Hamra Quartzites (Ordovician) Reservoir Properties Prediction Enhanced by a Combination of Compressional and Shear Slowness

By

 Sissani Agounizera¹, Ahcene Allam¹

(1) Sonatrach Exploration, Boumerdes, Algeria

 The prediction of the reservoir properties for the Cambrian and the Ordovician producing in the Hassi-Messaoud area, is still one of the most important task that needs a big exploration effort to discover new oil accumulations as a satellite of the supergiant Hassi-Messaoud oilfield. In this work, the focus is on the combination of compressional and shear velocities data, as reservoir prediction tool. The most common velocity used in seismic is Vp, the compressional wave velocity (P-Wave ).

A succession of well logs was obtained during a recent discoveries wells, drilled in Hassi-Dzabat, in the Southern part of Hassi-Messaoud field, where the Ordovician reservoir (Hamra Quartzites) was found to be relatively very thick (330 feet). Well logs analysis indicate the presence of an interesting high resistivity pay of 167 feet. The estimated porosities from logs range from 5 to 7 %. No significant shows were recorded during the drilling due to the utilisation of the mud oil for drilling. This interval was tested with an average flow rate of 1600 BOPD.

A full waveform sonic was recorded in the HDZ-2 well. The compressionnal and shear velocities are, therefore, extracted and used to calculate the different elastic properties of the formation (Poisson, Bulk Modulus, Compressibility, Sigma Function, Acoustic / Elastic Impedance, Stonely attenuation...). The preliminary results indicated that the Hamra Quartzites formation can be, at least, subdivided into three (03) individual units that have the same Ç mechanical facies È, which is different from the usual lithofacies description; the medium unit is considered to be the main producing one; the upper unit, characterized by low porosity values, it appears to be more fractured with high permeability values, and shows some interesting correlations when compared with the calculated elastic parameters (Poisson Ration Vs Fractures, Acoustic Impedance Vs High Resistivity Zones...).