Geomechanical Approach for Rock Strength and Lithology Anisotrophy of Jurassic Carbonate Manusela Fracture Reservoir from Oseil Field



The geomechanical relationship between lithology and rock strength reveals a new method for fracture study and analysis. This practical geomechanical application is also valuable for drilling parameter design and could create a new way of fractured field development. In order to simplify complications in the Jurassic carbonate Manusela fractured reservoir we used the geomechanical as approach. The method of geomechanical core interpretation and analysis of our carbonate fractured field is as follows: stress in the earth is simplified by using Smax and Smin system; all failure is simplified into shear and tensile fracture; tensile strength of rock is much smaller compared to compressive strength; evidence of multiple tectonic phases such as extension, surface exposure and compression are key for fracture development; diagenesis of cementation and compaction creates higher rock strength; rock strength of Manusela carbonate is calculated from sonic log by using equation, drilling well data and triaxial test; direct relationship between helium porosity and rock strength is found in Oseil-1 well. We are proposing new ways for fracture analysis by combining calculated rock strength and lithology. Higher rock strength has fewer fractures and less porosity whereas less rock strength has more fractures and more porosity. In E Nief-1 well, compacted Dolostone core has the highest rock strength (average 10500 PSI), less fracture and non reservoir. Oolitic limestone core at this well has less rock strength (average 7200 PSI), more fractures and good reservoir. In Oseil-1&4, Oolitic limestone dissolution core zone has less rock strength (average 7500 PSI) and Dolostone has little bit higher (7900 PSI), both zones of Limestone and Dolostone has highly fractured and highly porous. Manusela carbonate rock strength and lithology anisotropy may be able to be derived from cores measurement. The fracture anisotropy parameters derived from cores are important input parameters f o r a m p l i t u d e v e r s u s a z i m u t h m o d e l i n g .

Key words: Geomechanic, Manusela formation, Carbonate fracture.


Authors : Anggoro S. Dradjat, Christian Sony Patandung