• seismic
• P32
• P32
• mechanical
• inversion
• fracture
• upscaling

This work is quantitative, statistical and integrated study of the mechanical behaviour of carbonate rocks, which belong to a reservoir in a supergiant gas field. The primary aim of this analysis is to understand if there is a quantitative statistical relationship between seismic discontinuities, which are linked to the regional tectonic fault system, and fractures at log scale detected by image logs. It is interesting to observe if this relationship is also observable in composite logs, which refer to six different wells.
The main drivers of this analysis are facies classification, which refers to the textural pore network of rocks and chronostratigraphic units, which are obtained through sedimentological characterisation and seismic interpretation. First, mechanical analysis of petro-elastic and petro-acoustic properties of facies and chronostratigraphic units is performed, at log scale. Subsequently, the reader finds a brief summary of the existent relationship between mechanical parameters and chronostratigraphic units at seismic scale.
Rock Physics model, which is performed by Sun (“Extended Biot theory”), supports the study evaluating petro-elastic and petro-acoustic curves at log scale. Successively, an assessment of mechanical features of many kinds of curves, which sum up many types of fractures at log scale, where up-scaled to seismic scale, following the Backus-Gilbert method with a seismic support of 2 milliseconds. Furthermore, three-dimensional analysis evaluates the relationship amongst P-Impedance, Confracture (matrix fractures and conductive fractures) and porosity qualitatively, at log scale.

Then, the mechanical behaviour of seismic discontinuities is analysed. Seismic discontinuities are characterised by interpretation of seismic attributes such as curvature and continuity. This step allows us to create five sets of discrete fracture network (DFN). Hence, it is possible to calculate an index of fracturing, which is called P32 (this index means the ratio between fractured area and volumetric unit, which belongs to geo-cellular grid 100x100x8 metres).

P32 is compared to elastic parameters such as P-Impedance and Poisson’s Ratio, which are obtained through an elastic Bayesian Inversion “Sparse Spike”. Then, six composite logs, which belong to six different wells in the supergiant gas field, were analysed. Thereafter, seismic envelopes were extracted which detect the presence of seismic discontinuities around each well at a distance of 10, 20, 30, 40 and 50 metres.
In conclusion, the most important aim of this analysis is reached: there is a relationship between seismic discontinuities and matrix, conductive fractures from a petrophysical and geophysical points of view, considering the chronostratigraphic distribution of these discontinuities and composite logs.