Print this pageAAPG Hedberg Conference
Vail, Colorado
April 24-29, 2005
Water
Chemistry Database to Improve Formation Evaluation and Reservoir Simulation in
Low Permeability Reservoirs of Southwest Wyoming
1 Advanced Resources International, Inc., Denver, CO
2 Henry GeoConsulting Services, Englewood, CO
3 IHS Energy, Houston, TX
4 Petro Data Integration, Lakewood, CO
A key factor affecting the economic viability of low-permeability reservoirs in the Rocky Mountains is the occurrence of mobile water at reservoir depths, sometimes in large quantities. Understanding the nature and mobility of fluids in these settings is an important aspect of determining original gas in place, and controlling the cost of finding and development in marginally economic accumulations. Advanced Resources International, Inc., with support from the Department of Energy, is performing a research program (DE-FC-02NT41437) to characterize the nature, distribution and flow paths of moveable fluids in the subsurface of the Greater Green River (GGRB) and Wind River basins (WRB). Goals are to improve resource characterization, water remediation strategies and enhance gas recoveries in these resource-rich basins. Specific project objectives include the following tasks: 1) build a water chemistry database and construct key maps using the data, 2) conduct a field study for an area with known water production problems, 3) develop a conceptual model for movement of water and gas through low permeability basins, and 4) technology transfer to industry.
Historical and contemporary produced water chemical analyses from a number of sources were assembled into an ACCESS database and are also available in EXCEL spreadsheet form. Data were compiled for the Greater Green River and Wind River Basins and include 8000 compositional analyses from 3200 wells that can be sorted by various criteria, including geographic area, formation (of record) and test type. Data were screened for analytical validity of compositional data using standard industry practices. Most historical data samples include standard seven-component analyses. In addition, new samples included stable and strontium isotope analyses, and were collected from Waltman/Cave Gulch fields (WRB), and Pinedale, Table Rock and Wild Rose fields (GGRB) for a total of eighty-five wells.
Preliminary interpretations of data suggest, with some exceptions, little mass movement of waters away from original units of deposition. Produced water compositions generally reflect original depositional environments of their host rocks, modified by chemical interaction with rock matrices during basin evolution. Areas of faulting and vertical transport can sometimes be identified by anomalous chemical and/or isotopic compositions as measured against background regional trends. A general relationship was established between total dissolved solids and water resistivity that facilitates mapping of regional trends in water resistivity. Understanding vertical and lateral variations in water resistivity (RW) is key to accurately calculating gas in place from electric log data.
Water resistivity information from the database was used to constrain inputs to a petrophysical model developed as part of the field study associated with this project, leading to more accurate pay determination and better inputs for the associated reservoir model and simulation. Applying this model could lead to better economics through selective perforation of gas intervals and avoidance of water producing intervals.
From a broader perspective, water chemistry and mobility are important considerations when upscaling detailed petrophysical and stratigraphic interpretations to reservoir-scale production simulations and basin-scale conceptual models: integrating water
data with petrophysics, stratigraphy, structural geology and reservoir engineering provides a more complete characterization of reservoir behavior.
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