Abstract
Deep-Water Disposal wells (DWD) project started in 1996 to process excess water output in in deep aquifers (Lower Mehwais) in South Oman D field. As saving environment is increasingly becoming part of the companies’ core business, the threat of DWD to environment, in general, and to groundwater, in particular has been raised by the government. Therefore, a new policy has been set by the government to close all DWD by 2026 or reclassify them as water injectors if they have a clear impact on field pressure and production performance.
D field has 2 DWD Wells close to it, despite the drop in water injection in the field, pressure remains almost constant which was the trigger to for this study. This paper summarizes the technical subsurface work done to understand the communication between the producing and disposal formations. This is mainly to ensure the amount disposed water is maintained with time and consideration is given to them as a source of pressure support, to manage them in an improved manner and safeguard volumes. The procedures followed to quantify the support from DWD wells to field D:
Analyze field production and pressure data incorporated with operational observations.
Use analytical techniques like MBAL model to demonstrate the effect of DWD on historical pressure match.
Use numerical methods describing DWD effect, sector dynamic model.
Incorporate results from other technical studies like PTA analysis.
Overview of the technical studies describing DWD effects (MBAL and Sector
Model work, PTA).
Conduct economic analysis on multiple cases of DWD scenarios (cost vs. Benefit).
Integrate the outcomes from this study between surface and subsurface teams to ensure this reclassification percentage is reflected in waterflood KPI compliance and monitoring.
Looking to the historical pressure data, field D pressure data increase is in parallel with start of Deep-water disposal wells (DWD). In addition, Clear decline in oil production was observed in 2017 when DWD injection reduced by 20%. Which explain that the DWD has impact on production. Multiple scenarios with different percentage of DWD contribution was tested in MBAL model to assess pressure response for Field D. Results indicated a pressure support between 20-25 %. This fraction is consistent with history match results from sector dynamic model. From the Economic scenario results, continue disposal water injection in field D is the most attractive scenario economically as it reduces the UTC from 26.8 to 0.2 $/bbl and increases NPV by 20 $ mln compared to drilling new water injectors. Maintaining the injection rate on nearby DWDs at maximum of 15,000 m3/d is crucial to safeguard HW NFA forecast.
To reflect this reclassification project, multiple teams need to integrate (subsurface, surface and operations) and collaboration with EC, EDM, SAP, Nibras and OFM database should be implemented. This 20% percent of contribution should be used for any field performance parameters calculation such as VRR, HCPVI, Throughput and monitoring operating envelope and compliance purposes. Which is incorporates in multiple visual waterflood management tools.
