--> Stratigraphy in Modeling Ground-Water Flow in Siliciclastic Aquifers: an Example from the Woodbine Formation, North Texas, by H. S. Nance and R. E. Mace; #90986 (1994).

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Abstract: Stratigraphy in Modeling Ground-Water Flow in Siliciclastic Aquifers: an Example from the Woodbine Formation, North Texas

H. Seay Nance, Robert E. Mace

When modeling ground-water flow in confined siliciclastic aquifers, researchers need to study stratigraphic factors such as (1) location of confining layers, (2) sandstone-body (aquifer) distribution, (3) sandstone-body connectivity, (4) outcrop (recharge area), and (5) structural features (depth variability and faults). Using well logs and geologic maps, we quantified these factors in the Woodbine aquifer in order to include them in a ground-water numerical model.

The Woodbine aquifer comprises fluvial-deltaic sandstone and shale that are confined above by Eagle Ford Formation shale and below by Buda Formation limestone or Del Rib Grayson Formation shale. Most aquifer sandstone bodies trend northeastward to southwestward from northeastern Cretaceous sand in Oklahoma, northwestern Louisiana, and eastern Texas. However, west-east-trending fluvial sandstones lie in the northwest sector of the study area. Fluvial sandstone bodies are dip-elongate, stacked, and probably well connected. Deltaic-barrier sandstone bodies are individually sheetlike but are separated vertically by shale beds. West-east-trending fluvial sandstone bodies are poorly connected to those trending northeast-southwest. The recharge area is controlled by formation thinning and va ying structural dips. The Sherman syncline may cause ground water from the north to converge with that from the west. The Mexia-Talco fault zone bounds the study area on the east.

Maps of net sandstone, structure, and effective recharge area will be included in a finite- difference ground-water numerical model to predict the impact of future pumping. The model will be calibrated to water levels recorded since 1900. The effect of detailed stratigraphic data on model predictions of regional ground-water residence times, hydraulic heads, and future changes in water levels will be determined by comparing the model with one having uniform recharge and transmissivity.

AAPG Search and Discovery Article #90986©1994 AAPG Annual Convention, Denver, Colorado, June 12-15, 1994