A parametric study on the benefits of drilling horizontal and multilateral wells in coalbed methane reservoirs

Recent years have witnessed a renewed interest in development of coalbed methane (CBM) reservoirs. The success stories in San Juan basin and other CBM horizons have triggered this renewed interest. Many operators are asking questions regarding the most optimum way of producing CBM reservoirs. Drilling horizontal and multi-lateral wells are gaining popularity in many different coalbed reservoirs with varying results. This study concentrates on many variations of horizontal and multi-lateral wells and their potential benefits. It has been the rule of thumb that vertical wells are appropriate for thicker CBM reservoirs such as those found in San Juan basin and horizontal and multi-lateral wells should be used in thinner beds. Recently some operators are drilling horizontal and multi-laterals even in thicker beds and are claiming economic success. In this study, we identify the most appropriate drilling patterns for coalbed methane reservoirs of different thickness and with different characteristics. The reservoir characteristics that have been studied include gas content, permeability, and desorption characteristics. The yard-stick for comparing different drilling configurations in this study is the net present value (NPV). This way cost of drilling has been taken into account when different horizontal and multi-lateral configurations are compared with one another. Furthermore, we have compared dual-, tri- and quad- laterals with fish-bone (also known as pinnate) configurations. In these configurations, the total length of horizontal wells as well as the spacing between laterals (SBL) has been studied.