Over the past decades, environmental regulations for oil and gas companies have become increasingly more stringent to protect and preserve the environment for future generations. This is particularly true for remote areas and environmentally sensitive terrestrial and marine locations where there is a strong emphasis on protecting natural habitats and resources. Accordingly, many regulatory agencies have adopted "zero discharge" policies requiring all generated wastes to be disposed in a responsible manner. For drilling operations, the various waste streams that need to be handled and disposed of properly include: drill cuttings, excess drilling fluid, contaminated rainwater, produced water, scale, produced sand, and even production and cleanup waste. Old practices involve temporary box storage and hauling of the waste products to a final disposal site. Often, these sites are several kilometers (km) away from the generation source, creating not only liabilities for the operating company, but also environmental risks from accidental releases and gas emissions that result in higher operating costs.

To address these concerns, waste management technologies have evolved to offer cuttings re-injection (CRI) as a safe and cost-effective alternative that permits the permanent and contained disposal of drilling cuttings in an engineering-determined subsurface formation. CRI provides a secure operation achieving "zero discharge" by injecting cuttings and associated fluids up to several thousand meters below surface into hydraulically created fractures. This disposal technique mitigates any surface environmental risks and future liabilities for operating companies.

Saudi Aramco has taken the initiative to utilize CRI as the preferred technology to manage drilling wastes that will be generated in the Manifa field development. To minimize risks associated with CRI, and conduct successful injection operations, an Assurance Waste Injection Process was set in place to continuously monitor the operation and plan ahead for any eventuality. Assurance of the injection operation begins during the planning phase with a comprehensive feasibility study based on existing data. Simulations are performed for the anticipated downhole waste domain to ensure containment within the selected formation and permit adequate design of surface facilities for the particular project.

This paper describes the various components of the first Saudi Aramco CRI "pilot" study. These include: reservoir/geomechanical data analysis and interpretation; preliminary geomechanical modeling; target zone selection; test well design, drilling and injectivity testing; and geomechanical model refinement using field injectivity data. The objectives of this study for the Manifa field development project were to evaluate:

  • What are the most promising zones for injection based on the geomechanical model?

  • Do overlying formations provide effective containment of the injected wastes?

  • What are the injection rates, volumes, slurry rheology, and particle size requirements for field testing?

  • What were the results of the field injectivity testing at MNIF-ABC?

  • What are the long-term, predictive results from re-calibration of the geomechanical model?

  • What is the well design and completion strategy during the implementation phase?

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