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7 3,759,328 horizontally separated patterns that each contain one or more wells opening into a layer rich in water soluble minerals can be operand as described in connection with FIG. 2 to form horizontally expanding permeable zones and produce shale oil. The sizes of the permeable zones can be monitored by means oC acoustic, clecvo- magnetic the like meazuremenu of the ezunu of the substantially void space and/or measuremcnu of the volume of fluids that are contained into caverru. The horizontal expansion of the caverns can be controlled to provide an efficient recovery of oil from noninter- secting, generally vertically extensive zones that are spaced so that undisturbed columns capable of sup- porting the overburden are lefr between the depleted zones. During the initial stages of expanding a tvbble- containing cavern in accordance with the prcunt pro- cess, it is not necessary and is generally undesirable to use a temperature high enough to decompox a pre- dominant proportion of the fluid•contacud heat unsi- tive carbonate material, It is preferable to keep the cav- ern substan[iallyfull o(aqueous liquid in which the car• bonate material is soluble. This unds to provide the best heat economy since it minimizes the decomposi- tion reaction (which is an endothermic reaction that comsumes heat). In order to keep the cavern substan- tially filled with aqueous liquid it is preferable to main- tain the pressure within the cavern above the decompo- sition pressure of the heat xnsitive carbonate material at the [emperature within the cavern. [n general the pressure within the cavern cannot be kept high enough to prevent such a decomposition during an oil recover- ing stage. The retorting and hydrocarbon recovery is preferably conducted at a temperature above about 500° F, and at the depths at which oil shalt is usually encountered, the pressure in the cavern cannot be high enough to prevent decomposition of heat xnsitive car• bonate material at such a temperature, without a dan- ger of ereatinglarge xalefractures which are extended into locations in which (ractures are undesirable. When one or a plurality of generally vertcaly exten• attic permeable zones have been expanded horizontally to substantially the extent desired, the circulation of fluid within throne zones or caverns is preferably ad- justed to minimize the rate of horizontal growth and/or maximize the rate of oil recovery. Such an adjustment can be effected by increasing the temperature and/or decreasing the aqueous liquid content of the fluid within the cavern. A higher temperature tends to in• crease the rate of oil recovery (particularly with re• specs to the gaseous componenu of shale oil). Altcma- tivcly, adecrease in the aqueous liquid conunt tends to reduce the rate of dissolution o! soluble mineral. Whcrc the removal of solid material hom the oil shale ie confined to a removal of the fluid products of the py- rolyeie reaction and/or the COs and water vapor pro- i duced by the decomposition of heat unsitive Carbon-' arcs, the volume of the depleted oil shale tends to be eutlicient, relative to the volume o(solids that are re• moved, to terminate the growth o(the permeable zone (unless the oil shale is ono that contains an exception- ally large propo~on of heat sensitive carbonate min• eral).The aqueous liquid content of the fluid within [he cavern can be reduced by, for example, circulating sub- stantially dry steam, or a mixture oC a dry steam and e.g., carbon dioxide, et a race end temperature at which aqueous liquid lift within the cavern Contains a rela- tively high proportion oC inert inorganic solute. F1G. 3 shoos downhole equipment of the type shown in FIG. 1 arranged to effect a dowmhole separation of S the gaxous and liquid phaxs oC the fluid being pro- duced. Particularly when the concert[ration of heat sen- sitive carbonate material is relatively high, and/or the temperature of the inflowing hot aqueous fluid is rela- tively high, a significant amount of gaxous carbon di• IO oxide and water will be formed. However, to the extent that it is [easible, it is desirable to produce a relatively cool liquid phase fluid that contains a sign Jcant pro• portion of produced shale oil hydrocarbon. !n the ar- rangement shown in FIG. 3, borehole 20 is equipped t5 with pipe strings 21, 22 and 23. Some or all o[ such pipes are preferably thermally insulated, as indicated by coatings 24 on pipes 21 and 22. Pipe 21, through which the hot aqueous fluid is inflowed, opens into [he borehole at a relatively shallow depth. Pipe 22 extends 20 to an intermediate depth and is used to outlow fluid that is relatively cool but is predominately- gaseous. Pipe 23 extends to a relatively deep depth, is preferably equipped wi[h doumhole pumping means (not shown), and is uxd to ouNou• fluid that is predominately liquid. 23 The vertical xction of borehole between the ends of pipes 22 and 23 xrves as a downhole gravity of xpara- tion chamber. Steam or a mixture of steam and hot aqueous liquid (hot water) is inflowed through pipe 21. The inflowing 30 honest and lightest gas lends to remain above the Goole[ and heavier gas and in situ generated carbon di- oxide. The cooler gases outflow through pipe 22 while the honer and lighter inflowing gaxs tend to t:ow along the walls oC the cavern. Where desirable a relatively 35 light and cool gas, such as methane, hydrogen, elc., can be maintained substantially static, or slowly- injected, through and around the upper portion of the borehole and cavern. Once the rubbled oil shale cavern has been estab- a0 lished and the heat xnsitive minerals and water-soluble carbonates removed as an aqueous solution, the hydro- carboru (oil) can be recovered by suitable means such as by contacting the cobbled oil shale within the cavern with a pyrolyzing fluid to effect decomposition of the a3 kerogens to hydrocarbon which is removed from the formation. In recovering the hydrocarbons, the pyro• 1}-zing fluid can be injected (FIG. 1) via 7 and recov- ered via tubing 8 visa versa and in a dual sytem az shoum in FIG. 3 the pyrolyzing fluid such as steam can SO be injec[cd via tubing string 2] and the hydrocarbons recovered via 22 or the process can be reverxd. I[ is understood that various changes in the detailed dcxribed to explain the invention can be made by per- i5 'SOns skilled in the art within the xope of the invention as ezpresxd in the appended claims. 1 claim as my invention: 1. In a process for expanding a zone of permeability within a subterrurean oil shale by forming a permeable zone within a portion that contairu heat xnsitive car- bonate mineral and circulating hot aqueous fluid within the permeable zone, the improvement which eom- prixs: inllowing hot aqueous fluid in[o contact with a sub• ~S terranean portion of oil shale that contains heat unsitive carbonate mineral at a relatively shallow depth, the umperature otsaid inflowing Ouid being