Well testing system eliminates H2S risk while enabling reliable flowback
A closed-loop testing system was applied to test wells with ultrahigh-H2S content—without release to atmosphere. The system reliably handled the wells without any flow limitations or H2S exposure, meeting the operator's objectives.
Testing ultrahigh-H2S wells often presents technical and HSE risks. Reservoirs with high H2S content can’t be flowed using an industry-standard well test package. For an operator in the Middle East, high H2S conflicted with testing objectives, causing the operator to enforce strict limitations during flowback operations.
A previous attempt to start the flowback required shutting in the well. The operator needed a solution to deliver the well within the highest safety standard guidelines. Additionally, the operator wanted to obtain representative well test data and prepare the well for production.
SLB proposed a full closed-loop testing system that eliminated the need to open valves for sampling. The closed loop prevents gas from bleeding into the atmosphere and enables operations to be performed in ultrahigh-H2S environments. Through advanced engineering, the unique well testing system was put in place to more reliably flow back the well with improved well performance and to meet all safety requirements for ultrasour conditions.
The design involved specialized operating procedures created for the project to ensure safer equipment handling and sampling. Through project design studies, SLB proved the necessity of considering the equipment’s material class. Thus, API Spec 6A EE-NL material class was selected as suitable to handle ultrasour wells. Other third parties were unable to provide the material class and match the required safety design standards to mitigate H2S exposure.
The closed-loop testing system ensured that neither the environment nor the personnel experienced H2S exposure. This was made possible by integrating automated equipment and devices in the process, including an innovative technology to measure H2S in real time.
The closed-loop system uses a sampling mechanism where manual samples are collected for further analysis without atmospheric release. The sample is isolated and treated to remove H2S, resulting in a sample free of gas. With the fully automated double-barrier choke manifold, the valves are remotely controlled, and the choke size changes were executed from 50 m away, with none of the crew exposed to H2S and high pressures. The specially designed equipment offers reliable pressure control in a harsh environment and eliminates 100% of the potential gas release during choke changes. An exclusive inline H2S meter was developed to measure multiphase flow in real time. In addition, the Vx Spectra™ surface multiphase flowmeter measures H2S inline continuously, in real time and without manual sampling. The meters increase measurement accuracy and eliminate the need to take samples that would otherwise be released into the atmosphere. The system also includes an inline gas specific gravity measurement to avoid personnel exposure while taking samples, an SIL2-rated electrical emergency shutdown system to increase reliability in operations with the fast-acting safety system, and advanced engineering in process simulations, gas dispersion, and transient wellbore analysis.
Sour wells, which were rarely able to be flowed back, can now be produced safely and reliably with the closed-loop testing system, handling production with ultrahigh H2S content. Nine consecutive flowing days have been achieved so far from a previous 24-h maximum flow period. Well performance proved better than expected.†
The system was applied to six ultrahigh-H2S wells in total and produced without any flow limitations.
† Standard conditions: 14.7 psi at 60 degF
