 80%+. The tracer and chemical breakthrough was observed in almost all the pilot producers and some offset wells. It showed that front was moved uniformly in all direction, same was confirmed later by simulation study. During the pilot implementation imbalance in injection and liquid production was observed due to completion problems of five producer in both the layers, as confirmed by simulation study in April' 2010. Simulation study validated the decreases in oil saturation in pilot area by moving the mobile oil towards down-dip side of structure. This mobile oil by ASP slug was trapped by drilling 9 infill locations and on sidetrack wells. This has led to increased oil production from 100 m3/d in March'2010 to a level of 160 m3/d whereas water cut has remained more or less at around 83%. The cumulative oil produced by these ten infill locations was 98476 m3 as on Nov'2015. A total oil production by EOR and mobilized oil obtained by IOR (infill locations) was 156476 m3 which is about 87% of envisaged oil production from pilot.
The success of this first ASP pilot tested in Viraj field of Ahmedabad Asset, India led field pilot expansion for commercialization.
