A novel bypass downlink system for casing sliding sleeve and its laboratory verification

Abstract

The widely accepted hydraulic fracturing technology in the unconventional oil/gas exploitation needs an effective way to open and close the casing sliding sleeve in order to save cost and avoid the unnecessary risk of the downhole operations. We propose a novel downlink system using downhole pressure waves to remotely control the opening and close of the casing sliding sleeve from the surface. We develop a laboratory device to understand the characteristics of the downhole pressure waves. According to the laboratory experiments, we find that the changing of the wellbore pressure can be described by an exponential expression when the cased wellbore is either closed or leaked. There are three parameters in the expression, including the steady-state high pressure (PH), the steady-state low pressure (PL), and the system constant (τ0) of pressure increasing and decreasing. Both PH and PL are a function of the wellbore leakage volume and the τ0 is a function of both the wellbore volume and the leakage volume. In addition, due to the strong attenuation of the high-frequency component (>10 Hz) of the pressure wave resulting from the long distance propagation in the wellbore channel, we use the baseband transmission to send the codes from the surface to the casing sliding sleeves by opening and closing the bypass valve. We also proposed a float matching decoding method to overcome the inaccuracy and inefficiency of the existing baseband transmission method. The novel codec method is validated by the laboratory experiments and the results indicate that the float matching decode can effectively improve the accuracy and efficiency of baseband transmission with a relatively short length of code under the situation of the strong noise and well leakage.