Natural Gas

Billions of cubic meters

Natural gas’s share of the global energy market has been growing unabated for more than 30 years. Gas and oil producers have developed the simplest, cheapest fields. In coming decades, however, they will have to contend with fields containing increasingly sour or acid gas. Some 40% of the world’s remaining gas reserves are sour or acid, with about 10 billion cubic meters containing more than 10% hydrogen sulfide (H₂S) and at least 20 billion cubic meters containing more than 10% carbon dioxide (CO₂). These compounds corrode facilities and require the use of materials that can withstand them. And since hydrogen sulfide gas is fatal to humans even in very small doses, safety must be iron-clad. Removing sour and acid components from gas requires innovative sweetening processes that balance efficiency with cost effectiveness. The residues left over from their production must also be managed in a sustainable, environmentally respectful way.

Long-established leadership

In the 1950s, Total became the first oil company ever to take up the challenge of developing very sour gas, when we began developing the immense Lacq field in southwestern France, whose gas contained 16% hydrogen sulfide and 10% carbon dioxide. In this extraordinary learning laboratory, we developed techniques and materials to produce and sweeten this corrosive gas safely.

The first sweetening unit was installed in 1957 and was based on the use of a chemical molecule known as DEA*, from the amine family. When in contact with raw gas, DEA reacts quickly with the hydrogen sulfide and carbon dioxide and strips out the acid compounds. Sixty years of sustained innovation have continuously improved the process, its performance and energy efficiency, while lowering its cost. That is how we developed MDEA*, a selective amine designed to eliminate hydrogen sulfide, followed by activated MDEA*, which can extract some or all of the carbon dioxide.

Our cutting-edge expertise means that we have been awarded contracts to develop more than 60 sour or acid gas fields worldwide, in the United Kingdom, Iran, Thailand, Russia, Norway and the Middle East. For instance, in the Elgin/Franklin field in the U.K. sector of the North Sea UK sector, our “customized” solutions can sweeten gas with variable carbon dioxide and hydrogen sulfide content. The activated MDEA adjusts automatically to variations in the composition of the gas produced and delivers a gas that meets commercial specifications.

More recently, we have developed a hybrid solvent formulation consisting of an amine and a physical solvent. The process, deployed since early 2008 at the Lacq plant, does a better job of stripping the mercaptans from the gas, while also removing the hydrogen sulfide and carbon dioxide.

Taking aim at ultra-sour/acid gas

However, conventional chemical processes alone cannot sweeten very sour or acid gas, a strategic resource that will be needed in the future to ensure the planet’s energy supply. To tackle ultra-sour/acid gas, Total and our partner French Petroleum Institute (IFP) opted to switch from chemical to physical techniques. The resulting disruptive innovation, dubbed Sprex®*, is the product of five years of R&D and is dedicated to gases with very high hydrogen sulfide contents. It was followed by Sprex® CO₂, for gas with high carbon dioxide concentrations. Both work on the same principle: the hydrogen sulfide and carbon dioxide are separated from the methane by means of once-through cooling in a system at temperatures as low as -70 °C. Whereas the conventional method converts the hydrogen sulfide to sulfur and releases the carbon dioxide to the air, Sprex® delivers the separated acid fractions in the form of a compressed liquid. This “residue” is then ready to be pumped into a geological reservoir, a solution that meshes perfectly with the environmental responsibility advocated by Total.

Sustainable protection of the environment

Managing the carbon dioxide and hydrogen sulfide effluents that accompany sour or acid gas production in a sustainable, responsible manner is a priority focus of our R&D efforts. Because injecting them into an underground geological storage facility is one of the most environmentally friendly options, Total is investing heavily in this promising solution. Looking for alternatives to the traditional conversion of hydrogen sulfide into sulfur, a permanently saturated market, we are concentrating on hydrogen sulfide injection into depleted reservoirs. The major challenge is assuring the long-term safety of this storage option.

Carbon dioxide is the primary culprit in global warming. We are pursuing a very proactive strategy to significantly and sustainably curb our emissions of this greenhouse gas, notably by investing in highly innovative capture and geological sequestration technologies. An unprecedented commercial pilot is being launched in Lacq, France, in mid-2009, to demonstrate the feasibility of this new technology to counter global warming.