A Parametric Study and Economic Evaluation of Drilling Patterns in Deep, Thick CBM Reservoirs

Abstract

Abstract Over the past decade, production from unconventional reservoirs such as coalbed methane has increased dramatically. The focal driving force for this growth in coalbed methane production was the development and promulgation of reservoir engineering and completion technology. There have been many studies performed on the well configuration and production optimization techniques in the coal seams. According to many of these studies horizontal, deviated and multi lateral wells are of more benefit compared to the vertical wells. However, the target of these studies has mostly been the thin coal seams hence this result might not hold for the thick CBM reservoirs. The experience has proved that one thick coal is better than an equivalent thickness of multiple thin coals. Samples of the deep thickest accumulation of coal in the world can be found in some of the areas of the United States such as Uintah basin and Piceance basin in Colorado, Black Warrior basin in Alabama and Arkoma basin in Oklahoma and Alaska. The thickness of coal beds in these areas can reach up to 150 ft and they can be as deep as 9000 ft. Although horizontal drilling will result in higher gas production and consequently more revenue, the drilling cost in these wells are significantly higher than the vertical wells. When the coal beds are thick enough that the contact of wellbore and formation is not a limiting issue, the practicality of drilling horizontally versus multiple vertical wells might be questioned. In this work, the most appropriate drilling patterns in thick and deep CBM reservoirs have been identified. A sensitivity analysis has been performed with the intention of addressing the effect of different reservoir parameters and well configurations germane to methane production from CBM. These characteristics include fracture permeability, fracture porosity, gas content, and desorption time. The yardstick for comparing the economical practicality of different drilling configurations under diverse reservoir properties is the Net Present Value (NPV).