The Lacq gas field is a

natural gas field A petroleum reservoir or oil and gas reservoir is a subsurface accumulation of hydrocarbons contained in porous or fractured rock formations. Such reservoirs form when kerogen (ancient plant matter) is created in surrounding rock by the presence ...

located in

Aquitaine Aquitaine ( , , ; oc, Aquitània ; eu, Akitania; Poitevin-Saintongeais: ''Aguiéne''), archaic Guyenne or Guienne ( oc, Guiana), is a historical region of southwestern France and a former administrative region of the country. Since 1 Janu ...

. It was discovered in 1950 and developed by and

Total S.A. TotalEnergies SE is a French multinational integrated energy and petroleum company founded in 1924 and one of the seven supermajor oil companies. Its businesses cover the entire oil and gas chain, from crude oil and natural gas exploration and ...

It began production in 1958 and produces

natural gas Natural gas (also called fossil gas or simply gas) is a naturally occurring mixture of gaseous hydrocarbons consisting primarily of methane in addition to various smaller amounts of other higher alkanes. Low levels of trace gases like carbo ...

and condensates. The total

proven reserves Proven reserves (also called measured reserves, 1P, and reserves) is a measure of fossil fuel energy reserves, such as oil reserves, natural gas reserves, and coal reserves. It is defined as the " antity of energy sources estimated with reasona ...

of the Lacq gas field are around 8.8 trillion cubic feet (251 km³), and production is slated to be around 1 billion cubic feet/day (35×10⁵m³).

Geology

The Lacq Gas Field is a

structural trap In petroleum geology, a trap is a geological structure affecting the reservoir rock and caprock of a petroleum system allowing the accumulation of hydrocarbons in a reservoir. Traps can be of two types: stratigraphic or structural. Structural trap ...

located in an

anticline In structural geology, an anticline is a type of fold that is an arch-like shape and has its oldest beds at its core, whereas a syncline is the inverse of an anticline. A typical anticline is convex up in which the hinge or crest is the ...

which formed in the southern part of

Aquitaine Basin The Aquitaine Basin is the second largest Mesozoic and Cenozoic sedimentary basin in France after the Paris Basin, occupying a large part of the country's southwestern quadrant. Its surface area covers 66,000 km2 onshore. It formed on Varisca ...

starting in the

Cretaceous The Cretaceous ( ) is a geological period that lasted from about 145 to 66 million years ago (Mya). It is the third and final period of the Mesozoic Era, as well as the longest. At around 79 million years, it is the longest geological period of ...

until the

Tertiary Tertiary ( ) is a widely used but obsolete term for the geologic period from 66 million to 2.6 million years ago. The period began with the demise of the non-avian dinosaurs in the Cretaceous–Paleogene extinction event, at the start ...

with the Arzacq syncline to the north and the

Eocene The Eocene ( ) Epoch is a geological epoch that lasted from about 56 to 33.9 million years ago (mya). It is the second epoch of the Paleogene Period in the modern Cenozoic Era. The name ''Eocene'' comes from the Ancient Greek (''ēṓs'', " ...

flysch Flysch () is a sequence of sedimentary rock layers that progress from deep-water and turbidity flow deposits to shallow-water shales and sandstones. It is deposited when a deep basin forms rapidly on the continental side of a mountain building epi ...

trough in front of the

Pyrenees The Pyrenees (; es, Pirineos ; french: Pyrénées ; ca, Pirineu ; eu, Pirinioak ; oc, Pirenèus ; an, Pirineus) is a mountain range straddling the border of France and Spain. It extends nearly from its union with the Cantabrian Mountains to ...

foothills Foothills or piedmont are geographically defined as gradual increases in elevation at the base of a mountain range, higher hill range or an upland area. They are a transition zone between plains and low relief hills and the adjacent topogr ...

to the south. The field is 16 km long and 10 km wide with oil produced beneath a Tertiary

unconformity An unconformity is a buried erosional or non-depositional surface separating two rock masses or strata of different ages, indicating that sediment deposition was not continuous. In general, the older layer was exposed to erosion for an interval ...

at 700 m and gas, with high hydrogen sulfide content, beneath a pre-

unconformity at about 4000 m. The anticline was identified with two

exploration geophysics Exploration geophysics is an applied branch of geophysics and economic geology, which uses physical methods, such as seismic, gravitational, magnetic, electrical and electromagnetic at the surface of the Earth to measure the physical properties of ...

electric lines in 1943 and a

magnetotelluric Magnetotellurics (MT) is an electromagnetic geophysical method for inferring the earth's subsurface electrical conductivity from measurements of natural geomagnetic and geoelectric field variation at the Earth's surface. Investigation depth ra ...

survey in 1943, a gravimetric survey in 1944 and a reflection seismology survey in 1947, which led to the Lacq No. 1 well in 1949. The

stratigraphic column A stratigraphic column is a representation used in geology and its subfield of stratigraphy to describe the vertical location of rock units in a particular area. A typical stratigraphic column shows a sequence of sedimentary rocks, with the oldest ...

begins with the

Lower Jurassic The Early Jurassic Epoch (in chronostratigraphy corresponding to the Lower Jurassic Series) is the earliest of three epochs of the Jurassic Period. The Early Jurassic starts immediately after the Triassic-Jurassic extinction event, 201.3 Ma&nb ...

Liassic at about 4700 m followed by the

Late Jurassic The Late Jurassic is the third epoch of the Jurassic Period, and it spans the geologic time from 163.5 ± 1.0 to 145.0 ± 0.8 million years ago (Ma), which is preserved in Upper Jurassic strata.Owen 1987. In European lithostratigraphy, the name ...

Dogger, the gas producing dolomite in the Portland Group, Purbeckian-Waeldian

sandstone Sandstone is a clastic sedimentary rock composed mainly of sand-sized (0.0625 to 2 mm) silicate grains. Sandstones comprise about 20–25% of all sedimentary rocks. Most sandstone is composed of quartz or feldspar (both silicates ...

, and

Valanginian In the geologic timescale, the Valanginian is an age or stage of the Early or Lower Cretaceous. It spans between 139.8 ± 3.0 Ma and 132.9 ± 2.0 Ma (million years ago). The Valanginian Stage succeeds the Berriasian Stage of the Lower Cretace ...

Neocomian In geology, Neocomian was a name given to the lowest stage of the Cretaceous system. It is generally considered to encompass the interval now covered by the Berriasian, Valanginian and Hauterivian, from approximately 145 to 130 Ma. It was introdu ...

limestone Limestone ( calcium carbonate ) is a type of carbonate sedimentary rock which is the main source of the material lime. It is composed mostly of the minerals calcite and aragonite, which are different crystal forms of . Limestone forms whe ...

and dolomite, followed by the

Albian The Albian is both an age of the geologic timescale and a stage in the stratigraphic column. It is the youngest or uppermost subdivision of the Early/Lower Cretaceous Epoch/ Series. Its approximate time range is 113.0 ± 1.0 Ma to 100.5 ± 0 ...

- Aptian

marls Marl is an earthy material rich in carbonate minerals, clays, and silt. When hardened into rock, this becomes marlstone. It is formed in marine or freshwater environments, often through the activities of algae. Marl makes up the lower part o ...

and limestones.Winnock, E., and Pontalier, Y., 1970, Lacq Gas Field, France, AAPG Memoir 14: Geology of Giant Petroleum Fields, Tulsa: AAPG, pp. 375-378.

References

{{DEFAULTSORT:Lacq Gas Field Natural gas fields of France