Investigering av skumsements oppførsel og foradring i logge respons fra tidlig til sen fase.

Abstract

Cementing an oil and gas well can pose significant challenges, particularly due to the static and dynamic pressures exerted by the heavy cement slurry when circulated into the wellbore. A narrow operational window for mud weight between the collapse pressure and fracture gradient of the well, often requires special cement designs where density can be lowered but still provide a good annular bond. Foamed cement is one of the cement designs that offers the ability to adjust downhole density to help mitigate a potential well fracture, and at the same time provides the necessary annular cement to obtain a good annular bond. In the Greater Ekofisk Area (GEA), current operator ConocoPhillips Norway (CoPNo) has successfully utilized foamed cement for over two decades. However, assessing foamed cement logs in the early stages after hardening can be challenging. Interestingly, these logs appear to exhibit improved acoustic properties over time. This thesis aims to explore one potential explanation for this phenomenon: the pore structure within the foamed cement becomes filled with formation water (H2O) over time.

Through laboratory testing utilizing an Ultrasonic Cement Analyzer (UCA) machine, this thesis aims to uncover differences in transit time (TT) between foamed cement samples flooded with either Nitrogen (N2) gas or H2O. In theory the water-flooded sample should exhibit lower TT readings, as water is a better conductor of soundwaves compared to N2 gas. The results of the laboratory tests confirmed this theory, revealing a significant difference in TT readings between the two mediums and indications of weak signals arriving from the N2 gas flooded sample. Furthermore, upon converting the TT readings to acoustic impedance (AI), it was found that the N2 gas flooded sample exhibited a reduction in AI of approximately 60% compared to the H2O flooded sample.

The findings align with the hypothesis that pores flooded with H2O within foamed cement will decrease TT readings compared to pores flooded with N2 gas, consequently increasing the AI of the foamed cement. In other words, H2O filled pores within foamed cement provide a plausible explanation for the observed improvement in foamed cement logs over time. Further research is needed to definitively confirm this explanation and sensitivity tests should be conducted to explore variations in wellbore temperatures experienced across the entire cemented interval.

Cementing an oil and gas well can pose significant challenges, particularly due to the static and dynamic pressures exerted by the heavy cement slurry when circulated into the wellbore. A narrow operational window for mud weight between the collapse pressure and fracture gradient of the well, often requires special cement designs where density can be lowered but still provide a good annular bond. Foamed cement is one of the cement designs that offers the ability to adjust downhole density to help mitigate a potential well fracture, and at the same time provides the necessary annular cement to obtain a good annular bond. In the Greater Ekofisk Area (GEA), current operator ConocoPhillips Norway (CoPNo) has successfully utilized foamed cement for over two decades. However, assessing foamed cement logs in the early stages after hardening can be challenging. Interestingly, these logs appear to exhibit improved acoustic properties over time. This thesis aims to explore one potential explanation for this phenomenon: the pore structure within the foamed cement becomes filled with formation water (H2O) over time.

Through laboratory testing utilizing an Ultrasonic Cement Analyzer (UCA) machine, this thesis aims to uncover differences in transit time (TT) between foamed cement samples flooded with either Nitrogen (N2) gas or H2O. In theory the water-flooded sample should exhibit lower TT readings, as water is a better conductor of soundwaves compared to N2 gas. The results of the laboratory tests confirmed this theory, revealing a significant difference in TT readings between the two mediums and indications of weak signals arriving from the N2 gas flooded sample. Furthermore, upon converting the TT readings to acoustic impedance (AI), it was found that the N2 gas flooded sample exhibited a reduction in AI of approximately 60% compared to the H2O flooded sample.

The findings align with the hypothesis that pores flooded with H2O within foamed cement will decrease TT readings compared to pores flooded with N2 gas, consequently increasing the AI of the foamed cement. In other words, H2O filled pores within foamed cement provide a plausible explanation for the observed improvement in foamed cement logs over time. Further research is needed to definitively confirm this explanation and sensitivity tests should be conducted to explore variations in wellbore temperatures experienced across the entire cemented interval.