Evaluation of Potential Impacts to Water Resources from Petroleum Drilling - Grand Mesa, Colorado

Thyne, Geoffrey¹ (1) Colorado School of Mines, Golden, CO

Development of petroleum resources in portions of the western US involves drilling and production in environmentally sensitive areas. Many residents have particular concern about impacts to scarce water resources. In 2002, drilling of exploration wells to evaluate Mesa Verde gas resources was proposed for the Grand Mesa, Colorado. This high elevation undeveloped watershed includes national forest lands and recharge areas for the Gunnison River. The watershed also provides flow to agricultural and residential users on the northern side of the river valley.

Pre-drilling assessment of the hydrologic system used hydrologic, hydrochemical and geological data to evaluate the potential impacts to the watershed. Local concerns were centered on the potential for drilling and production activities to directly impact surface and ground water resources based on a conceptual model where deep recharge from the top of the Grand Mesa discharged into the target Rollins sandstone and the shallow aquifer at the base of the Mesa.

The study showed the majority (99%) of ground water flow within the shallow alluvial aquifer is derived from direct runoff with very little recharge from the Mesa Verde interval (<1%). Predicted water production from petroleum wells was very low, 0 to 150 barrels of water production per day (0 to 4.4 gallons per minute) and the amount of water likely to be withdrawn is very small compared to the amount of yearly recharge. Finally, MODFLOW simulation of pumping in the exploratory wells produced no significant impacts (drawdown) on the shallow aquifer that supplies drinking water.

AAPG Search and Discovery Article #90055©2006 AAPG Rocky Mountain Section Meeting, Billings, Montana