Confidential Shell documents disclosed in a United Kingdom court case have revealed ageing pipelines, hundreds of unaccounted-for oil wells and an estimated $10.9bn decommissioning liability, intensifying scrutiny of the company’s environmental legacy in Nigeria’s Niger Delta.

The disclosures are contained in Nigeria: Lifting the Lid, a report published by Amnesty International and seven environmental and human rights organisations. The report analyses internal Shell emails, technical audits, presentations and reviews released during ongoing litigation in UK courts.

The rights groups allege that Shell was aware of serious integrity failures in its pipelines and oil wells, exempted its Nigerian subsidiary from some internal safety standards and delayed decommissioning ageing infrastructure despite acknowledging the environmental risks.

The report comes about a year after Shell completed the sale of its former onshore subsidiary, Shell Petroleum Development Company, to Renaissance Africa Energy, a transaction that attracted concerns over responsibility for decades of oil pollution in the Niger Delta.

Among the most significant disclosures is an internal email describing the ageing Nembe Creek Trunk Line as “a basket” because of its deteriorating condition.

The 96.5-kilometre pipeline, one of Shell’s major crude evacuation routes with a capacity of about 150,000 barrels per day, had long been plagued by leaks, vandalism and crude oil theft.

According to the report, although Shell replaced the pipeline in 2010, about 80 kilometres of the old line remained filled with stagnant crude oil because the company allegedly lacked funds to decommission it properly.

The documents indicate that the abandoned pipeline recorded at least six operational oil spills after its replacement, while internal communications warned that further spills were inevitable unless urgent action was taken.

The report also alleges that Shell continued oil production despite recognising the environmental dangers posed by the deteriorating infrastructure.

It further claims that the company could not account for hundreds of oil wells in its Nigerian operations.

According to the report, an internal assessment submitted to Shell’s then Chief Executive in 2014 showed that hundreds of onshore wells were either missing from the company’s electronic tracking system or their condition could not be verified.

The documents indicate that Shell subsequently launched a “well hunt campaign”, which identified about 750 overdue maintenance tasks.

The report also alleges that Shell lacked real-time pipeline monitoring systems capable of detecting smaller leaks before they caused significant environmental damage.

It says technical reviews found that pipelines designed to be replaced every 15 years remained in operation well beyond their intended lifespan, with maintenance relying largely on repairs after failures rather than preventive replacement.

The report further claims that more than 1,600 pipeline clamps had been installed across Shell’s network, including numerous older clamps whose exact locations could no longer be identified.

Amnesty International argues that the internal documents also challenge Shell’s longstanding position that most oil spills in the Niger Delta were caused by sabotage, crude oil theft and illegal refining.

According to the report, senior Shell officials acknowledged that illegal tapping points were at times left on pipelines because removing them would require shutting down production.

One internal communication cited in the report alleged that security personnel responsible for pipeline protection accused Shell of being “complicit” in oil theft because illegal connections were not promptly removed.

The report also claims some Shell executives suspected that certain company staff and contractors were involved in organised crude oil theft.

One of the report’s most significant financial disclosures is an internal estimate placing the cost of decommissioning Shell’s onshore assets at $10.9bn, excluding environmental remediation.

Another internal presentation reportedly identified about 375 square kilometres of polluted mangrove forest and questioned whether the company had the “appetite” to address the open-ended environmental liability.

The rights groups argued that Shell’s divestment should not absolve it of responsibility for pollution accumulated during decades of oil production.

Director of Amnesty International Nigeria, Isa Sanusi, said the documents undermined years of public assurances by the oil giant.

“Shell has long blamed oil theft and sabotage for pollution in the Niger Delta. But these documents cut through years of denial and raise grave questions about what Shell knew, what it allowed to continue, and whether it then sought to walk away from the costs of its toxic legacy,” he said.

Chairman of HEDA Resource Centre, Olanrewaju Suraju, said affected communities deserved “truth, justice, clean-up and full remedy” after decades of environmental degradation.

The coalition of organisations called on the Federal Government to strengthen regulation of the petroleum industry, conduct comprehensive audits of ageing oil infrastructure and establish a dedicated Niger Delta environmental clean-up fund.

Responding to the report before its publication, Shell rejected the allegations.

“The characterisation and portrayal of Shell in your letter is not one we recognise,” the company said.

“Shell is committed to honesty, integrity and respect for people, and to conducting business in an ethical and transparent manner.”

The company added that the allegations did not reflect the “challenging operating environment in the Niger Delta” during the period covered by the documents.