Accurate estimation of hydraulic fracture geometry depends to a substantial degree on precise information about the pressure within the fracture itself. The most accurate means of obtaining this measurement is via instrumentation located at or near the fracture injection point. In modern horizontal completions, this type of measurement is generally considered too expensive or logistically impractical. An alternate approach is to directly measure pressure and pump rate on the surface, and to then computationally account for the fluid friction contributions of each component in the wellbore to deduce the bottomhole fracture pressure. One particular source of uncertainty in this calculation is the contribution of the ball seat stack in a sliding-sleeve completion system. Lab testing of ball seat friction contribution is difficult to obtain, highly subjective and not typically available for a specific installation on-site. Fracture geometry is, therefore, more often than not inaccurately estimated or simply ignored, contributing to inefficient stimulation and consequently resulting in lower production for oil and gas projects.
This paper provides a background basis for traditional bottomhole pressure estimation and its shortcomings in the presence of modern sliding-sleeve completion systems. It then derives a modified form of the rate step-down entry friction test to identify the friction contribution of a sliding-sleeve completion system on-site in real-time and suggests a practical method for execution of this test on a well site.