Impermeation of Porous Media by Forming Hydrates In Situ

Abstract

Given favorable reservoir conditions, the method suggested here of plugging porous media by convection-conduction cooling and agitation of the water porous media by convection-conduction cooling and agitation of the water saturating the medium so as to "grow" a gas-hydrate barrier can be useful in creating underground gas storage facilities. Introduction Certain gases - such as CO2, H2S, SO2, and natural gas and manufactured gas consisting chiefly of light paraffinic hydrocarbons - form solid gas hydrates paraffinic hydrocarbons - form solid gas hydrates when they contact water in sufficient amounts, within a range of pressure and temperature. Gas hydrates may be developed under pressure of a few hundred psi and at temperatures substantially above the psi and at temperatures substantially above the freezing point of water. Gas hydrates cause much trouble in the gas industry by "freezing" (plugging) the gas well tubing, the flow lines within the surface treatment and measurement facilities, and the gathering pipes. They may be useful, however, in the local impermeation* of porous and permeable media. The proposed method, detailed under the section on applications, involves localized convection-conduction cooling of the water saturating the porous medium to grow gas hydrates in the pore spaces and pore channels as the water comes in contact with a gas capable of forming hydrates. At the outset it was assumed that gas hydrates may be initiated and propagated through partially water-saturated porous propagated through partially water-saturated porous rock, a presumption that is heretofore unsupported by available experimental evidence. The purposes of the laboratory experiments reported here were to establish ifgas hydrates may be formed in porous rock, andformation of gas hydrates reduces (or eliminates) rock permeability. Localized elimination of permeability by this means may be used to stop leaks in caprocks or otherwise to bar the migration of gas, as from under a spill point of anticlinal storage reservoirs, or to close partially the outcropping end of a porous bed of a homocline to develop storage conditions. Laboratory Investigations Experimental Apparatus The experiments were designed to incorporate Geo-Engineering Laboratories' high-pressure test cell with confining pressures on core samples up to 7,500 psig. Cooling coils around the cell, connected to a refrigeration unit, provide a controlled temperature range down to 28 degrees F (Fig. 1). Fig. 2 is a flow diagram of the test apparatus. A core sample 3 1/2 in. in diameter and 7 in. long is encased within the HP cell and provided with appropriate input (base) and output (top) provided with appropriate input (base) and output (top) tubing connections and thermocouple leads extending through the base of the cell. The gas flow circuit runs from the high-pressure gas source, through the flowmeter manifold (which provides for alternative upstream or downstream flow provides for alternative upstream or downstream flow sensing), through the water column saturator and water trap, to the pressure gauge and the high-pressure side of the differential pressure gauge, then into the lower end of the core. From the upper end of the core the gas flows to the low-pressure side of the differential pressure gauge, to the variable orifice (valve), to the gas dryer and back through the flow-meter manifold. JPT P. 1059