Horizontal wells have brought significant improvements in production of unconventional reservoirs. However, one of the main debates in completion optimization lies on the effects of horizontal well geometry throughout a well's life. On the other hand, gas lift installations are becoming widespread to leverage the depletion in pressure and flow rate. Transient multiphase simulation allows physics-based modeling of flow performance in horizontal wells without or with gas lift application. The objective of this work is to use these simulations and provide a qualitative analysis of well geometry effects on slugging and production of horizontal wells.
This study uses OLGATM as a transient multiphase simulator to mimic a horizontal well's production over 36-hour time periods. The well produces through a 2-7/8″ ID tubing with MD of 10000 and TVD ranging from 4900 ft to 5100 ft, depending on the lateral geometry. The lateral section has a deviation angle range of 88-92°, with three geometries simulated, including toe-up, toe-down and horizontal. For each geometry, two cases are simulated: one without any undulations and one with random undulations along the lateral section. A realistic decline curve equation is used to estimate the decline in reservoir pressure throughout the well's life and simulate its production for 6 years, including early life with higher rates and late life of the depleted well. Gas lift is also installed late life to analyze its impacts on flow.
The simulation results offer valuable insight into well geometry effects throughout a well's life. At early life, slugging is minimal and production rates are close for all the geometries, with simulations favoring the toe-up well by a small margin. However, the geometry effects increase significantly as the well depletes. Slugging becomes more severe in almost all toe-up and horizontal cases, causing large fluctuations in pressure and reduction in total production. Undulations in toe-up help reduce the slugging severity and slightly improve the production. Gas lift proves to help reduce the back pressure and slugging severity downstream of the valve, and significantly improve production. The study of well geometry and its impacts on production design remains to be limited. Therefore, this study is a unique effort to provide a guideline and optimize well configuration and artificial lift design.