Dual porosity in sandstones is considered as a key parameter that controls hydrocarbon production. Understanding of distribution of secondary pores, might give some insights about the heterogeneity of the reservoir for a particular area and as a result can help to produce more oil applying more efficient well-planning and design techniques. The studied oilfield is located about 40 km offshore Brunei Darussalam. In order to find out mechanisms that could lead to the development of secondary pores number of studies was conducted including helium porosity measurements, Mercury Injection Capillary Pressure, Micro-CT images (µ-CT images), X-Ray Diffraction, Petrography analysis, Scanning Electron Microscopy with Energy Dispersive Spectroscopy and Focus Ion Beam Scanning Electron Microscopes. The results showed that effective porosity that was formed by secondary pores was caused by the erosion, fracturing, and dissolution of sedimentary grains, authigenic minerals that are a part of pore-filling cement, and authigenic replacive minerals.

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