Combining high-resolution sequence stratigraphy and mechanical stratigraphy for improved reservoir characterisation in the Fahud field of Oman

Abstract

In the Fahud field of Oman, the integration between hierarchies of sequence stratigraphic units and fracture systems has proven to be crucial to explain the distribution of flow and mechanical units. The study focused on the Upper Cretaceous, Albian to Lower Cenomanian Natih e unit (Natih Formation, Wasia Group), a 170-mthick carbonate sequence/reservoir, which exhibits heterogeneities in both facies and reservoir quality. Based on a core-derived high-resolution sequence stratigraphic analysis, the Natih e reservoir can be subdivided into four orders of depositional cycles (from 6th- to 3rd-order). Each cycle consists of a transgressive and regressive hemicycle with characteristic facies and rock properties. The facies and diagenetic overprint of the higher-order cycles vary according to their position within the 3rd-order sequences. Analysis of core, borehole images, seismic, tracer and production data indicate a hierarchy of fractures and faults that seems to follow the stratigraphic subdivisions. A relationship between depositional and diagenetic architecture of the cycles, and the aforementioned data, led to the identification of mechanical layering and stratigraphy within the reservoir. This finding was validated and supported by the successful history match of the three-phase production data within the dynamic model of the reservoir. The combination of sequence and mechanical stratigraphy provides a framework for the correlation of facies and mechanical units across the field. Furthermore, the facies and mechanical units are related to reservoir quality and fracture distribution for consistent upscaling into large-scale reservoir models. Through close co-operation between geologists and reservoir engineers utilising dynamic data, it was possible to determine the most appropriate scale for flow and ensure that such a scale was then used as input for dynamic modelling and for planning of the future exploitation of the Fahud field. As a result of this study, Petroleum Development Oman (PDO) has evaluated a 20% increase in risked reserves, and a 25% reduction of well costs.

Assess Impacts of Well Configuration and Boundary on CO2-Based Geothermal Production Using Response Surface Models

“…The study reservoir is simplified from Shu'aiba limestone formation in the Daleel oil field, Oman [7]. As illustrated in figure 1, the model domain is 3km*2km*20m by xyz.…”

Ratana Field, Potwar Fold Belt, Northern Pakistan: High Intensity Fracture Zones Related to Major Thrust Faults as Revealed by Seismic Fracture Prediction

“…Fracture interpretation is typically considered in the framework of present-day mechanical stratigraphy, the division of a sedimentary succession based on the mechanical properties of the layers (Erickson, 1996;. Fracture networks are commonly controlled by variations in mechanical properties at an outcrop scale and outcrop analogues can be used to predict fracture patterns in the subsurface (Corbett et al, 1987;Morettini et al, 2005;Laubach et al, 2009;Zahm and Hennings, 2009;Torrieri et al, 2021). Mechanical conditions such as rock properties, the thickness of beds and the interface conditions between beds all affect fracture development, intensity and orientation (Shackleton et al, 2005;Olson et al, 2009;Laubach et al, 2009;Barbier et al, 2012).…”

Evaluation of Gas-Based EOR Methods in Gas-Invaded Zones of Fractured Carbonate Reservoir

“…These fractures are then occupied mainly by only one phase. Several Middle Eastern fields, such as the Fahud, Gachsaran, and Hafkel [2][3][4], reported large water-and gas-invaded zones during the primary production. For example, the Hafkel field, with more than eighty years of production, has resulted in a gas-invaded zone of around 1000 feet [4].…”