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Natural gas production tests and the day after

By Constantinos Hadjistassou

PRODUCTION tests, also known as drill stem tests, are a milestone in the development of a hydrocarbons field and its conversion into a proved reserve.

The process primarily aims at: (a) quantifying the production capacity; (b) determining the pressure of the fluids (oil, natural gas and/or other hydrocarbon gases and fluids within a reservoir; (c) confirming the permeability (flow of the hydrocarbons) and the porosity (volume of hydrocarbons) of the bedrock in the reservoir; and (d) delimiting the area of the formation. Moreover, during a production test samples of natural gas are extracted for chemical analysis to determine the composition and quality of the fluids.

During a production test a small quantity of hydrocarbons is allowed to rise through the drill string and up to the surface. Where offshore prospects of natural gas are concerned, this volume of gas is burned at sea in a process known as gas flaring. Although the importance of flaring is more symbolic than anything else, it is a step that can generate a great deal of optimism. As for the colour of the flame – which has received much coverage in the media – it is expected, depending on the richness of the fuel-air mixture, to be yellowish to golden, reflecting the excellent quality of the natural gas, which is likely to be pure methane.

However, the hydrocarbon deposit acquires even greater value if natural gas condensates are detected along with methane gas. Environmental considerations limit natural gas flaring. For the record, flaring of hydrocarbons is not permitted in Europe except in special circumstances, for example in emergency situations. Also significant is the fact that the production tests will demonstrate whether additional appraisal wells will need to be drilled or whether the gas field can be declared a commercial asset. The conversion of the Aphrodite gas field into a proved reserve, with the assistance of independent experts, would usher in a new era for Cyprus.

In tandem with plans to build a liquefaction terminal, natural gas bonds may be issued to raise the necessary capital for this grand project. It’s worth noting that the liquefaction plant in Cyprus would be the first of its kind on European territory. The commercialisation of the discovery – subsea systems and floating offshore installations, including laying the submarine pipeline that will siphon the natural gas to Vasilikos – can be implemented in a timeline of three to four years.

The bedrock’s morphology in the reservoir is key to developing a hydrocarbon find. In the case of the Aphrodite field, seismic and other measurements have shown that the reservoir is possibly divided into three transverse zones that could be faults in the bedrock. If the field is uniform without crevasses, then it becomes relatively easy to calculate the volume of natural gas (in cubic meters). Measurements using specialised instruments (well logging) from both of the wells (appraisal and exploratory) as well as calculations from simulations using computational models can diagnose whether the reservoir is a single field or not. Based on these data, engineers will be able to determine the need for a second appraisal well. If the odds are stacked in our favour, the Aphrodite reservoir will be found to contain a proved reserve of natural gas of at least 200 billion cubic feet (bcm). One hopes that commercial development of natural gas can act as a catalyst for a rebound of the Cyprus economy and the reining in of unemployment.

Constantinos Hadjistassou is a partner at Energy Sequel (www.energysequel.com) and researcher in hydrocarbons and low-carbon technologies at the University of Cyprus

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