Improvement of Vertical Conformance in Injectors - A Must for Fluvial Channel Reservoirs

Abstract

Mangala Field in Rajasthan, India was discovered in January 2004 and began production in August 2009. The main reservoir unit is Fatehgarh Formation, consisting of interbedded sands and shales. Upper Fatehgarh sand (FM-1) has almost 50 % of field STOIIP. It is a fluvial channel sand with excellent reservoir characteristics (average porosity ~ 25% and average permeability of more than 3000 md). Crude is waxy and wax dropout temperature is close to reservoir temperature. This reservoir is being developed by an inverted 9-spot hot waterflood, but a subsequent chemical flood EOR (polymer + ASP) is planned. Currently, an inverted 5-spot pilot program is being carried out to assess the effectiveness of a chemical flood. Initial injection profiling data suggested that vertical conformance was poor, possibly due to poor injection water quality and wax dropout, but it was envisaged that selective chemical treatment of the channel sands would help in improving it. Initially, chemical assisted diversion techniques were applied in two wells which resulted in substantial reduction in ITHP with negligible improvement in conformance. Thereafter, a coiled tubing and straddle packer system was used to ensure correct placement of a series of chemicals targeting different damage mechanisms i.e. wax deposition and scaling issues. Stimulation techniques included increasing the injection temperature of the water for wellbore heatup and wax dissolution, spotting and soaking of surfactants for dissolution of residual wax, followed by pin point injection of 15% HCL for dissolution of scales. Post stimulation injection logs showed an excellent achievement of conformance. An improved surface setup in the EOR pad (water heater, improved filter design) has helped in maintaining the injectivity over a longer time period. The lessons learned from this stimulation technique would prove to be critical for the FM1 sand, where improvement in vertical conformance would result in significantly higher recovery.