Understanding Surface Casing Waiting-on-Cement Time

Abstract

The waiting-on-cement time in low-temperature surface casing cementing canvery often be reduced to less than what is common practice today through abetter understanding of cementing conditions. Two major factors in the earlydevelopment of the compressive strength of cement are the water-cement ratioand the curing temperature. The latter is partially dependent upon theformer. The strengths of cements required for drill-out are discussed, and the curing times required to achieve the necessary strengths are presentedgraphically. API Class A, B and C cements are considered, and the advantages of using the densified systems are illustrated. Data from field studies concluded over the past several years, including temperature measurements on well fluids and temperature surveys followingcement jobs, illustrate the curing temperature behaviours of typical western Canadian surface casing cement jobs. The effects caused by heat of hydrationand by cement mixing water and displacement fluids which are warmer than formation temperatures, can be rather significant, producing average curing temperatures which are higher than the surrounding formation temperatures by asmuch as 5°F to 30°F or more. A laboratory study was made to determine the comparative effects of the heatof hydration of cement slurries under different conditions. The heat evolved isincreased when (1) the slurry is placed at a higher starting temperature, (2)the volume of slurry is increased and (3) the slurry is mixed at a higherdensity. Cementing practices are discussed and recommendations made. With a more thorough knowledge of the basic factors involved, it should be possible in manycases, to more accurately correlate the required waiting-on-cement time withthe conditions as they exist rather than adopt a policy of fixed time which satisfies all probable conditions of cementing materials, temperatures and techniques. Introduction The phrase "waiting-on-cement," or "WOC," has long been a misnomer in mostinstances. The nonproductive and expensive time spent waiting has usually notbeen necessary, because, in fact, the cement was firmly set and was actuallywaiting on us. Increasing concern is being expressed by the industry over thiscostly waste, and continual attempts are being made to reduce WOC time to asafe minimum. The area of greatest interest appears to be that of surfacecasing cementing; this is due to the difficulties caused by the lowertemperature curing conditions.

Effect of Perlite Particles on Barite Cement Properties

“…The time to achieve a compressive strength of 500 psi for the slurries is presented in Table . This is the wait-on-cement time, which indicates the time allowed for the cement to set and develop sufficient strength to support the casing before drilling out the casing shoe . This time could vary from hours to days depending on various conditions such as field practice and depth of cement placement. , The addition of 3% perlite powder to the barite slurry resulted in a general reduction in WOC time.…”

Wpływ drobnoziarnistej krzemionki na parametr czasu oczekiwania na cement – WOC

“…W branży naftowej przyjęte jest, że minimalna wartość wczesnej wytrzymałości na ściskanie, po której uzyskaniu możliwe jest przystąpienie do dalszych prac po wykonaniu zabiegu cementowania, wynosi wspomniane 3,5 MPa i wartość tę określa się mianem WOC (z ang. waiting on cement) (Maier, 1965).…”