Study On Two-stage Cementing Technology

Multi-stage cementing technology is usually used to address or mitigate thecementing problems associated with long hole section, low formation pressure reservoir,and serious lost circulation situation. Cementing becomes more and more difficult withincreasing in the number of complex wells. Even a combination of multi-stagecementing and other technologies is needed to solve the cementing problems ofhorizontal well within the unconventional oil and gas reservoir.This work is aim to analyze multi-stage cementing in a comprehensive mannerbased on previous studies, including cementing tools, technological process, calculationof parameters, technology application, etc. Considered the factors of flowing pressure,weightlessness, inclination, reservoir characteristics, pore pressure and formationfracture pressure, the equilibrium equation of cementing is modified and a model isdeveloped to estimate the appropriate position for the stage-cementing collar. Acementing slurry mixing test is conducted based on the theory of rotational viscometery,and a low mixing energy model is established. It is obvious that enhancing mixedenergy can improve the rheological properties of slurry flowing at low shear rate.Considered effect of reservoir characteristic, reducing the additional differentialpressure in the equilibrium equation of cementing of the premise of stabilizingformation is suggested. The paper calculated the reasonable position of stage-cementingcollar for yan-488well and predicted centralizer position and the pressure changeduring cementing slurry is flowing. The results show that stage-cementing collarposition span is reasonable. By applying multi-stage cementing solutions to some wellswithin complex reservoir, selection of reasonable position for stage-cementing collardoes not only depend on common method, but on annular clearance, additionaldifferential pressure and borehole fluid performance, etc. The cementing performance ofyan-488and yan-491are calculated and analyzed. The results show that the smaller theannular gap is, the lower the position of stage-cementing collar is and the narrower thespan is; the higher the additional differential pressure is, the lower the position ofstage-cementing collar is. The cementing of the horizontal well Hua pu5-39iscalculated and analyzed, it is shown that the reasonable depth of stage-cementing collaris785m, and the additional differential pressure is thought to be the low value due to itslow formation pressure. Therefore, this paper is supplement and improvement on multi-stage cementing technology, it is helpful not only for the technologies applied inwell cementing within complex formation pressure reservoir, but also for the technologyapplied in horizontal wells within unconventional reservoir.