- Copyright © 2003 Society of Exploration Geophysicists
Prolific gas production originates from the Permian Khuff carbonate reservoirs in the Ain Dar/Shedgum area of Saudi Arabia's giant Ghawar Field. However, well productivity is highly variable due to rapid lateral variations of porosity and permeability, which are mainly controlled by changes in depositional facies and diagenesis.
Within the study area (Figure 1), average well spacing at the Khuff level is on the order of 4 km. Given this sparse control, it is difficult to map interwell variations in reservoir quality from well data alone; this leads to suboptimal infill drilling locations and uncertain reserve estimates. A key challenge in this study was to improve the description of reservoir heterogeneity by using 3D seismic to guide the interpolation of well data.
Fortunately, high-quality seismic data are available over the Khuff in Northern Ghawar. This enabled construction of a detailed 3D geocellular model of lithofacies, porosity, and permeability by careful integration of an inverted acoustic impedance volume with log and core data. The improved spatial resolution offered by the seismic-constrained model has had a major impact on the identification of good reservoir quality trends, and a number of successful wells have since been drilled, based on the model. Moreover, a significant increase in gas reserves resulted from delineation of higher than expected porosity trends. This increase in pore volume was independently confirmed by an improved pressure match in simulation, achieved using the seismic-derived 3D model.
The Khuff Formation in Ghawar has been divided into four regionally identifiable units, designated in order of increasing age as A, B, C, and D. In the northern part of the field, the Khuff is gas-bearing only in B and …