Schlumberger

Case Study: Integrated Sub-Surface Assurance Technology Applied Successfully in Demanding Caspian Injection Project

Challenge: The Caspian Sea is a geologically complex and highly environmentally regimented environment, which is particularly challenging when engineering a subsurface waste injection (WI) project. Azeri M-I Drilling Fluids, Ltd. (a joint-venture between M-I SWACO and Azerbaijan National Oil Company SOCAR) was first awarded a contract in 2005 for delivering waste injection services throughout the Caspian Sea. Each production and drilling platform was intended to have a dedicated well and WI systems to process and inject drilling waste. Successful operation of WI was so crucial for overall field development that its failure was recognized as one of top 10 risks to achieving the full field production targets of 1 million bbl/day. The complexity of intended disposal zones, represented primarily by massive mudstones, regional faulting and tectonic activity was complicated further by the lack of prior WI experience in the targeted sector. The targeted area mandated deep sub-surface engineering design and vigilant monitoring of sub-surface waste disposal domain.

Solution: Based on drilling plans and available geological and geophysical data, the M-I SWACO WI Sub-Surface Group in Houston developed a set of engineering studies, lab tests, field trials and processes to address sub-surface challenges of the project including:

  • Geological, geophysical and drilling data evaluation
  • Geomechanical model and fracture simulations
  • Injection well and equipment requirements
  • Slurry lab test with actual cuttings samples
  • Continuous pressure monitoring and analysis
  • Continuous model calibration and disposal fractures dimensions resolution

Result: Successful cooperation between the M-I SWACO WI Sub-Surface Group and operational teams, along with the operator’s recognition and cooperation, resulted in a successful engineered approach to all aspects of the subsurface injection operation. The methodology employed allowed for risk identification and mitigation while enhancing safety and operational performance. The calibration to actual injection pressure response and hydraulic fracture simulations on the specialized TerraFracTM 3D software resulted in maximum achievable disposal fracture dimensions as well as contingency injection zones. Solids disposal capacities have been identified based on formation stress increase calculations. To date, more than 1.9 million bbl of drilling waste have been injected successfully into four dedicated injection wells on four platforms with zero NPT related to the injection process. The proactive approach and experienced personnel of the M I SWACO WI Sub-Surface team successfully integrated the sub-surface challenges into a continuous solution process, amplifying the sub-surface safety and performance of the pioneering WI project in the Caspian Sea.

Summary

For each injection well a geo-mechanical model reflecting mechanical properties of injection and overburden formations was built. Further, slurry lab tests with actual cuttings and water samples were performed to identify the optimal slurry properties, such as density, viscosity, rheology and viscosifying requirements. Maximum allowable static times were defined to avoid solids settling and wellbore plugging.

As a final step, a continuous injections monitoring process was established to serve as connection point between injection field operations, the operator and the M-I SWACO Sub-Surface team. The successful proactive identification and mitigation of risks was a function of data recording, reporting, pressure analysis, hydraulic fracture modeling, regular meetings and presentations to the operator teams, and close involvement of field operations in creating and updating operational procedures.

For instance, signatures of restricted fracture entry were detected on the injection pressure behavior of one of the wells. Simultaneously, a fast injection pressure increase was observed, which could lead to reaching the pressure limits prematurely.

Quick analysis concluded that restriction could be induced by cuttings accumulated near wellbore. An enhanced over-flush injection with increasing rate and a higher viscous pill/ seawater volume was recommended and pumped successfully, meeting the intended objectives. Accordingly, injection pressure returned to the intended rate.


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