In the Central Luconia area, offshore Sarawak, substantial gas reserves are present in Miocene carbonate buildups. The carbonates consist of limestones and dolomites with porosities ranging from 0 to 40 percent. From core analysis it became evident that there exists a potential problem with regard to the compaction of the carbonate reservoir matrix as a result of effective stress increase as the reservoirs are depleted. Triaxial compaction tests were carried out on core samples from several carbonate reservoirs. It was found that highly porous mouldic limestones show pore collapse at relatively low effective stresses. After pore collapse the uniaxial compressibility coefficient increases significantly.

Reservoir compressibility parameters can be derived from core data, for collapsing as well as non-collapsing rocks. These can be used to calculate reservoir compaction from well logs for o particular pressure decline. An estimate of the expected surface subsidence can be made based on the theory of poro-elasticity and the nucleus of strain concept as described by Geertsma. Predicted subsidence figures have been taken into account in platform design.

The gas reservoirs have large aquifers within the carbonate buildups. As these aquifers have not all been fully appraised, there exists some uncertainty concerning their actual compaction behaviour.

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