A Note on Well Cementing at Low Temperatures

Abstract

In October 1945. R. F. Farris, in an AIME paper entitled "Method ForDetermining Minimum Waiting on Cement Time," presented a method forcalculating the minimum WOC* time required in oil well cementing operations.Briefly, this method consisted of shutting in a well after the cement had beenplaced, and noting the time required for the wellhead pressure to reach amaximum. This time was then multiplied by a factor of 1.5 to determine when thecement had reached sufficient strength to support the weight of thecasing. As a result of this work, a number of areas have reduced their WOC timerequirements with the subsequent saving of considerable rig time. The tests conducted by Farris were for the most part, conducted under cementingtemperatures in excess of 70'F. This was done because in the overwhelmingmajority of cases, cementing temperatures are in excess of 70'F (only in thenorthern part of the country, primarily in the Rocky Mountain area, incementing surface casing are temperatures below 70'F. encountered, and suchtemperatures occur only during the winter months). The Stanolind ResearchLaboratory since that time has performed a number of tests both in thelaboratory and in the field to evaluate this WOC factor when cementingtemperatures are lower than 70'F. The results of these tests indicated theneed for greater WOC time in areas affected by abnormally low cementingtemperatures. These tests indicated that a WOC factor of 2 (Time from start tomix cement to maximum wellhead pressure x 2 = Time to drill plug) will allowsufficient time for the cement to develop adequate strength. A field test under abnormally low cementing temperatures (surface temperature35'F, mud discharge temperature <70'F, and cementing depth 500'Ft.) in theRangely Field, Colorado, using the WOC factor of 2, indicated the time to drillthe plug as 45 hours. Well conditions preventing getting back into the welluntil a 48-hour WOC time had elapsed. At this time, the plug drilled firm tohard indicating that the cement had reached its final set. It is contemplated that during next winter additional field tests will beperformed to further check the results of the laboratory and field testsconducted to date. *WOC, abbreviation for "waiting on cement", indicates the time from when thecement is mixed to the time when sufficient strength has been obtained to allowthe drilling of the plug.