Design of an ASP Pilot for the Mangala Field: Laboratory Evaluations and Simulation Studies

摘要

Mangala is the largest discovered oil field in the Barmer Basin of Rajasthan, India having a STOIIP of over 1 billion barrels in multiple stacked fluvial clastic reservoirs. It contains medium gravity (20-28oAPI), waxy, viscous crude (9-17 cp) in high permeability (1-25 Darcy) clean sandstone reservoirs. Initial development plans for the field are based on waterflooding, with at least the initial volumes of water heated to minimize any issues with wax dropout in the reservoir. Owing to the relatively high oil viscosity and adverse mobility displacement for waterflooding, the desirability of implementing an appropriate EOR process was identified shortly after the field discovery. Screening studies identified aqueous-based chemical flooding processes as the most favorable for Mangala. Detailed laboratory studies have now identified the potential of alkaline-surfactant-polymer (ASP) processes in significantly improving the sweep and displacement efficiency. The laboratory studies involved screening and optimization of the ASP slug formulation based on IFT measurements, adsorption measurements, polymer rheological and thermal stability studies;followed by a series of linear and radial corefloods. Experiments indicate the ASP process is the most effective chemical EOR process for Mangala, with improvement in recovery efficiency above the waterflood recovery of over 30% STOIIP. Chemical EOR simulations with STARSTM have been used extensively to understand the process mechanisms via matching of the coreflood experiments. Simulation parameters tuned to the laboratory data were used to evaluate the process performance under field conditions. A closely spaced five-spot pilot with 100m well spacing has been designed to evaluate the process. The pilot consists of four injectors, the central producer, three saturation monitoring wells and two post-pilot core holes. An ASP pilot will be implemented in the field shortly after startup of the waterflood.