Garraf field is situated in southern Iraq, in Thi Qar Governorate. It was discovered in 1984, and proven to have hydrocarbon accumulation in Middle and Lower Mishrif by exploration and appraisals wells in Garraf. It has low relief gentle anticlinal structure aligned in NW-SE direction and has a dimension of 10km in width x 31 km in length. The Mishrif Formation were deposited in Mesopotamian Basin during the late Cenomanian to Early Turonian. Mishrif is a limestones formation with the approximate thickness of 200m.
Mishrif Formation is the major reservoir and contributes almost 70% of the field's total STOIIP. For the field development plan, a 3D subsurface model was developed for resource assessment and production prediction. However, due to limited wells availability in Garraf, the main challenges are modelling the reservoir continuity and heterogeneity throughout the field to ensure the resulted model represent the actual Mishrif Formation. For the last few years the understanding on the reservoirs were solely based on the regional information, however with the recently acquired conventional core from Mishrif formation and the availability of acoustic impedance from 3D seismic data give an opportunity to investigate the reservoirs in more details.
Information on the depositional environment and the facies distribution are very crucial during the facies and petrophysical modeling stages to ensure the resulted 3D model represent the actual subsurface condition. The objectives of this exercise are to integrate all the information and develop the depositional model and characterise the Mishrif reservoirs.
All microfacies identified were from the core and thin sections and their reservoir characteristics were predicted based on the observation on the compositional and textural variables. Their specific depositional environment were modeled based on Wilson Microfacies Model (1975) and Standard Facies Belts (1975) with broad shelf. Each microfacies identified were grouped into several hydraulic units (HU) based on their flow zone indicators (FZI). Upon the calibration with the cored intervals, the FZIs were extrapolated to the uncored intervals. The rock typing (RT) were compared with the microfacies to ensure its vertically matched with each microfacies distribution. The hydraulic units were extrapolated to the uncored intervals and wells by using multi liner regression. The resulted RTs from this process were converted into microfacies based on observation from the cored wells, acoustic impedance, and regional settings.
