This paper addresses some challenges concerning cement slurry designs, focused on thickening time, requiring careful engineering practices, and proper cementing operational considerations. It presents a series of thickening time test studies compared to "conventional testing practice" versus "field simulated testing" to illustrate the differences between results.
Many aspects of oilfield cementing are sufficiently important to warrant study. One area that requires attention is the procedures used to design the cement slurry in the well. The batch-mix and static conditions influence the physical attributes of oilfield cement, including thickening time. Conventional laboratory testing invariably follows the API procedure for thickening time. Although this might be adequate in most cases, it may only precisely predict field behavior (at actual conditions) in some cases.
Conventional thickening time tests may not necessarily indicate the true responsiveness of cement slurry. Traditional thickening time waiting periods do not relate directly to how long a slurry can remain static and still be moveable after an inadvertent or intentional shutdown during placement. Mixing, pumping, and displacing the cement (including any shutdown) affect the hydration and thickening behavior. Therefore, it is imperative to understand the relative contributions from each part of the process toward the thickening time to help prevent failures. These contributions might not significantly impact slurry properties but should be quantified and understood. The reliable prediction of cement thickening time can be vital to the success of oilfield cementing operations. Because cement placement techniques have become complex, delivering slurry with accurate thickening time can be crucial to the job's success.
This paper presents a modified testing protocol to evaluate the effects of batch-mixing and static-period on cement slurry's thickening time to minimize the incidents related to the premature setting of cement slurry.