Identifying hydrocarbon and shaly zones of Mishrif Formation in Nasiriya Oil Field by using well logs

Abstract

Well logging is the process of recording physical, chemical, electrical and other properties of rock/fluid mixture penetrated by drilling a borehole into the earth crust. Many of these logs are electrical in measurements. Hydrocarbon may exist in a porous and clean formation. That is, gamma ray and spontaneous potential can identify shaly/clean zones while neutron, density, sonic logs or even NMR logs may be used for porosity estimation. Resistivity logging is used to differentiate between formation filled with salty water (low resistivity) and with those filled with hydrocarbons (high resistivity). Mishrif Formation in Nasiriya Oil Field was chosen as a case study. The Nasiriya oil field structure is an anticline with NW- SE trend. Mishrif Formation is the Majer middle cretaceous carbonate in the stratigraphic column of southern Iraq. The result of well logs interpretation for the first five wells showed that a shaly unit separate upper Mishrif (MA) from the lower one (MB). Also, both units MB1 and MB21 are considered the movable hydrocarbon zones. The CPI data reflect that in which good values of porosity of about 0.18 in unit MB1 and 0.2 in unit MB21, besides low values of water saturation 0.28, 0.45 in units MB1& Mb21, respectively.