- freely available
Sustainability 2019, 11(23), 6861; https://doi.org/10.3390/su11236861
2. Literature Review
3. Development of Leakage Scenarios
- The last casing shoe was set at 1000 ft (304.8 m).
- Casing diameter was 22 inches (0.56 m).
- Liner hanger diameter was 18 inches (0.46 m).
- Temperature was 100 °F (37.7 °C).
- Four permeability values of 0.01, 0.1, 0.3, and 0.5 mD.
- Faulty elastomers in the liner hanger.
4. Experimental Methodology
5. Results and Discussion
5.1. Experimental Results
5.2. Leakage Scenarios
6. Summary, Conclusions, and Recommendations
- A simple but effective methodology was proposed to estimate the leak time through a casing–liner overlap.
- The developed leakage scenarios showed that the leakage time increases as the length of the casing–liner overlap increases.
- The cement sheath sealability plays a critical role in maintaining the well integrity. The results showed that as the cement permeability increases, the leakage time decreases.
- The leakage scenario results revealed that 62% of the total leakage time falls under the casing–liner overlap range between 50 and 250 ft. This overlap range may not permit a longer duration for the detection and control of gas influx, when the cement sheath is faulty.
- The leakage scenario results suggest that only 35% of the leakage times are between 1 and 30 min. The current casing pressure test duration of 30 min may not be enough to verify the integrity of the cement sheath in the liner hanger overlap.
- It is recommended that the pressure test duration is increased beyond 30 min, depending on the cement column length in the casing–liner overlap. As shown from Figure 6, Figure 7, Figure 8, Figure 9 and Figure 10, the dashed-red horizontal line (which represents 90 min) is the proposed pressure test duration for a cement column length ≥300 ft in the casing–liner overlap.
- It is recommended that the cement column in the casing–liner overlap is not less than 300 ft. The leakage times for all the differential pressure values in Figure 10 are less than 1 h for a 50-ft to 200-ft overlap. Shorter overlaps (50 to 200 ft) can be beneficial because pressure tests may quickly identify leaks if the cement and elastomer in the liner hanger are faulty. Cost may also be a contributing factor for the use of shorter overlaps. However, the leakage scenarios suggest that shorter overlaps have shorter leakage times, which implies a shorter time for gas migration through a faulty cement and elastomer in the overlap. To err on the side of caution, particularly in gas zones, the light-blue shaded area in Figure 10. represents the proposed cement column length in the casing–liner overlap (300 to 500 ft). This proposed range shows longer leakage times for a gas kick to migrate to the end of the overlap. In practice, the increase in leakage time can translate to a longer duration required for the detection and control of gas influx and migration.
- The experiments performed in this study were not at high temperatures. It is recommended that future experimental setups should consider the high temperature effect.
- The analytical method did not account for the cement’s mechanical properties. It is recommended that numerical methods are applied to compensate for the limitations of the analytical method.
Conflicts of Interest
|∇P||Pressure gradient in Pa/m|
|µ||Viscosity of fluid in Pa s|
|A||Cross sectional area of the cement plug in m2|
|Am||Flow area in m2|
|BSEE||The Bureau of Safety and Environmental Enforcement|
|DAQ||Data acquisition system|
|ẟR||Microannulus gap in m|
|GOM||Gulf of Mexico|
|h||Fracture aperture in m (Equation (3))|
|h||Hydraulic aperture in m (Equation (4))|
|k||Cement permeability in m2|
|L||Length of the cement column in m|
|M||Gas molecular weight in kg/mole|
|NVR||Network video recorder|
|θ||Inclination of well corresponding the cement plug in (°)|
|P&A||Plug and abandonment|
|Pd||Downstream pressure in Pa|
|Pu||Upstream pressure in Pa|
|psi||Pound per square inch|
|psia||Pound per square inch absolute|
|psig||Pound per square inch gauge|
|Q||Flow rate in m3/sec|
|R||Universal gas constant in m3 Pa/mole K|
|Rc||Outer casing radius in m|
|Ri||Inner casing radius in m|
|Rm||Microannulus radius in m|
|SCP||Sustained casing pressure|
|t||Leakage time in s|
|T||Temperature in Kelvin|
|W||Fracture width in m|
|W/C||Water to cement ratio|
|WOC||Wait on cement|
|z||Gas compressibility factor|
|α||Fracture orientation in (°)|
|ΔP||Pressure difference across the cement in Pa|
|ρ||Fluid density in kg/m3|
|ω||Length of hydraulic aperture in m|
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