In this Case Study, AFS reviews the remediation and mitigation of asphaltenes on a producing deepwater Gulf of Mexico (GOM) black oil well. This overview summary is based on the presentation “Lessons Learned in Asphaltene Mitigation/Remediation” originally presented by AFS staff at the GOM Deepwater Technical Symposium.
Asphaltenes were a known concern based on previous experience with other wells producing in the same area. The oil had a measured asphaltene onset pressure (AOP) of 4,400 psi and a bubble point of 2,300 psi. During steady-state production, the differential pressure (DP) between the bottomhole and wellhead was increasing.
AFS completed hydraulic modeling to help quantify the amount of asphaltene deposit and potential growth rate of deposition. The modeling results are presented in Table 1.
Table 1. Modeled differential pressure for various restriction IDs and deposit length
|Deposit Day||Restriction Length (ft)||Pipe ID (in)||Overall Friction Loss (psi)||Calculated Volume of Asphaltenes (bbl)|
Solvent soaks of various volumes were completed to establish an optimized remediation protocol for the removal of asphaltene deposits in the wellbore. The performance of the well was monitored before and after the soaks to understand the impact of each remediation. After several soaks, asphaltene deposition was determined to occur as the fluid passed through the AOP (4,400 psi). Additional ASIST studies were conducted to understand how the Gas to Oil Ratio (GOR) was impacting asphaltene instability. Finally, the asphaltene inhibitors were swapped and compared to untreated DP increase to understand the effectiveness at preventing deposition.
Figure 1. Asphaltene inhibitors slow deposition rate, but are unable to completely stop deposition
ASIST modeling indicated a GOR change of only 50 scf/bbl could alleviate the asphaltene deposition issue. Producing wells from the same zone with lower GORs indicated no issues, validating the model. Fortunately, the GOR of the well was declining naturally, indicating asphaltene deposition for this well may be less problematic in the future. A remediation protocol was established to minimize cost and downtime for asphaltene remediation.
The lessons learned on this project that could be applied to future developments are as follows:
- Better assessment of the asphaltene stability issue are required to understand when and where asphaltene deposition is most likely to occur.
- While chemical inhibitors may slow deposition, they are not always effective at eliminating it completely. The availability of a solvent delivery system, including a dedicated umbilical tube, is essential to optimize remediation efforts.