Petroleum Explorationists Offer Strategies to Unlock More Oil Barrels from Mature Fields

Peter Uzoho

As Nigerian oil and gas operators grapple with mature fields, declining reserves and tight drilling budgets, the Nigerian Association of Petroleum Explorationists (NAPE) has urged them to learn from the ND Western’s experience on the Utor-40 well in Utorogu Field in Oil Mining Lease (OML) 34 in Delta State.

NAPE said the Utorogu Field offers a compelling case for integrated subsurface evaluation and real-time drilling intelligence over rigid adherence to Field Development Plans (FDPs) submitted to the Nigerian Upstream Petroleum Regulatory Commission (NUPRC).

A member of NAPE and Head of Geoscience at ND Western, Dr. Christopher Asuquo-Jackson gave the advice when he presented the case study at the association’s September technical/business meeting in Lagos on the theme: “Leveraging Integrated Subsurface Evaluation and Real-Time Drilling Intelligence to Maximise Reservoir Value and Optimise Well Delivery: A Case Study of Utor-40 Well drilling, Utorogu Field, OML-34.”

Utorogu is a historically gas-prone asset in the Western Niger Delta, part of OML 34 operated under a Joint Venture (JV) arrangement with the Nigerian National Petroleum Company Exploration & Production Limited (NEPL) where ND Western serves as the operator.

Like many onshore assets divested by the international oil companies (IOCs), the challenge is not finding hydrocarbons but maximising value from thin, stacked, and often saturated reservoirs that were bypassed in earlier development phases.

According to Asuquo-Jackson, ND Western initially planned to complete Utor-40 as a single horizontal string targeting the E14 reservoir, with a forecast of 2,000 barrels of oil per day.

But he said the plan changed after the pilot hole was drilled and tested, penetrating nine hydrocarbon-bearing reservoirs, opening a window to re-evaluate the original completion strategy using petrology, petrophysics, reservoir engineering and live drilling data.

“The initial rate was supposed to be a maximum of 2,000 barrels per day. That was the forecast and the plan that we had. So, on drilling the pilot hole, we’ve tested about nine hydrocarbon-bearing reservoirs,” Asuquo-Jackson said.

Instead of staying with the single-zone plan, he said the integrated team identified an additional saturated reservoir with a primary gas cap and an oil column that could be co-developed, leading ND Western to opting to revise the completion to add the second zone.

“We were able to achieve about 2,000 stock-tank barrels for the original plan reservoir, which is the E14 reservoir. Now the additional reservoir is a saturated reservoir with a primary gas cap. So, we planned to complete and add that, and we were able to add additional 300 barrels per day of rate to the original plan,” he explained.

According to him, the 300 bopd uplift pushed total delivery to over 2,000 bopd, with minimal incremental completion cost.

For marginal field operators where every barrel counts to cover evacuation and security costs, such gains are material.

For the wider Nigerian upstream oil and gas industry, where over 60 per cent of production comes from mature assets and FDPs are often treated as sacrosanct, he said the lesson for explorationists was threefold, including collaboration, real–time drilling intelligence, and flexibility and dynamism with the FDPs.

“You know, we actually run an integrated system, not just a particular discipline. So we are running from geoscience to reservoir engineering to drilling engineering to economics to completions,” Asuquo-Jackson said.