Influence of the contact time of the preflush fluid with the filter cake on the effectiveness of the purification of the annular spaceIn the process of drilling wells, tightness in the annular space between casing string and beyond is of particular importance. In order to eliminate undesirable gas migration due to lack of tightness, lowered casing string should be sealed by filling the annular space with cement slurry. During the pumping of cement slurry, drilling mud is removed from the annular space. However, cement slurry pumped directly after the mud, cannot sufficient remove residues from the mud. In order to properly seal the borehole with cement slurry, which after binding is designed to prevent the flow of gas, it is necessary to clean the annular space from filter cake by pumping the preflush fluid, and then completely removing the mud by spacer fluid and cement slurry. Fulfilling these conditions and obtaining a properly cleaned annular space prior to cementation can help improve the sealing and to some extent eliminate the possibility of undesirable gas migration at the contact of the cement sheath with the contact surfaces (casing string and rock formation). Taking into account the problem of improving the cleaning of the annular space and related issues, the laboratory tests have been carried out to determine the effect of the contact time of the preflushes on the purification of the annular space. During conducting the laboratory tests used the simplest type of preflush fluid, which was water. Such selection was conditioned by the necessity to demonstrate the effect of contact time on the efficiency of cleaning the annular space, excluding the physico-chemical action of the surfactant used in the preflush liquid. In order to pick up changes, control samples were also prepared on which no filter cake was produced. Laboratory tests of the effect of the contact time of the preflush fluid on the purification of the annular space were conducted by determining the adhesion of the cement sheath to the rock formation, from which the previously produced filter cake was removed.Key words: contact time of the preflush fluid, wash fluid, preflush fluid, cleaning of the annular space.Wpływ czasu kontaktu cieczy przemywającej z osadem płuczkowym na skuteczność oczyszczenia przestrzeni pierścieniowej W procesie wiercenia otworów wiertniczych szczególne znaczenie odgrywa zapewnienie szczelności w przestrzeni pierścieniowej pomiędzy kolumnami rur oraz poza nimi. W celu wyeliminowania m.in. niepożądanych zjawisk migracji gazu na skutek braku szczelności należy zapuszczoną kolumnę rur okładzinowych uszczelnić wypełniając przestrzeń pierścienio-wą lub pozarurową zaczynem cementowym. W trakcie tłoczenia zaczynu cementowego z przestrzeni pierścieniowej wypierana jest płuczka. Jednak tłoczony zaczyn cementowy nie jest w stanie dostatecznie dobrze usunąć pozostałości po płuczce. W celu dobrego uszczelnienia otworu zaczynem, który po związaniu ma za zadanie uniemożliwić przepływ gazu konieczne jest dokładne oczyszczenie pr...