The Drilling and Completion of the First Ever Water Disposal Wells in the Middle Gachsaran Formation of Miocene Age, in Abu Dhabi, UAE, Significantly Reduces the Pilot Project OPEX and Associated HSE Risks
Authors: Khan Riaz , Al Dhanhani Helal Ali , Gouda Akl Osama , Abdelaal Atef , Amin Ahmed Mohamed Sameer , Kurniawan Redy , Al Ameri Abdulla 
Published: March 2023

Plan, drill and complete pioneer water disposal wells within the challenging Pilot Project of the complex unconventional reservoir and obtain approval, based on technical justification, of water reinjection within the Gachsaran Formation. This will exclude handling the additional manpower on a daily basis for managing water trucking operations day and night over the remote terrain to the nearby fields (90kms and 110kms). Consequently, this will reduce OPEX and extra liabilities incurred by HSE risks.

The Project included five horizontal producers, completed for the first time within the Middle Gachsaran in the UAE's history. The expected field water production rates were 5000 bbl/d. There was no previous test data available to estimate the injectivity potential of the formation for water disposal. Additionally, no previous approvals were available from the HSE or the risk management team. Available G&G data and subsurface understanding were utilized to best optimize the water disposal wells. Potential reservoir zones were identified based on the good porosities with moderate permeabilities, vertical barriers and their confirmation through MDT pressure measurements, water intake information based on PLT results at nearby vertical wells, and reservoir connectivity. Subsurface and surface locations were finalized as near as possible to the pilot project facility to efficiently inject the water and reduce the CAPEX without compromising the subsurface targets and well integrity. The reservoir monitoring plan for the project was established to monitor any chance of vertical percolation of waste water in the shallow aquifer to avoid contamination.

Multiple vertical barriers exist within the Gachsaran Formation with a regional seal that exists at 1850 ftTVDSS. The regional vertical seal exists at around 2000ft above the top of Middle Gachsaran. Therefore, there was rarely any chance that the injected water would communicate with the shallow formations. In brief, no vertical communication has been confirmed so far across the Gachsaran Formation within the Project Area based on the existence of vertical barriers (anhydrite beds-seals) and results of the formation pressure acquired at several wells and well test data in the area. The reservoir monitoring plan will allow us to overcome any possible chances of cross flow through cement behind the casing of the water disposal well to avoid shallow aquifer contamination. HSEIA / HSE (Safety) Case / HSE Studies Regulatory approval was successfully acquired.

A test case to ensure the Middle Gachsaran as a water disposal candidate within the area. The reinjecting of produced water will save tremendous OPEX for full field development. This will create opportunities for new exploration blocks within this area to allow water disposal produced from deeper reservoirs. Consequently, we provide an attractive economic option to the overseas companies exploring deeper targets within this area.