COMPARATIVE ANALYSIS OF SONIC AND DENSITY LOGS FOR POROSITY DETERMINATION OF “SAMA” FIELD NIGER DELTA, NIGERIA

Abstract

The porosity of a rock is an important condition when attempting to evaluate the potential volume of water or hydrocarbon in it. In view of this, researchers have used combination of porosity logs to determine porosity without the knowledge of knowing which porosity logs has less error. A comparative analysis of porosity values computed from sonic and density logs obtained from SAMA field is undertaken using four wells. The aim is to geostatistically estimate best porosity to be used for accurate hydrocarbon reservoir potential evaluation. The wells, SAMA-001, SAMA-002, SAMA-010, SAMA-012 and SAMA-004 were correlated along the northeast - southwest direction. The Petrophysical analysis which includes calculating the volume of shale, permeability and porosity were carried out. Two prospective reservoirs were delineated on the well logs across the study area namely; R1 and R2 within the depth interval of about 8229 and 8924 ft. across the entire well. The depth beyond this reflect the water- leg such that Gas– water contact (GWC) occurs at depth 8876 ft. The Coefficients of variation of sonic log derived porosity values 32.2%, 26.8%, 24%, 36% were discovered to be less than density log derived porosity values 32.5%, 48.8%, 32%, 40% respectively; therefore, sonic log derived porosity is a more reliable tool for porosity estimation than density derived porosity.