Abstract

Jhalora field, discovered in 1967, is located in the Ahmedabad-Mehsana tectonic block of Cambay basin in India. Reservoir and crude oil properties of all the three main producing sands K-III, K-IV and K-IX+X are quite different. Viscosity of K-IV sand is ~30-50 cp and permeability varies between 1.9 to 8.7 Darcy. Acid number of crude oil is quite high. Water cut is between 80-85%. The mature stage of the Jhalora K-IV with heterogeneous reservoir characteristics and unfavourable mobility ratio makes it an ideal choice for application of chemical EOR technique to enhance the recovery. Based on extensive laboratory and simulation studies one inverted 5-spot pilot was designed. The laboratory studies envisaged additional displacement efficiency of about 23% of Oil Initially in Place (OIIP). Pilot envisaged injection of 0.3 pore volume (PV) Alkali-Surfactant-Polymer (ASP) slug, 0.3PV graded polymer buffer followed by 0.4PV chase water. In order to check preferential movement in the pilot area, profile modification job was done before initiation of pilot. To monitor flood front movement, chemical tracer was also injected.

A meticulous monitoring schedule was drawn. Monitoring is done by measurements of pH, turbidity, Dissolved Oxygen, concentrations of alkali, surfactant & polymer of ASP slug being injected on regular basis. Monitoring schedule also involves fortnightly checking of production rates for each well & weekly testing of water cut. Well head samples from pilot wells are collected on weekly basis and analysis of produced water for presence of tracer & chemical breakthrough is carried out.

In this paper brief results of laboratory investigation leading to implementation of ASP pilot are given. Detailed results of monitoring, problems encountered along-with various steps taken to ensure smooth injection and performance analysis of this pilot so far are given.

Initial results of the ASP pilot are encouraging with additional oil gain of about 47000 bbls after injection of about 0.17 PV ASP slug and expansion of the pilot project is being planned.

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