* Many high-cost projects unnecessary if climate targets met
* More than a third of Exxon, Shell budgets seen at risk by 2025
* Graphic: Projected oil and gas capex (reut.rs/2sSAMe0) (Shell reaction, graphic)
By Ron Bousso
LONDON, June 21 (Reuters) - Energy giants including Exxon Mobil and Royal Dutch Shell risk wasting more than a third of their budgets on projects that will not be needed if climate targets are to be met, a thinktank report shows.
More than $2 trillion of planned investment in oil and gas projects by 2025 could be redundant if governments stick to targets to lower carbon emissions to limit global warming to 2 degrees Celsius, according to a report by the Carbon Tracker thinktank and institutional investors.
It compared the carbon intensity of oil and gas projects planned by 69 companies with requirements needed to meet the warming target set by the 2015 Paris agreement, which will require curbing fossil fuel consumption.
It found Exxon, the world's top publicly-traded oil and gas company, risks wasting up to half its budget on new fields that will not be needed.
Shell and France's Total would see up to 40 percent of their budgets misspent.
Fossil fuel producers have come under growing pressure from investors to reduce carbon emissions and increase transparency over future investment.
Sweden's largest national pension fund, AP7, one of the authors of the report, said last week it had wound down investments in six companies, including Exxon, which it said had violated the Paris agreement.
Top energy companies have voiced support for the Paris agreement reached by nearly 200 countries. Many of them have urged governments to impose a tax on carbon emissions to support cleaner sources of energy such as gas.
U.S. President Donald Trump said this month he would withdraw the United States from the Paris accord which he said would undermine the U.S. economy.
The report found five of the most expensive projects, including the extension of Kazakhstan's giant Kashagan field and Bonga Southwest and Bonga North in Nigeria, will not be needed if the global warming target is to be met.
Around two thirds of the potential oil and gas production which would be surplus to requirement is controlled by the private sector, "demonstrating how the risk is skewed towards listed companies rather than national oil companies", the report said.
Saudi Arabia's state-run Aramco, widely considered the lowest cost oil producer, would see up to 10 percent of its production rendered uneconomical, the report said.
The report's authors said their discussions with oil companies had shown the companies wanted to remain flexible to respond to future developments and possible changes in the oil price.
Companies including Shell and BP have rejected the idea that assets could end up redundant, saying the reserves they hold are too small to be affected by any long-term decline in demand.
"We believe our business strategy is resilient to the energy transition. We are convinced there is a role for gas to help with the transition to a lower carbon world," Shell said in response to the report.
Reporting by Ron Bousso; editing by Adrian Croft and Jason Neely