Abstract

ZeroGen-11 is the first pilot CO2 injection well, air drilled by ZeroGen in the North Denison Trough. Its objective was to evaluate low permeability saline aquifers for suitability to commercial scale CO2 sequestration by investigating the injectivity of super-critical CO2 and brine, reservoir ‘k.h’ (permeability-thickness), reservoir continuity. Key activities were the CO2 and water injection test design, well site operations and the interpretation of the ZeroGen-11 CO2 and water injection fall-off test data.

A series of CO2 injection tests and a single water injection test were carried out in ZeroGen-11. The detail design of the tests and selection of various intervals were based on continuous cored data, rock typing, and low cost appraisal wells. The materials for well tubulars were CO2 resistant (13Cr).

Pilot operation activities commenced in mid 2009 and, being the first open-hole CO2 pilot in saline aquifer with unusually low permeability, they faced significant challenges. Operational data from the Australian wellsite was analyzed real time at the Shell Bangalore Technology Centre "Collaborative Work Environment" by an integrated team of discipline specialists which helped for the optimization of ZeroGen operations. The operational experience gained is valuable for low rate injection tests, at high pressures in an open-hole interval under compressive stress regime where fracture gradients as high as 1.1 psi/ft are possible.

The test results established supercritical injectivity of CO2 in matrix condition for high permeable Catherine Sandstone interval at rate of 150 TPD and in low permeability Aldebaran formation at 2-3 TPD. The well test interpretation gives ‘kh’ in the range of 1 md.ft for Aldebaran and 240md.ft for high permeability Catherine Sandstone. The water injection test provides a reasonable calibration point to determine CO2 injectivity, and is expected to be useful in appraisal campaigns in saline aquifers. It is also noted that the CO2 injection test did not show a two boundary signature in the pressure derivative curve that was clearly observed for the water injection test as the presence of CO2 zone near wellbore mask the effects of a boundary signature.

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