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 prese ...

located in

Nouvelle-Aquitaine Nouvelle-Aquitaine () is the largest Regions of France, administrative region in France by area, spanning the west and southwest of Metropolitan France. The region was created in 2014 by the merging of Aquitaine, Limousin, and Poitou-Charentes ...

. Discovered in 1950, it was developed by

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

, determining it to have initial total

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

of the Lacq gas field are around 8.8 trillion ft³ (251 km³). It began production of

natural gas Natural gas (also fossil gas, methane gas, and gas) is a naturally occurring compound of gaseous hydrocarbons, primarily methane (95%), small amounts of higher alkanes, and traces of carbon dioxide and nitrogen, hydrogen sulfide and helium ...

and condensates in 1958, with a production rate of around 1 billion ft³/day (35×10⁵ m³).

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 Hydrocarbon, hydrocarbons in a petroleum reservoir, reservoir. Traps can be of two types: stratigra ...

located in an

anticline In structural geology, an anticline is a type of Fold (geology), fold that is an arch-like shape and has its oldest Bed (geology), beds at its core, whereas a syncline is the inverse of an anticline. A typical anticline is convex curve, c ...

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 143.1 to 66 mya (unit), million years ago (Mya). It is the third and final period of the Mesozoic Era (geology), Era, as well as the longest. At around 77.1 million years, it is the ...

until the

Tertiary Tertiary (from Latin, meaning 'third' or 'of the third degree/order..') may refer to: * Tertiary period, an obsolete geologic period spanning from 66 to 2.6 million years ago * Tertiary (chemistry), a term describing bonding patterns in organic ch ...

with the Arzacq

syncline In structural geology, a syncline is a fold with younger layers closer to the center of the structure, whereas an anticline is the inverse of a syncline. A synclinorium (plural synclinoriums or synclinoria) is a large syncline with superimposed ...

to the north and the

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

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 ep ...

trough in front of the

Pyrenees The Pyrenees are a mountain range straddling the border of France and Spain. They extend nearly from their union with the Cantabrian Mountains to Cap de Creus on the Mediterranean coast, reaching a maximum elevation of at the peak of Aneto. ...

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

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 a hydrosulfuric gas 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 at the surface of the Earth, such as seismic, gravitational, magnetic, electrical and electromagnetic, to measure the physical properties o ...

electric lines in 1943 and a magnetotelluric survey in 1943, a gravimetric survey in 1944 and a

reflection seismology Reflection seismology (or seismic reflection) is a method of exploration geophysics that uses the principles of seismology to estimate the properties of the Earth's subsurface from reflection (physics), reflected seismic waves. The method requir ...

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 Liassic at about 4700 m followed by the

Late Jurassic The Late Jurassic is the third Epoch (geology), epoch of the Jurassic Period, and it spans the geologic time scale, geologic time from 161.5 ± 1.0 to 143.1 ± 0.8 million years ago (Ma), which is preserved in Upper Jurassic stratum, strata.Owen ...

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

sandstone Sandstone is a Clastic rock#Sedimentary clastic rocks, clastic sedimentary rock composed mainly of grain size, sand-sized (0.0625 to 2 mm) silicate mineral, silicate grains, Cementation (geology), cemented together by another mineral. Sand ...

, and

Valanginian In the geologic timescale, the Valanginian is an age or stage of the Early or Lower Cretaceous. It spans between 137.05 ± 0.2 Ma and 132.6 ± 0.2 Ma (million years ago). The Valanginian Stage succeeds the Berriasian Stage of the Lower Cretac ...

- Neocomian

limestone Limestone is a type of carbonate rock, carbonate sedimentary rock which is the main source of the material Lime (material), lime. It is composed mostly of the minerals calcite and aragonite, which are different Polymorphism (materials science) ...

and dolomite, followed by the

Albian The Albian is both an age (geology), age of the geologic timescale and a stage (stratigraphy), stage in the stratigraphic column. It is the youngest or uppermost subdivision of the Early Cretaceous, Early/Lower Cretaceous epoch (geology), Epoch/s ...

Aptian The Aptian is an age (geology), age in the geologic timescale or a stage (stratigraphy), stage in the stratigraphic column. It is a subdivision of the Early Cretaceous, Early or Lower Cretaceous epoch (geology), Epoch or series (stratigraphy), S ...

marls 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