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Jul 10, 2012Keywords:
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Main Article Content
Theoretical Basis for Slurry Computation and Compounding in Highly Deviated Wells Cementing
Abstract
Highly deviated oil and gas wellbores offer higher recovery and productivities than vertical wells. But achieving cement slurry stability and accurate volume in vertical wells is not as critical as in deviated wells chiefly because of the large overburden pressure resting on the slurry in deviated wells, among other reasons. Good slurry performance would require the use of appropriately calculated slurry volume and cement materials and additives that can optimize simultaneously the placement and mechanical properties of set cement. In most cases today, slurry volumes in deviated wells are based on rule-of-thumb and utilization of local enlargement factors. In this case, successful job is judged based on slurry returns obtained at the surface. Furthermore, slurry strength is compromised due to excessive overburden and massive casing weight acting at an angle. It is therefore necessary to search for a more appropriate slurry recipe to mitigate slurry failure due to excessive overburden pressure, casing weight and inadequate slurry volume.
This paper presents a to derivation of accurate area and volume ratio equations based on well deviation to calculate appropriate slurry volumes and suggests an idealized slurry systems in deviated sections of the well based on point masses to explore an appropriate slurry recipe to achieve high slurry integrity.
Results show that angle of deviation is very critical to correct cement slurry volume computation for deviated wells. There is a non-linear relationship between cross-sectional area, volume ratio and angle of deviation. As the angle tends to 900, the volume of slurry required increases compared to an equivalent volume required for an equivalent true vertical depth of a vertical well. Furthermore, particle point mass analysis shows that unequal cement particle size distribution would help to create slurry stability through reduction in interstitial water required thus sustain slurry integrity.
