UTILIZING CORE AND NMR DATA TO IDENTIFY ROCK-TYPE AND PORE THROAT RADIUS FOR MISHRIF FORMATION IN WEST QURNA OILFIELD

Abstract

The middle Cretaceous Mishrif Formation represents the main carbonate reservoir in southern Iraq, charactered by heterogeneity and complexity vertically and laterally, this reservoir encompasses six facies that graduated from mid-ramp facies to supratidal facies. Mishrif Formation in West Qurna oilfield consists of three main reservoir units namely mA, mB1 and mB2 with two cap rocks units CRⅠ and CRⅡ. Rock type and pore throat radius govern the relationship between porosity and permeability. Porosity and permeability are important petrophysical parameters for reservoir evaluation and can be determined directly from core analysis or indirectly using the NMR logging tool. Core data from four wells and NMR data from one well were used to determine the rocks type and the pore throat radius. In this study, Lucia rocks type plot between the porosity and permeability was used to define the classes of Mishrif units’ characteristics. Rocks type of Mishrif Formation was wackestone and packstone in mB2 unit. The mB1unit exhibits increasing in the grain dominated class1. Whereas, unit mA showed a mud-dominated class 3 again. Winland plot was utilized to determine the pore throat radius depending on the mercury injection test with 35% mercury saturation. The unit mB2 marked as mesopores and macropores. Megapores and macropores attribute increased in mB1in the northern part of West Qurna oilfield unit due to increasing shoal and rudist bioherm facies, the mA unit revealed increasing in meso-porous and decreasing in mega-porous. NMR data was correlated with core data and the results supported this reservoir characteristic.