Mohammed Shaibani, Fatma Shehhi and Uzma Ghulam of Petroleum Development Oman outline the effort in their paper, “Reviving a Dormant Opportunity: The Mabrouk Deep Gas Discovery,” which they will present this month at AAPG’s International Convention and Exhibition in Istanbul, Turkey.
The Mabrouk field in northern Oman was discovered in 1980. After the initial discovery well, two deep wells, Mabrouk-4 and 12, targeted the deeper Barik and Miqrat reservoirs of the Haima Supergroup – the same formations that are producing in the main gas fields to the east.
Flow rates were considered non-commercial and the effort was abandoned.
“With increasing demand for gas in the country, there was always intense activity to look for gas reserves, and Mabrouk was not forgotten as such,” said Ghulam, senior seismic interpreter at PDO.
“Explorationists believed that it had potential, but it was always known to have a problem of poor data quality in the deeper gas reservoirs, so acquiring the latest 3-D seismic over the area was key,” she said. “Due to the high demand, it was agreed to invest money and acquire advanced 3-D seismic over the area, which gave us a reasonably good image at depths of more than four kilometers.”
The area was re-mapped in 2008 and researchers were surprised to realize the earlier wells had been drilled on the flanks of the structure.
“The improved seismic image of the deeper Haima section (Amin reservoir) was a key in the decision to spud a third well in the field,” she said, “as the new map showed that the previous two deep wells were drilled on the extreme flanks of the structural closure, hence the updip potential was identified.”
Exceeding Expectations
Mabrouk-32 was drilled in 2012, about five kilometers updip of Mabrouk-4 and both Barik and Miqrat sandstones as fully gas-bearing with good reservoir properties, the authors state.
They write in their abstract:
“Given the potential size of the structure, covering approximately 60 square kilometers, it was decided to immediately drill an appraisal well to assess the field’s potential. Thus the appraisal well Mabrouk-35 was drilled down flank to confirm gas-water contacts.
“The results came in as expected, confirming the presence of almost three TCF of gas-in-place, making it one of the biggest gas discoveries in the Sultanate of Oman in the past decade.”
The Barik and Miqrat reservoirs in Mabrouk-32 were hydraulically fractured and tested in late 2012 – and the well exceeded expectations.
“For Mabrouk-32, it took only 10 months to drill a deep exploration well, test it and then get it connected to the production system – the fastest hook-up for an exploration well in Oman,” Ghulam said. “This was despite the remoteness of the well and gas evacuation pipelines, and the fact that the delivery and installation lead times often exceed one year.”
Almost one TCF had been booked at the end of 2012, and the initial development of the field is expected to address about 40 percent of this volume.
“The Mabrouk field is also a producing gas and oil field from shallower reservoirs, hence it has well developed pipelines and production facilities that could be utilized for the gas produced from the deeper Haima Group reservoirs (Barik and Miqrat),” she said.
“The biggest lesson learned was that a good quality dataset is the biggest asset an O&G business can have, and decisions based on unreliable data will always be questionable,” Ghulam said.
“In highly explored and mature basins like that of interior Oman, the Mabrouk discovery has renewed our hopes, and this has triggered various new 3-D WAZ seismic and 4-D seismic acquisitions, which are currently ongoing,” she said.
The Mabrouk field has been classified as a stranded gas opportunity, and regional scaled projects looking at all similar opportunities also are currently ongoing.
“Such a successful outcome,” Ghulam said, “requires a lot of effort and precise planning from various departments and disciplines.”