As you can see from the front cover of this month's issue of Global Cement Magazine, we have launched the first-ever Well Cem Conference and Exhibition on well cements, which will take place on 13 - 14 January 2014 in Dubai. The conference will concentrate on cement production and cement performance in place. I thought that it might be useful to give a recap on the basics of well cement (including cement for oil, gas, water and geothermal wells) for prospective attendees. Technology has come a long way since Frank Hill of the Union Oil Co. first mixed and dumped 50 sacks of cement into a well to shut off water flow in a Californian oil well in 1903.
Well cement production
Well cements are modified portland cements, which have been produced to tight chemical and mineralogical specifications and which have particular properties tailored to down-hole requirements of high temperature and pressure, and long service life under aggressive chemical attack. The American Petroleum Institute (API) operates a specification and certification process which is followed by the vast majority of well cement producers and which specifies the particular composition and properties of the produced cement. The API specification includes eight grades of cement from A to H. Classes G and H are the most widely used oilwell cements and offer moderate-to-high sulphate resistance. The ISO 10426 standard may additionally be applied to oilwell cement.
Stringent testing and analysis (including XRD, XRF, PSD and strength testing) is required for all well cements. Around 130 cement plants around the world have API oilwell certification, including plants owned by Holcim, Lafarge, Lehigh, Italcementi and Dyckerhoff. These plants represent only around 6% of all of the world's cement plants1 but oilwell cement demands a premium price and higher margins than other types of cement.
Cement companies usually sell direct to cementing companies, although well cement can also be purchased from traders including Interbulk (owned by Italcementi), HC Trading and others.
Cement slurry properties
The well cement, once mixed with additives and water to produce a pumpable slurry, must have a number of properties such as: 'predictable thickening time (set time), high sulphate resistance, high durability, fluid loss control, consistency, low viscosity, low free fluid, and strength.'2
A wide variety of additives can be used to modify and control cement slurry properties, including bentonite, carbonates, diatomite, metakaolin, mica, perlite, silica flour, sodium silicates, glass bubbles, high-specification gypsum and various types of organic-based chemicals.
The cement, water and additives are mixed together in high speed, high specification mixers at the surface and are then pumped into place by cementing contractors. Among the largest cementing contractors in the world are Schlumberger, Halliburton, Saipem, Transocean, Baker Hughes, Weatherford International and Trican. These companies typically provide cementation as one of a range of oilfield services. Thousands of other companies offer cementation services.
Well cements are used to cement a pipe into place down a drill hole, making sure that there is no free space between the pipe and hole that would otherwise allow drilling fluids, water, gas or oil to migrate up the outside of the drill casing. The cement also provides structural integrity to the hole. The cement is pumped down the inside of the well casing from the surface, and flows from the end of the casing and back up the outside of the casing into the annulus between the casing and the hole, where it solidifies under the high temperatures and pressures found at depth.
Well cement properties are extensively tested and are more critical than for non-well cement performance. Premature thickening can have disastrous consequences due to loss of circulation in the well. Thickening times that are too long can cause financial losses due to excessive Wait-On-Cement (WOC) times between drilling periods.2 After the residual cement and any plug has been drilled out of the casing following thickening and setting, a logging company will send a probe down the hole to ensure that the cementation job was effective. An effective cementation job is critical to the success of the well, as the infamous failure of the Macondo well showed.
With strong industry backing already, the Well Cem conference in Dubai should be a fascinating event and a terrific place to do business. See you there!
1: Global Cement Directory 2013
2: http://www.lafarge-na.com/Related_download_1_Specialty_Oil_Well_slide_43.pdf