Halliburton has successfully delivered its first lightweight cementing solution for Shell West of Shetland. The 13" inch casing on the South Uist well (214/21a-2) west of Shetland, was cemented using Halliburton's low density Tuned Light slurry in which an integral part of the formulation was 3M Glass Bubbles.
"Using Tuned Light ultra-light weight cement was determined to be the optimum solution for the 17½ inch sections of this well," explained David Kulakofsky, Halliburton's global cementing champion. "For this particular job we needed a lightweight slurry and using the 3M Glass Bubbles provided us the capability to design the low density that the wellbore conditions required."
Primary cementing is an important operation in the construction of any oil well. The casing is cemented in to the borehole by pumping cement down the inside of the casing and back up the annulus. The main objectives of cementing operations are to provide zonal isolation to prevent fluid migration in the annulus, support the casing and protect the casing from corrosive fluids.
"Cement slurries are often designed with a lead and tail," explained Kulakofsky. "Typically a lead slurry will be around 12.5 pounds per gallon (ppg), with a 16ppg tail. The 12.5ppg lead provides the required height of fill. While the slurry has low strength, the weight is light so it doesn't add too much extra stress on the casing or formation. The tail slurry is typically designed at 16ppg as this gives sufficient strength to tack the shoe in place and support to drill through and enter the next hole section."
For this South Uist well equivalent circulating density (ECD) calculations showed that conventional 12.5 lead cement was too heavy and could potentially fracture the wellbore. The ECD calculations suggested that a 10.5ppg cement was required. If mixing a conventional cement is attempted at 10.5ppg the set properties, if any, would typically be below minimum acceptable ranges. One benefit of the 3M Glass Bubbles is they allow for the creation of lightweight slurries with the set mechanical properties similar to conventional slurries mixed at their traditional densities.
Moira Peck, a senior technical professional at Halliburton Cementing, said,"The slurries, therefore, needed to be specifically formulated for the downhole conditions in the particular well." Peck makes the point that these cements (slurries) are, therefore, chemically quite sophisticated.
In fact, the cementing of the 20 inch section of the South Uist well was done using Halliburton's ZoneSeal isolation process for foam cement, but Peck explains that this technique wasn't used for the 17½ inch section partly because the logistics for using Tuned Light cement were less complex and required fewer personnel than foam cementing.
"With the foam product we needed an eight-man team and kit on the deck of the rig. With the Tuned Light cement, it was effectively a standard cement job that could be handled by the existing team. As well as easing the pressure on bed space - always an issue offshore - we were able to use a regular crew and less equipment."
Arthur Evertson, the production chemist - cementing for Shell said, "So for Shell it was a good choice to use the Tuned Light Blend for this section."
The use of 3M Glass Bubbles had a number of advantages, suggested Darren Hall, 3M's oil and gas technical sales manager. "Apart from their high strength and low weight, they have very low shrinkage, which enhances the cement formulation. The bubbles are easy to handle and are chemically benign. This makes handling and blending them very easy.
"Our 3M microspheres can be used in cement slurries with densities as low as 7ppg. One of the advantages of using the product is the consistent quality of the bubbles. Because they are a non-porous engineered product they are easy to formulate and therefore produce consistent and stable slurry properties."
Peck concluded by saying that Shell is always willing to work with contractors to develop the use of new technologies. "Tuned Light cement with the 3M Glass Bubbles was just one of several advanced technologies, including Halliburton’s SSR-II Plug System, that we used to successfully deliver this well," she said. "With a flow area that is 75 per cent larger than conventional plugs, the SSR-II system improves fluid flow and reduces pressure drop through the plug set – and allows the mechanism to sustain higher flow rates for longer times without damage. They represent a significant advancement in subsea release mechanisms to ensure successful outcomes at offshore cementing jobs."
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