| Abstract |
Potter Drilling, Inc. has developed an approach to improve productivity of wells by creating vertical slots in the wellbore wall using their thermal spallation technology. The majority of impedance in a productive well often occurs in the near-wellbore region due to the restriction of fluid flow within the immediate vicinity (several inches to a few feet) of the borehole walls. Reasons for this near-wellbore impedance can be related to “non-darcy” flow, formation damage from drilling or injection of fluids, reduction in permeability due to precipitation of minerals during production, or other types of skin effects (such as incomplete penetration). This paper presents the results of our analysis and threedimensional numerical modeling, where we evaluated what impact the creation of slots in the wellbore wall could have on a well’s productivity from various types of geothermal systems. The parameters evaluated during this study included the overall slot dimensions (length and width), number and orientation of slots relative to fracture orientation, initial flow characteristics of the wellbore region (low, intermediate, and high permeabilitythickness values), along with flow rate and the effect of a large negative skin factor. In addition, various types of flow regimes were studied including flow in a porous medium, near-horizontal fractures and near-vertical fractures. Initial results from these modeling studies suggest that by changing the geometry of the wellbore through the creation of controlled slots, a well’s productivity index can be increased significantly, the typical increase being on the order of 100%. It was found that a well’s production rate and power capacity will not necessarily increase in proportion to the increase in PI due to slotting because of the pump constraints for pumped wells and wellbore pressure-drop constraints for self-flowing wells. In pumped wells, the power- capacity increase by slotting will depend not only on the slotting effectiveness in increasing productivity index, but also of various wellbore-specific parameters, such as fluid temperature and pump characteristics for marginally commercial wells; the overall increase in power capacity would typically be between 50% and 100% due to pump constraints. In self-flowing wells, the power-capacity increase due to a 100% increase in productivity index by slotting will yield a 25% to 100% increase in well power capacity given the wellbore flow constraints. |