VERTICAL - HORIZONTAL PERMEABILITY RATIO IN INDONESIAN SANSTONE AND CARBONATE RESERVOIRS

Geology in the Indonesian archipelago is characterized by high level of complexity. Consequently, various petrophysical properties of the reservoir-forming rocks also tend to show high level of complexity and variety. In day-to-day practice this situation is normally called ‘high degree of heterogeneity’. The most important implication of this level of rock heterogeneity is that it affects the reservoir rocks physical properties immensely. This situation certainly creates additional concerns in any activities that involve the rock petrophysical properties such as the much required vertical-to-horizontal permeability ratio. Thorough studies have to be spent for better understanding upon this heterogeneityrelated fact. This paper presents results of a study on permeability anisotropy - in this case vertical-to-horizontal anisotropy - in Indonesian reservoirs through the use of core analysis results. The indicator used for representing the anisotroopy is ratio between vertical and horizontal permeability values. The study involves 14,634 core samples, of which 6,689 are pairs of vertical and horizontal plug samples and 1,256 are full-diameter core samples. They are taken from 259 wells representing 157 fields in all 15 Indonesia’s productive sedimentary basins to date. The core samples cover a wide lithology spectrum from sandstones to various limestones. The work that is performed through a series of classifications, comparisons, and analysis has indeed shown the complexity as expected, even though differences can still be distinguished among groups of classification. Results of the study also show evidence that is on the contrary to the commonly accepted information such as permeability of unity for most sandstones and larger permeability ratio for carbonate rocks. This paper offers immediate useful information to practicians who are involved in reservoir characterization and reservoir modelling related activities.