2nd Global Well Cem Conference & Exhibiiton 2015
22 - 23 January 2015, Houston, Texas
The 2nd Global Well Cem Conference has taken place successfully in Houston, Texas, USA, with over 100 delegates from 18 countries in attendance. Attendees praised the conference for its high technical content and strong networking opportunities. The 3rd Global Well Cem Conference will take place in London in 2018.
(Above: winners of the Best Presentation Awards (l to r) Jo Harder, Dr Vipu and Timon Echt).
View the image gallery from the 2nd Well Cem Conference & Exhibition 2015 (large gallery - may take time to load)
The second Global Well Cem Conference took place in Houston, the centre of the world's oil industry, at an interesting time: The price of oil had more than halved from its high point and stood at US$46/barrel on the first day of the event. Oil companies and oil service companies had started to announce job cuts in the industry around the world. One delegate said that prospects for the industry in the North Sea were 'dismal.'
Joe Harder of OneStone Consulting started the conference by commenting on the effects of the drop in oil prices on the oil industry and on the oil well cement industry. "Low oil prices are not sustainable in the long term. Oil production will be cut in the long term and oil prices will recover quite soon to US$100/barrel, within a year." Joe said that the amount of oil well cement used per well is from 75t to 360t, depending on well length, well type, drilling parameters, cementing practices and safety factors. Globally there will be a 6% decline in oil wells drilled in 2015, but there will be 640,000 wells drilled between now and 2020. Global demand for oil well cement is around 11Mt/yr, but will increase to 13.7Mt/yr by 2020. The Americas account for 63% of wells drilled, but only 54% of oil well cement demand. Other regions now have a higher potential for growth than the Americas. Joe reminded the audience that the transportation costs of oil well cement are a major factor in the high price, easily exceeding the material costs. The low C3A content of oil well cement is the main difference between it and OPC. It also requires higher burning temperatures. Higher consistency and quality control is required for oil well cement (OWC), leading to higher production costs. There are only three large markets in the world where continuous OWC production is possible using a small kiln of 600-1000t/day: USA, China and Russia. All other markets require batch production to be economic.
Shawn Adams of the American Petroleum Institute (API), one of the founder sponsors of the Global Well Cem Conference, next asked and answered his own question, 'Why API?' Shawn reminded delegates that it is the members of the global oil industry who actually write the standards that effectively control operations in the industry, through an API-organised collaborative process (including the API Winter Meeting, which immediately followed the Global Well Cem Conference), which the API then packages up and sells to its members and subscribers. The API Monogram Programme was established in 1924 and is now used by around 5000 companies in 70 different countries. The main API programme of relevance to oil well cement is API Spec 10A on oil well cements. In total 76 companies have been licensed to API Spec 10A, with many in China.
Hugh Wang of Cemex USA next spoke on the potential implications of specifications on oil well cement slurry formulations. "Cement is only one of the ingredients in oil well cement slurries and the quality parameters of oil well cement are tested without reference to the other ingredients," he said. "You have to have very good alite crystals in terms of size and morphology, you must have very low free lime, without over-burning the clinker and you need very low C3A content." Hugh highlighted some differences between API and ASTM oil well cement specifications. ASTM has a lower fineness limit and has adopted a performance-based specification for the content of SO3, allowing higher SO3 content as long as the cement does not exceed a specific expansion level. This can be important to allow the use of supplementary cementitious materials and additives. The two standards also differ in their approach to the calculation of mineral phases. Hugh pointed out the importance of there being sufficient SO3 content in the cement paste, to allow the conversion of problematic expansion-prone ettringite into mono-sulphate. He pointed out that the addition of gypsum to the slurry can improve the rheological properties and consistency of the cement paste, but added that the gypsum mineralogy must also be well-controlled. Over-calcined gypsum can include a proportion of anhydrite, which has very different properties from alpha and beta hemi-hydrate. Too much SO3 in the cement will lead to the formation of secondary gypsum, which will lead to false-setting behaviour.
Johann Plank of the Technical University of Munich next spoke about the early hydration of oil well cement under zero gravity conditions. Professor Plank reminded listeners that needle-shaped hexagonal crystals of ettringite are formed in a flash precipitation - in less than a second - when cement is mixed with water. These crystals of ettringite are responsible for the early strength development of cement. Admixtures work by anchoring to the surface of ettringite crystals in the cement paste and by modifying crystal behaviour. Johann described a series of experiments conducted on an Airbus flying parabolic 'zero-g' flights. Each experiment was conducted by pumping water into a cement sample with a syringe at the start of the zero-g period, allowing a reaction for 10 seconds, and then removing the water with the syringe and stopping the reaction by adding acetone with another syringe. An API-certified oil well cement from Dyckerhoff was used. It was found that the crystal size, aspect ratio and quantity of crystallites were comparable at 1g and at zero-g. In zero-g there is no convection and so the mechanism for transport of ions to the crystal surface is solely through the action of diffusion (although the zero-g experiments were obliged to also use vigorous shaking to accomplish mixing of ingredients). With the addition of a super-plasticiser in the experiments, there was a tendency towards fewer and smaller ettringite crystals.
Ashok Santra of Weatherford International next spoke on the effects of silica addition on fluid loss control. Challenges to additive performance come from cement variations, temperature and pressure conditions, water quality (and salt content in particular), particle size distribution, slurry density, rheology, other additives and the action of SCMs - and cement slurry performance must also be achieved at the lowest possible cost. Fluid loss happens when the slurry loses fluid in a porous formation, causing incomplete cement hydration. This can lead to premature gelation, problems with circulation, poor bonding of the filter cake and channel formation and possible gas migration. In the standard fluid loss test machine, if there is a 'blow out,' the entirety of the fluid will be lost from the sample, whereas other samples will lose their fluid more slowly and this can be controlled with the use of loss control additives.
Fluid loss control additives have evolved over the years and the state-of-the-art is now synthetic polymers - the higher the molecular weight of the polymer, the higher the effectiveness in controlling fluid loss (but in turn having more of an effect on slurry rheology). The additive works by tying up water molecules through hydrogen bonding, through film formation and through plugging pores. Ashoka mentioned AMPS-NNDMA, an additive that is salt tolerant up to 18%bwoc (by weight of cement), which is stable at higher temperatures and which is viscosifying in nature, which delays static gel strength development and which can shorten the transition time. The additive is relatively tolerant of other additives, including dispersants and retarders. Ashok pointed out that cementers are seeking the shortest possible transition time, where the cement slurry passes through the gel-phase before it becomes a solid and during which time it is at its most gas permeable. Crystalline silica is used to counter strength loss at higher temperatures. However, addition of high levels of silica can make the slurry too viscous to be pumpable. This can lead to fluid loss problems meaning that the use of dispersants is required. However, this can, in turn, lead to reduced effectiveness of the fluid loss additive. The use of very fine grained silica fume or even nano-silica can reduce the fluid loss effects while retaining the strength effects of silica. A combination of polymers seems to be the best approach to fluid loss in the presence of silica.
Chuck Alt of Kerneos next spoke about the use of calcium aluminate (CA) cements for well bore cementing. The basis for production of CA cements is a complete fusion or sintering through melting of the raw mix, rather than the usual clinkerisation of OPC. CA cements have rapid-hardening properties, which have found numerous civil engineering uses. They are also strongly exothermic, allowing them to be used in low temperature environments. The cements also withstand high levels of sea water exposure and application at high temperatures. CA cements also react with a wide variety of other minerals such as limestone, gypsum, nitrates, chlorides, bromides, fumed silica, ground granulated blast furnace slag (GGBFS) and metakaolin, to form new mineral families. Chuck said that CA cement can be used to alter the performance of OPC, partly through the promotion of ettringite formation, leading to high early strength development. However, CA cement can be prone to 'conversion,' which is an inevitable transition of early-formed meta-stable hydrate. At temperatures of 30°C and higher, this transforms into a long-term stable hydrate, which has a lower strength: Conversion should be promoted or forced to occur to achieve the true long-term strength as soon as possible after placement. Chuck spoke about Ciment Fondu, Secar 71 and about 'Cement X' CA cements, which all have specialised characteristics, which can add particular properties to oil well cements and which can be used to make custom cements that have finely-tuned setting times and strength gain curves.
Heiko Plack of Dyckerhoff next spoke on the possibilities and potential difficulties of making consistent oil well cement. Heiko defined consistency as 'little variation' of physical and application-relevant performance criteria, which may be achieved via a high level of quality control, but also through an effective feedback loop from customers. For oil well cement, strength development and rheology are prime parameters. However, consistency is also vitally important, due to the assumption that a lower level of cement variation during production will lead to a lower variation of slurry performance in the field. Heiko pointed out that if the cement plant cannot produce oil well cement clinker in a continuous mode (the best approach for reducing variation in cement characteristics) and has to produce in batch mode, then the longer the production run in each batch, the lower the likely variation in cement characteristics. The dedication of facilities to oil well cement production, such as kiln, mills and silos, will further lead to decreased variability in product characteristics. Heiko concluded that perhaps the most important requirement for producing a consistent oil well cement is a special know-how on how to produce the material, supported by experience and a clear long-term commitment to oil well cement production as a core business. "Newcomers often underestimate the extent and magnitude of the required production infrastructure and know-how for production of a consistent oilwell cement," he said.
Professor Cumaraswamy Vipulanandan, also known as Vipu, next spoke on the use of 'smart cement' for real-time monitoring for deep water oil well cements. Vipu said that the two inches of cement that might surround the casing is asked to do a lot - and is sometimes asked to do too much. He pointed out that once the cement is pumped down the hole, there are very few ways of determining its performance: Has it solidified? Has there been fluid loss? Has there been channelling? Are there problems with degradation or with corrosion? "So many questions and so few answers!" he exclaimed. More than 40% of the failures of wells in the US (at a rate now of around 1 in 400 wells) is due to a failure of the cementing job. Vipu wants to use the entire cement as a sensor, as opposed to burying sensors in the cement, with the cement being used as a piezo-chemi-resistivity sensor akin to human skin, based on alternating current resistivity measurements. It was shown that resistivity changes dramatically with cracking, with contamination of the cement slurry with drilling mud and with the age of cement. Deciphering the meaning of the resistivity measurement and sending the information back to the surface are just two of the many hurdles that will need to be surmounted for the approach to work.
On the evening of the first day of the conference, delegates enjoyed a memorable night out at a cowboy ranch, being serenaded by a pair of cowboys and eating typical Texan fare of beans and brisket, washed down with local Shiner Bock beer.
On the second day of the conference, Gilles Numkam and Andrew Meaux of Louisiana State University spoke about the application of micro-indentation tests in the evaluation of well cement integrity, specifically to avoid micro-annulus gas migration. The presenters seek to use indentation hardness testing as an alternative non-destructive test method for compressive strength measurement. It was shown that the values are correlated, albeit imperfectly.
Timon Echt of the Technical University of Munich next spoke on the impact of pressure and temperature on the hydration kinetics of oil well cement. Temperature rises on average by around 1.3°C per 100m of depth, although it can be much higher in geologically-active areas. Timon investigated the effects of temperatures up to 120°C and pressures up to 550bar on the thickening time and hence the pumpability of cement slurries. Silicon magic angle spinning NMR, AAS, XRD and SEM were used to examine test samples. There were strong decreases in hydration times with increasing temperature, but only small decreases with increasing pressure. There was almost no change in hydration duration above 80°C due to pressure. The influence of pressure up to 280bar was significant on hydration time, but was small compared to temperature effects. However, at lower temperatures, the effect of increasing pressure was much higher. It was suggested that there is a strong pressure-dependent increase in Al3+ ions in pore solutions and that this promotes increased formation of ettringite and earlier setting of cement.
George Quercia of Trican Well Service next spoke about the application of Weibull statistics to tensile testing for oil well cement compositions. George stated that the ideal cement has a lower Youngs Modulus than average, a similar compressive strength, higher elastic deformation (ductility) and is tough - able to absorb fracture energy. It was found that the minimum number of samples that needed to be tested for tensile stress, to achieve a 95% confidence level in the result, was 24 when using the familiar 'dog bone' tensile strength test, but was an even higher number when using the Brazilian test. Standard tests with only five samples have a confidence level approximately 15% lower than those with at least 24 samples.
Karen Luke, also of Trican Well Service, next spoke about the correlation between porosity measurement and conductivity of set oil well cements. Porosity is determined by the degree of hydration, the water to cement ratio and the volume of paste. Porosity can be correlated to compressive strength, flexural strength and permeability. Accurate determination of the porosity of cement is not a trivial matter. Karen said that the resistivity of a sample is very much easier to measure and, in conjunction with standard porosity measurements, an attempt was made to correlate the two measurement approaches. Resistivity is a function of cement microstructure, including pore volume, pore size distribution, pore radii and soluble salt content. Karen outlined the experimental set-up for resistivity measurement, which also turns out to not be perfectly trivial to measure. However, it was determined that for two of the tested cement compositions of 'normal' density, class G well cement and Thermal cement, that there was a strong correlation between resistivity and porosity: However, for a lightweight cement including flyash and hollow glass spheres there was very little correlation, possibly due to the crushing of the glass spheres due to applied pressures during testing.
In the final presentation of the conference, Peter Boul of Halliburton spoke about the activation of a strongly retarded Portland cement slurry. Peter spoke about the mechanisms of retardation of a variety of additives, including organic phosphonates, phosphates, borates, saccharides and lignosulphonates, which act through calcium complexation, through direct surface adsorption of the retarder onto the clinker phase, through nucleation poisoning and/or precipitation of a semi-permeable layer onto cement grains. In his experimental results Peter showed that different oil well cements had remarkably different responses to retarder additives.
There was a lively discussion at the end of the programme, regarding the allocation of risk between cement producer and cement user, about the near-impossibility of knowing the performance of the cement at the bottom of the hole and about the difficulties of predicting the interactivity of different additives with each other and the cement slurry in all the conditions likely to be found 'down-hole.'
At the end of the conference, prizes were awarded for the best presentations, as voted-for by the attendees. Joe Harder of OneStone Consulting was third and Timon Echt of TU Munich was second, but Vipu was awarded first prize for his enthusiastically-presented paper on smart cements for down-hole cement performance determination.
Delegates rated the conference highly for its technical content and for its many effective networking opportunities, as well as for its eclectic mix of participants from the global cement and well cementing industries.
The 3rd Global Well Cem Conference will take place in London in 2018.