Model Helps Guide Choke-Management Strategies Under Constraints

Abstract

This article, written by JPT Technology Editor Chris Carpenter, contains highlights of paper SPE 187190, “Choke Management Under Wellbore, Completion, and Reservoir Constraints,” by Emmanouil Karantinos, SPE, and Mukul M. Sharma, SPE, The University of Texas at Austin, prepared for the 2017 SPE Annual Technical Conference and Exhibition, San Antonio, Texas, USA, 9–11 October. The paper has not been peer reviewed. Choke-management strategies vary significantly among operators. No rigorous methodology exists for properly selecting choke sizes when constraints are placed on completions, wellbores, and fluid pressures and velocities. In this paper, the authors propose a coupled wellbore/reservoir model that performs dynamic nodal analysis using integrated models for surface-facilities, wellbore, and reservoir simulators and allows an operator to select choke sizes as a function of time. Introduction The suggested algorithm consists of three primary entities: the reservoir, the wellbore, and the completion. A reservoir simulator provides the rate as a function of drawdown or bottomhole pressure (BHP), and a wellbore model is used to calculate the frictional pressure loss along the wellbore and the surface flowlines. Depending on the fluid system, the appropriate choke-flow model is used. Dynamic (time-dependent) nodal analysis ensures the continuity of pressure and rates between the wellbore and reservoir entities at every timestep. The algorithm suggests the maximum available choke that satisfies, at all times, the entire set of user- specified constraints. The complete paper applies the method to two scenarios. The first is a high-permeability, vertical casedhole well in which screen erosion is a serious concern. For that particular case, the choke sizes should be adjusted to limit perforation velocities under the critical threshold of 10 ft/sec, which has been shown to cause screen erosion in high-permeability offshore wells. The authors show that choke sizing depends on various parameters, including the separator pressure, the well trajectory, and the true vertical depth. Finally, the method is applied to the design of a flowback operation in order to prevent proppant flowback and proppant crush-ing in a hydraulically fractured unconventional well. Design Considerations To mitigate the risk of productivity impairment or failures associated with the completion or other equipment, production engineers should take into consideration existing guidelines for allowable values of flow velocities or drawdown limits. These recommendations can be classified into three major categories: wellbore, completion, and reservoir constraints. Wellbore constraints include, but are not limited to, the maximum pressure drop across the choke to prevent hydrate or wax and asphaltene formation downstream of the choke, the maximum fluid velocity in the surface flowlines to prevent erosion, and the minimum fluid velocity along the wellbore trajectory to ensure effective proppant transport during flowback operations. Completion and reservoir constraints depend on the completion type in place. Table 1 of the complete paper presents several completion and reservoir constraints along with their maximum allowable values reported in the literature.