3M Model for San Juan Basin Situation: 

Norwest prepared a basin-wide coalbed methane reservoir model of the Colorado portion of the San Juan Basin for the Southern Ute Indian Tribe, the Colorado Oil and Gas Conservation Commission, and the Bureau of Land Management. The model, referred to as the 3M CBM MODEL, simulates the effects of production from all existing and proposed Fruitland coal wells in Colorado. The effects of dewatering, gas adsorption and desorption, and historical production are included in the model. The model also provides a technology to evaluate coal bed methane infill drilling and gas seepage at the outcrop. Solution:  Due to the size and scope of the input data, it was determined that existing commercial coalbed methane simulators were not suitable for this project. Norwest wrote and customized a new model for the project complete with key features including the handling of 50,000+ gridblocks, thousands of wells, up to 1,000 years of modeling, extremely efficient solver algorithms, outcrop boundary conditions, and input and output using Excel spreadsheets and/or Access databases. The model utilizes the standard Langmuir isotherm to account for gas adsorption in the coal and also allows for free gas in the cleat system of the coal.  Result: The 3M CBM MODEL predicted gas seepage had occurred and would continue to occur in areas previously observed.  When the outcrop was modeled with a perfect connection to the basin, the simulated gas seepage was 10 – 100 times higher than observed levels of seepage. Results indicated that such a perfect connection does not exist in nature; otherwise, there would be much higher seepage levels even in areas where no gas seepage is observed. Norwest suggested that the restricted connection may be related to the structural hingeline between the coals in the basin versus the outcrop, stratigraphic changes in the coal, coalbed geometry, capillary pressure or relative permeability effects, multi-layer effects, high absorptive capacity in the shallow coals, or other unidentified causes. By modifying the simulated connection of the outcrop to the basin, the model was re-calibrated to match observed gas seepage locations and rates.