Refinement of the Weyburn geological model: Overcoming challenges in data compilation and management

Abstract

Abstract Geological characterization in the current phase of the IEA Weyburn-Midale CO 2 Monitoring and Storage Project is focused on adding new data to the already rich dataset from phase I, and also adding new geological data to refine the final model. Adding new data to existing datasets and bringing in multiple sources of other data has proven challenging from a data management point of view. During this phase a revised static geocelluar model will serve as the heart of the data storage component of the project. It can be used by researchers in many diverse fields including: Geomechanics, hydrogeology, wellbore integrity, geophysics, reservoir simulation, geochemical modelling, and risk assessment. This model utilizes geological information from over 900 wells, covers an area of 1865 km 2 around the Weyburn field, and includes all the hydrogeological flow units from surface down to the Bakken Formation.. The Weyburn reservoir is hosted within the Mississippian Midale Beds, one of many south-southwest-dipping strata that are progressively truncated to the northeast by the sub-Mesozoic unconformity. Well density has been increased from Phase I to better refine the zero edges of these subcropping Mississippian units. The model has been improved to integrate geological units not included in the Phase I model, including: 1) an “altered zone” of anhydrite and dolostone at the updip edge of the Weyburn-Midale reservoir. This forms the caprock to the reservoir subjacent to the regional seal formed by the Watrous Formation; 2) the Frobisher Evaporite, a variably thick anhydrite unit present at the base of the reservoir beneath the northern portion of the field; and 3) the Oungre Evaporite, an anhydrite/dolomite unit within the Ratcliffe beds present above the majority of the reservoir. The altered zone, Frobisher Evaporite, and Oungre Evaporite have been added to the model to improve characterization of long-term fluid behaviour in the Mississippian aquifers. Adding these units into the model, with their irregular termination edges, has been a challenge. Stacking structure maps of the Mississippian beds and then truncating them with the sub-Mesozoic unconformity created residual artifacts. These artifacts could not be correctly resolved in the resulting 3D grid. It was necessary to closely delineate the zero edges them using false wells with zero isopach values, then stack these isopach thicknesses to proportionately fill the 3D grid while maintaining their complex morphology. The result has been a more acceptable representation of the architecture of the Weyburn reservoir and hydrogeological flow units above and below the Midale aquifer. Porosity and permeability derived from core analyses have been added to the model for the Midale and Frobisher aquifer units only. Very little core exists beyond these beds, therefore only the Midale and Frobisher were included. Modelling has been done primarily in Petrel, however it has become necessary to use multiple mapping tools and data conversion utilities to best handle the vast quantities of information present in the Weyburn project. Issues in the projection of data in latitude/longitude, North American Datum (NAD) 27 and NAD 83 were rectified by using a standardized well data source, and a consistent methodology for converting between these coordinate systems. This presentation will give an overview of the new geocellular model for Weyburn Phase II and the methodologies for representing the flow unit architecture while highlighting the key obstacles and challenges in compiling large quantities of different types of data from multiple sources.