DETERMINATION OF PORE TYPES AND POROSITY TRENDS USING OF VELOCITY-DEVIATION LOG FOR THE CARBONATE MISHRIF RESERVOIR IN HALFAYA OIL FIELD, SOUTHEAST IRAQ

Abstract

Halfaya field is located south of Iraq towards southeast Amara city in Missan. Mishrif Formation is a major reservoir in Halfaya Oilfield and is one of the principal carbonate reservoirs in central and southeastern Iraq. The aim of this study is to predict pore types using well logs data at missing core intervals. This study includes calculating the velocity deviation log for the Mishrif carbonate reservoir in two wells in Halfaya oil fields (HF-1 and HF-2) by converting porosity-log data into a synthetic velocity log by means of a time-average equation. A velocity-deviation log, which is calculated by integrating a sonic log with a neutron-porosity or density log, provides a means of obtaining downhole details in carbonates about the major pore forms. These data can be used to track the downhole distribution of diagenetic processes and their effects on secondary porosity trends. The differences are plotted as a velocity-deviation log between the actual sonic log and the synthetic sonic log. These velocity-deviation logs reflect the different physical rock markings of different types of pores: (1) Positive velocity deviations mark areas in which pore types form frames dominate; (2) zero deviations indicate periods in which the rock lacks a rigid frame and exhibits dissolution porosity or microporosity; and (3) Negative deviations mark areas in which sonic velocities are remarkably low due to cavernous borehole walls, fractures or possibly high free-gas content. &nbsp