Abstract
The Viraj oil field lies in Ahmedabad-Mehsana tectonic block of Cambay Basin in India. The field has been under exploitation for the last nearly two decades and produces 18.9°API oil from the sandstone reservoir with an average porosity of 30%and permeability ranging from 4.5 to 9.9 Darcy. Reservoir temperature is 81°C and initial reservoir pressure is 135 kg/cm2. Ultimate oil recovery estimated from the field, producing under active water drive, is 32 % of OIIP.
After analyzing the rock and fluid properties, extensive laboratory studies were undertaken on native cores by R & D institute of ONGC to evaluate the efficacy of Alkaline – Surfactant – Polymer (ASP) process in Viraj field. Laboratory studies indicated an incremental oil recovery of 18 % of OIIP over water flood. On the basis of these encouraging results, a pilot was designed with four inverted 5-spot patterns. Facilities have been created to ensure proper dosing of chemicals, optimum fluid injection and monitoring of injection fluid quality. A comprehensive data-acquisition strategy has been adopted right from the beginning. First phase of the pilot i.e. injection of Pre-flush and ASP slug(20 % PV) having composition of 1.5 wt.% alkali, 0.2 wt % (100% Active) surfactant and 800 ppm anionic polymer have been completed.
This paper aims to present salient features of the laboratory findings and the ASP pilot in progress. The data generated during the first phase of the pilot analyzed and presented in this paper shows encouraging results. Final evaluation of the pilot is, however, planned after completion of the targeted ASP/Polymer/Chase water injection.
