NOVELTY - Process for in situ production of methane gas comprises: selecting one or more layers rich in natural kerogens, preferably kerogens having ratio of H:C of greater than or equal to 1, in the superficial geological subsoil of up to 1500 m of depth, preferably up to 500 m; stimulating the growth and activity of indigenous microorganisms naturally and locally contained in the natural kerogens to increase the degradation of kerogens and the methane production in the kerogens; and extracting the produced methane, gradually from its production.    USE - The process is useful for in situ production of methane gas.    ADVANTAGE - The process: provides methane gas with high yield; and is rapid, inexpensive, simple and easy to implement.    DETAILED DESCRIPTION - INDEPENDENT CLAIMS are included for:    (1) a fluids to be injected to increase the methane production in one or more layers of kerogens, comprising: water; nutrients for methanogenic and syntrophic microorganisms; at least one adjuvant, preferably at a concentration of 10-9 to 5 g/l of fluids; optionally carbon dioxide, preferably obtained by a recycling; and optionally hydrogen;    (2) a composition of nutrients partly constituting the fluids comprising trace elements, complete vitamin solution, organic trace elements, inhibitors of indigenous microbial populations competing with the indigenous methanogenic microbial populations, preferably inhibitors of heterotrophic bacteria, preferably denitrifying bacteria and native sulfate-reducing bacterial, a nitrogen source, preferably ammonium chloride, a source of phosphate, preferably dipotassium phosphate, a source of acetate ions, preferably sodium acetate, sodium acetate, a source of hydrogen carbonate ions, preferably sodium bicarbonate, and a source of peptides, preferably of trypticase (also known as tryptone or casein peptone);    (3) a composition of trace elements forming part of the composition of nutrients comprising at least: boron, preferably in the borate form (BO3-3); vanadium in its vanadate form (VC4-2), copper, preferably in its chloride form, iron, preferably in its chloride form, magnesium, preferably in its chloride form, zinc, preferably in its chloride form, nickel, preferably in its chloride form, cobalt, preferably in its chloride form, lithium, preferably in its chloride form, potassium, preferably in its chloride form, manganese, preferably in its chloride form, Optionally sodium, preferably in their chloride form, aluminum in its aluminopotassium form (AlK (OH)2), calcium, preferably in its chloride form, and optionally selenium, in its sodium selenite form (Na2SeO3);    (4) a composition of a complete vitamin solution partly constituting the composition of nutrients comprising at least: thioctic acid (or alpha lipoic acid), biotin, folic acid, pyridoxine and/or pyridoxine chlorohydrate, thiamine with or without hydrochloric acid, riboflavin, nicotinic acid, calcium pantothenate, p-aminobenzoic acid, cobalamin, and optionally ascorbic acid;    (5) a composition of inhibitors of indigenous microbiological populations competing with indigenous methanogenic microbial populations, partly constituting the fluids comprising nitrites, sulfites, molybdate, and/or ferric oxides; and    (6) a device for methane production comprising at least: means for injecting fluid, preferably by hydraulic pumps, in one or many layers rich in natural kerogens through which fluids percolate; means of metabolic forcing of indigenous microorganisms by the fluids injected by the injection means; means for pumping fluids that percolated through the kerogens and containing produced methane; means for collecting the produced methane, e.g. means for separating; means for compressing collected methane; and means for storing and/or distributing collected and compressed methane.