US 2988143 A
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C. B. SCOTTY June 13, 1961 PROMOTING FLOW IN SUBSURFACE PRODUCING FORMATIONS Filed Sept. 22, 195] JNVENTOR. LW
- A'TTOENE'x/g' United States Patent lO Filed Sept. 22, 1951, Ser. No. 247,795 9 Claims. (Cl. 166-36) The present invention relates to the opening up of subsurface formations to increase the production of liquids therefrom and particularly to the production of extensive radial formation fracturing about a well bore for improving iluid ow between the formation and the well bore.
The invention is therefore particularly applicable to producing petroleum wells in which physical disintegration of the producing structure substantially promotes hydrocarbon flow into the well bore.
The present invention especially contemplates the Selective localization of fracturing at a predetermined point in the well bore by initiating fracture of the formation with a directional explosive shot and extending the disrupted area by hydraulic fracturing under fluid pressure substantially greater than the formation pressure. More specifically, a substantial fracture or fissure is localized at desired elevation within the producing formation by a directional jet blast of a shaped charge, high explosive. The initial penetration or localized fissure may be carried by means of a projectile from a perforating gun. It is preferred, however, to effect the initial blasting of the formation bythe directional jet blast of a shaped charge utilizing the Munroe effect. By this means an explosive blast directed radially toward the bore hole will extensively disintegrate a typical consolidated producing formation, and produce fissures and fractures extending radially outwardly in the direction of `the shot. Thereafter, a hydraulic squeeze, applied under formation fracturing pressures disrupts the formation along an extension of the fissures formed by the explosive fracture, and thus radially extends the fracture at the selected elevation in the well bore.
The explosive shooting of the formations, which has hitherto been extensively used, forms, per se, no part of the present invention. Therefore, no detailed description is necessary. In general, however, the shooting is effected by a charge of high explosive material provided with a wedge-shaped recess or concavity in its directional face proportioned to focus the explosion in a straight line axially and outwardly of the recess. The thus focused explosion, as is known, possesses a greatly increased penetrating capacity.
The charge may comprise a cylinder in which the directional effect is produced by a coaxially arranged conical recess in one extremity. Therefore, such a charge is preferably exploded within the well bore from a horizontal position such that its axis extends radially of the well bore, with the recessed or directional end of the cylinder facing the formation. In order to produce a fracture extending circumferentially about the well bore, a plurality of such charges may be annularly disposed at the desired level with their directionally effective ends facing the formation.
Alternatively, to realize a similar effect, a single, annular or cylindrically shaped charge, having a directionally shaped outer cylindrical face may be disposed coaxially of the well bore and exploded in this position. This type of shaped charge is typified by that employed in the art for cutting pipe casings in underground formations, in which the explosive charge takes the form of an annular ring, disc, or cylinder, and having a continuous, V-shaped groove in its outer face and extending annularly about its central axis.
It is not essential, however, to the present invention that the explosive disruption take place on all sides of the Well bore since substantial explosive fracturing or aperturing of the formation at the desired level serves to initiate the desired extension of the fracture in all directions parallel to the bedding plane upon application of sufficient hydrostatic squeeze pressure. This apparently follows from the fact that iissuring or fracturing, initiated by jet explosion, is more readily extended than is the initiation of new fractures or existing discontinuities at other elevations in the well bore.
The hydraulic or squeeze fracturing of earth formations as is known, per se, is ordinarily elected with jellied gasoline or similar hydrocarbon of suicient viscosity to resist dissipation in the porous, producing formation. Therefore, as the liquid is injected into the well, the hydrostatic pressure placed upon the formation progressively increases. With a suflcient velocity and pressure of injection at the well head, the consolidating pressure on the formation is overcome and the lateral fracturing is extended as desired. After the desired disruption of the subterranean area has been accomplished, the formation is usually treated to decrease the viscosity of the injected liquid so that formation uids can ow into the well bore.
For example, an effective fracturing fluid may comprise a naphtha fraction or a crude oil containing a substantial proportion of Napalm, which is the soap constituent of the known jellied gasoline. After the fracturing is completed, the Napalm jell tends, inherently, to revert to the original viscosity of the hydrocarbon, and this reversion is expedited by the presence of small amounts of water. Therefore, the subterranean or connate water ordinarily encountered is usually effective. However, to expedite the effect, the fracturing treatment may be followed by formation injection of a jell-breaker solution, as for example, a 2% solution of petroleum sulfonate in gasoline or crude oil.
Thereafter, in the case of a producing petroleum well, production is resumed and the treatment materials are flushed out of the formation by the produced crude.
It is to be understood that the present invention is not limited to these specific details of hydraulic fracturing given only by way of illustrating the type of operation contemplated. In general, the present invention contemplates employing the current or usual techniques of hydraulic fracture, which, per se, form no part thereof.
The present invention is of particular advantage from the standpoint of controlling the location of hydraulic fracture at the desired region of the producing formation. This is of great importance as regards the selective opening up of channels in the producing formation rather than along the boundaries of such area or even externally thereof within adjacent non-producing, poorly compacted strata. The underground formations, as is known, are characteristically stratified, and any nearby, poorly compacted strata will ordinarily tend to fracture in preference to the producing formation. Likewise, in shale formations, the point of fracture is generally at the shale boundary so that optimum drainage of the subsurface fluid into the fractures is not realized. In short,in a typical underground structure, the hydraulic fracturing tendency is maximized along formation planes which are only infrequently planes of optimum hydrocarbon production. Therefore, the present invention is particularly beneficial from the standpoint of controlling the zone of hydraulic fracturing for effecting the maximum ow into the well bore.
The invention, moreover, particularly contemplates the simultaneous application of localized explosive disruption of the formation with hydraulic fracturing in order to combinethe essentially simultaneous disruptive effect of these two media of fracture. More specifically, it is con templated detonating lthe directional charge or charges at or Vabout critical hydraulic fracturing pressure. Under this combined effect, fracturingis particularlyextensive, the shock of the explosion not only serving to initiate hydraulic fracturing, but to materially extend the effect thereof far greater than is characteristic of hydraulic fracturing alone, and, thus extending Ythe utility and productivity far beyond anything hitherto contemplated.
This is to be particularly contrasted with the procedure proposed in the U.S. Patent No. 2,547,778, to precede the hydraulic fracture by under-reaming the formation at the desired point of fracture. Entirely apart from the cost and difficulties of localized under-reaming, such treatment lacks the improved initiating effect of the fracturing and the striation which is caused by the jet blasting. Moreover, excessive under-reaming is usually necessary to produce a discontinuity of greater magnitude than naturally. occurring discontinuities along the well bore, and thus to localize the fracture as desired rather than at some spaced point of discontinuity, as for example, in an adjacent, poorly consolidated sand or shale.
In direct contrast, the present invention is highly effective in localizing and improving the extent of fracture, as previously indicated.
One embodiment in the present invention is illustrated more or less diagrammatically in the accompanying drawing wherein FIGS. 1-3 represent a vertical section through the lower end of a producing well at successive stages of treatment. ln these figures 10 represents a bore hole extending into a producing formation 11. A casing 12 terminates above the producing formation and is cemented in place as at i3.
A cable i lowered from the surface suspends, als indicated, an explosive jet perforating gun comprising a sinker bar 16 to the lower end of which is affixed, by means not shown, a jet directional explosive charge 17. The shaped charge i7 comprises a high explosive disc within a plastic housing f8. it is to be noted that the disc or cylindrically shaped mass of explosive possesses a shaped annular periphery having the characteristic V recess or indentation extending radially 4into its outer face and progressing annularly and continuously thereabout. Preferably the face of the v' recess, indentation or groove 19 is enclosed by Va V shaped retainer 20 which may be formed. of plastic or some convenient sheet metal such as aluminum.
As indicated, the charge is suspended coaxially of the bore hole with the annular groove facing in a direction parallel to the bedding plane of the formation. The explosion is thus focused to greatly multiply the disruptive effect radially out into the formation.
In a preferred practice of the present invention, the upper or surface extremity of the well casing is continuously injected with fracturing liquid 22 under pressure and at a substantial rate to fill the well bore and progressively increase the pressure thereof to the formation fracturing range.
As above intimated, it is contemplated observing an iujection rate in excess of the rate of liquid ow into the formation, if any, and thus sufficient to realize the fracturing pressures. ln accordance with this embodiment, the pressure on the squeeze liquid 22 is rst raised to the range of incipient fracture for detonation of the explosive charge.
FIGURE 2 is intended to exemplify the transient condition produced by the initial penetrating effect of the explosion, at this time driving recesses selectively into the formation locally about the well bore opposite the directional faces of the explosive and opening up substantial lateral fissures and fractures 24.
FIGURE 3 illustrates the subsequent extension of the initial fractures far into the formation by thelifting effect of the hydrostatic head. Manifestly, the initially formed recesses and fractures expose wide areas of lateral l surfaceagainst which the lifting effect of the hydraulic fluid reaches maximum effectiveness. The extent and ease of fracture are therefore materially improved. Moreover, the extensive radial opening up of the porous formation radially increases the surface area of producing vformation surface in free flowing relation to the well bore. Therefore, in the case of poorly permeable formations, the contained fluid flows toward the producing Well at a materially increased rate of production. Thus, the invention contemplates extensive and improvedflocalized fracturing or disruption of the formation at predetermined elevations parallel to the bedding plane to increase the radial zone from which oil may flow freely.
While, as above indicated, essentially simultaneousaction of the explosive and hydrostatic disruptive forces is preferred, nevertheless the invention may be advantageously practiced lby carrying out the formation shooting substantially in advance of hydrostatic fracturing. This follows from the fact that the shock of the explosion in addition to piercing and aperturing the `formation `for a substantial distance produces far more extensive radial striations or incipient fissuring which thereafter are readily opened by a hydraulic squeeze. It is believed on a theoretical basis that the lateral, explosively produced striations `form extensive avenues of uid migration along which the hydrostatic liuid preferentially migrates to maximize `the upward thrust which is essential to lifting the overburden and effecting the hydrostatic fracture, and that this effect is not impaired even though the migration involves only thin sections of liquid.
It is to Ibe understood that the liquid used for fractguring may be mixed with sand or gravel to sustain and support the channels of fiow after fracturing occurs. So also Vit iscontemplated treating the bore hole, previous to hydraulic pressuring, to form a relatively impermeable filter cake on the exposed formation surfaces. As is apparent from the foregoing, the filter cakeI restrains loss of fracturing liquid to the formation, but does not impair its movement into the explosively formed fractures `toV exert maximum vertical lifting effect at this region.
The hydraulic step may advantageously be performed with the aid of open hole p-ackers, and where the fracturing liquid is pumped into the well through tubing, `the tubing may be secured to the casing by means of a packer. It is similarly contemplated resorting to the other known techniques `of liquid formation fractuiing per se. Moreover, as above intimated, for the a-nnularly effective explosive `charge illustrated in the foregoing embodiment, there may be substituted one or more cylindrical charges ydirectionally effective at one axial extremity, since substantial initiation of `fractureat one or more ,points in the kperiphery of the bore hole is almost as effective `as completeannularfracture as regards initiating thefinal desired fluid pressure disruption. y
After the desiredV enlargement of the fractures the formation may be swabbed or flushed as aboveV indicated and production resumed at a substantial increased rate.
Obviously, many modifications and variations of the invention as Vhereinbefore set forth may be made without departing from the spirit and scope thereof, therefore only suchlirnitations should be imposed as are indicated in the appended claims.
l. A method of fracturing at a predetermined location a subsurface formation penetrated by `a well bore to increase the production of fluid from said formation which comprises introducing a fracturing uid into `said well bore adjacent said predetermined location of said formation tobe fractured, increasing the pressure upon said fracturing fiuid Within said well bore adjacent said predetermined location in order to impose upon said formation at said predetermined location a pressure suhstantially equal to the consolidation pressure of said formation at said location, and explnosively fraoturing said formation at said predetermined location prior to 2,9ss,14a
the fluid fracturing of said formation which would occur when the the pressure applied to said formation at said predetermined location by said fracturing uid reached a Value substantially equal to said consolidation pressure at said predetermined location, thereby explosively initiating the fracture Within said formation at said predetermined location with the result that the thus-pressurized fracturing fluid effects a substantial extension of the thusinitiated fracture outwardly from said well bore into said formation at said predetermined location.
2. A method of fracturing at a predetermined location a subsurface petroleum-producing formation penetrated by a well bore to increase the production of petroleum from said formation which comprises positioning a charge of high explosive in said well bore adjacent said predetermined location, introducing a fracturng fiuid into said Well bore adjacent said predetermined 1ocation of said petroleum-producing formation to be fractured, progressively increasing the pressure upon said fracturing Huid within said Well `bore 'adjacent said predetermined location in order to impose upon said formation at said predetermined location a fluid pressure substantially equal to the consolidation pressure of said formation at said location, `and exploding said high explosive charge just prior to the fluid fracturing of said formation which would occur when the pressure applied to said formation at said predetermined location by said fracturing fluid reached a value substantially equal to the formation consolidation pressure at said predetermined location, thereby explosively initiating a fracture Within said formation at said predetermined location with the result that the thus-pressurized fracturing fluid effects a substantial extension of the explosively initiated fracture outwardly from said well bore into said formation at said predetermined location.
3. A method in accordance with claim 2 wherein said high explosive charge is a shaped charge directed to expel its explosive energy radially outwardly from the well bore into said formation `at said predetermined location.
4. A method in accordince with claim 2 wherein 6 said predetermined location is in the central portion of said petroleum-producing formation.
5. A method in yaccordance with claim 2 wherein said fracturing fluid contains a viscosity-increasing additive material effective to substantially restrict the iiow of said fracturing fluid into said petroleum-producing formation while the pressure exerted upon said fracturing uid is being progressively increased.
6. A method in `accordance with claim 2 wherein said fracturing fluid comprises a crude oil.
7. A method in accordance with claim 2 wherein prior to introduction of said fracturing :uid into said Well bore there is formed at said predetermined location a relatively liquid-impermeable filter cake on the surfaces of said formation exposed by said well bore.
8. The method of fracturing Iat the desired level in a well a formation penetrated by the well comprising detonating a shaped explosive charge forming a substantially planar jet in the plane in which a formation fracture is desired, while simultaneously applying to the formation a hydraulic pressure sufficient to fracture the formation with the aid of the explosion of the shaped charge, but less than the normal fracturing pressure of the formation.
9. A method in accordance with claim 1 wherein prior to the introduction of said fr-aoturing fluid into said Well bore there is formed at said predetermined location a relatively liquid-impermeable filter cake on the surfaces of said formation exposed by said Well bore.
References Cited in the iile of this patent UNITED STATES PATENTS 1,588,643 Alexander June 15, 1926 2,316,596 Kennedy Apr. 13, 1943 2,379,516 Garrison July 3, 1945 2,506,836 Kaltenberger May 9, 1950 2,547,778 Reistle Apr. 3, 1951 2,596,843 May 13, 1952 2,630,182 Klotz Mar. 3, 1953 2,676,662 Ritzmann Apr. 27, 1954