To necessity of gas migration control under well cementing

Well construction and operation is often complicated by the occurrence of formation fluids and their movement through the annulus as a result of poor-quality cementing. It is possible to reduce costs and time for eliminating behind-thecasing and inter-casing flows significantly due to effective preventing of these phenomena. The purpose of the research is to present the analysis results of the factors causing the development of the formation fluid flow channels during cementing as well as to find a solution to the problem of well annulus flows. The research involved the examination of the mechanisms of the processes occurring under cement slurry evolution in the well annuluses under well-casing, existing methods for solving the problem of formation fluid migration, as well as the ways to prevent them. The authors propose a method preventing the formation of migration channels, which they think is the most promising to eliminate the adverse effects of the named problem. To implement the method, the operation principle of the OFITE laboratory installation is analyzed as well as the modeling method for cement slurry borehole conditions. The graphs obtained as a result of cement tests and their interpretation are given. It has been determined that in most cases cement systems not modified by appropriate reagents are not able to restrain fluid migration during the transition from liquid to solid state. Moreover, fluid migration occurs during a critical period under cement setting after 3–8 hours of hardening. As a result of the work carried out, it was revealed that the chosen method of evaluating and modifying of cement systems makes it possible to increase the potential for an effective solution of the problem of formation fluid migration by decreasing the probability of behind-the-casing flow formation.

gas migration, transition time, cementing, annulus, behind-the-casing flows, well-casing, oil-well cement, intercasing pressure