|
<br />3
<br />
<br />3,759,328
<br />portion o[ oil shale chat contains heat sensieive carbon-
<br />ate mineral and is underlain by a portion or layer that
<br />contains water soluble mineral. The water soluble min-
<br />eral is solution mined or leached for example, by means
<br />of a process of the type described in copending patent
<br />application Ser. No. 770,964; filed Oct. 28, 1968, now
<br />abandoned, and Ser. No. 860,349; filed Sept. 23, 1969,
<br />now abandoned. Those applications describe proce•
<br />dares (or utilizing a water soluble mineral-rich portion
<br />of an oil shale to form a cavem that can be expanded
<br />before or during the recovery of shale oil from the oil
<br />shale exposed in and around the cavern. Such a rota-
<br />tion mined cavem in or adjacent to an oil shale that
<br />contains heat sensitive carbonate mineral can advanta-
<br />geously be utilized as a horizontally extensive cavern
<br />that is expanded vertically during the horizontal expan-
<br />sion of a venieally extensive cavernous zone, such az a
<br />section of a borehole.
<br />Referring to the drawing, FIG. 1 shows a portion of
<br />a well borehole 1 which has been drilled through an
<br />overburden 2, comprising successively shallower earth
<br />formations, and opened into an oil shale formation 3
<br />that contains a heat sensitive carbonate mineral. The
<br />oil shale formation that is placed in fluid communica-
<br />tion with a portion of the borehole to be uxd N prac-
<br />ticing the present invention, should be a (ormation con-
<br />taining asignificant proportion, e.g., grea[er than 5 per-
<br />cent by weight, of heat sensitive carbonate mineral.
<br />Borehole 1 is equipped with a string of Gazing 4, which
<br />is bonded to the surrounding earth formations by ce-
<br />ment 5.
<br />Separate conduiu for conveying Raids between a sur-
<br />face location and, respectively, relatively shallow and
<br />relatively deep depths within the oil shale are provided
<br />by tubing strings 7 and 8. Alternatively, such conduits
<br />may comprise two or more parallel swings of tubing
<br />and may be located in two or more well boreholes that
<br />intersect or extend into a common cavern within the
<br />oilshale. Such conduits can be installed and equipped
<br />by means of known procedures and devices and heat
<br />insulation (not shown) is preferably installed around at
<br />least those of such conduits that are uxd for the intlow-
<br />ing of hot fluid.
<br />As indicated by FIG. 1, the vertically extensive cav-
<br />ern or opening that is expanded by the prexnt process
<br />can comprise the borehole of a well that extends into
<br />an interval of oil shale that contains heat xnsitive car-
<br />bonate material. Such an interval preferably has a verti-
<br />cal thickness of at least about ]00 feet. In the initial
<br />stages, such a boreholemay have a generally cylindri-
<br />cal form, such as indicated by the dotted line la, and
<br />may comprise a relatively slender, generally vertical
<br />cavern within the oil shalt. In operating the process
<br />with the equipment shown in FIG. 1, a hot aqueous
<br />fluid is (lowed into contact with the wall of the cavern
<br />by inflowing hot aqueous gas and/or liquid through the
<br />annulus within pipe 8 (i.e., the space between pipes 7
<br />and 8) and through adjacent perforations 6 at a rela-
<br />tively shallow depth within the carbonate mincral-
<br />containing portion of the oil shale. The inflowing fluid
<br />such as hot water and/or steam flows downward along
<br />the face of the vertical interval of oil shale (along the
<br />wall of the borehole) and dccompoxs and dissolves the
<br />heat sensitive carbonate mineral material. The dissoly
<br />ing of water soluble material forms a liquid solution 9.
<br />4
<br />is out-flowed through pipe 7, which extends to a rela-
<br />tively low level within the borehole. The decomposing
<br />and dissolving of carbonate mineral components of the
<br />oil shale cauxs the spalling and caving in o[ particles
<br />5 10 of the oil shale and cauxs a generally horizontal ex•
<br />pansion of arubble-containing cavernous tone of per-
<br />meabiliry within the oil shale.
<br />Where the oil shale being treated contains a signifi-
<br />cant proportion of a mineral, such az a halite, which is
<br />10 water soluble in iu natural form, the inflowing of hot
<br />aqueous fluid can advantageously be preceded by a cir-
<br />culation of aqueous liquid at a relatively low tempera-
<br />ture, such as the wellhead temperature, the tempera-
<br />ture of the source olthe liquid or the like. In such apre-
<br />t3 treatment, the cvculating liquid may leach out signifi-
<br />cant portions of distributed layers or particles of the
<br />soluble mineral. This increases the surface area of ex-
<br />posed oil shale and/or weakens the support for layers
<br />or chunks of the oil shale. such a pretrcatmcnt circula-
<br />=0 tion can advantageously be continued while the rate of
<br />dissolution is high, e.g., az indicated by the proportion
<br />of solute in the outllowing liquid. The so-circulated
<br />aqueous liquid can then be gradually or rapidly heated
<br />to the temperature xlected for the inflowing hot aque-
<br />23 our liquid uxd to decompose heat xnsitive carbonate
<br />material, with or without an interruption oC the flow
<br />through the cavern.
<br />When necessary or desirable the vertical expansion
<br />of the cavem can be inhibited by spotting and main-
<br />30 taining a relatively light and cool fluid 13 along the roof
<br />of the cavern. Such a fluid is preferably a gaz and can
<br />in inflowed, or maintained substantially stationary, in
<br />and around the annulus within Gazing 4 (i.e., the space
<br />between pipe 8 and casing 4) and the upper portion of
<br />35 borehole I (below cement 5) to extend along the roof
<br />of the horizontally expanding cavem az the walls oC the
<br />cavern more radially outward to and beyond the Loea-
<br />tion shown a[ ]b.
<br />The hot aqueous fluid uxd in the presen[ cavern-
<br />40 enlarging procedure is preferably steam, hot aqueous
<br />liquid (hot water) or a mixture of such fluids. The hot
<br />fluid is preferably inflowed a[ a temperature, e.g., at
<br />least about 250' F, that is significantly higher than the
<br />normal temperature of the subterranean oil shale for-
<br />45 motion. The heat transported by such a hot fluid con-
<br />verts the heat xnsitive carbonate material to carbon
<br />dioxide and water vapor within portions of the nor-
<br />mallyunpertneable oil shale matrix. Such a generation
<br />50 of gas causes localized frac[uring and/or spalling of the
<br />oil shale.
<br />The aqueous liquid component of the inflowing hot
<br />paid dissolves water salable mineral material and cre-
<br />ates additional solid•free void space. This occurs along
<br />SS most, if not all, of the vertical extent oC the flow path
<br />uxd in the prexnt process. The spalling and dissolu-
<br />tion causes a horizontal expansion of a rvbble-
<br />containingcavem. The inflowing hot aqueous (laid can
<br />comprix super heated, dry, or wet steam, or a mixture
<br />~ o(such a steam with substantially any gas vapor or liq•
<br />aid, such az carbon dioxide, phenols, hydrocarbons, al-
<br />cohols, halogenated hydrocarbons, acids, or (hc like, or
<br />with substantially any aqueous solution, such as an
<br />aqueous acid or box or solution or neuval salt. Where
<br />63 ~0 mflou•ing (laid is substantially completely gaseous
<br />tt should contain sufficient steam to provide a signifi-
<br />i
<br />1 ~F
<br />\°t`~
<br />
|