Tertiary recovery operation
nited States Patent [191 ll loyt 1451 Apr. 22, 1975 TERTIARY RECOVERY OPERATION [75] Inventor: Donald L. Hoyt, Houston, Tex.  
 [73] Assignee: Texaco Inc., New York, NY.  
 [22] Filed: Dec. 22, 1972 [21] Appl. No.: 317,580  
 3,332,485 7/1967 Colburn 166/245 3,354,953 11/1967 Morse 3,477,509 11/1969 Arendt 166/245 Primary E.\&#39;aminerFrank L. Abbott Assistant Examiner-Jack E. lEbel Attorney, Agent, or FirmThomas H. Whaley; Carl G. Ries&#39; [57] ABSTRACT Following completion of a secondary recovery operation at breakthrough of the driving flood at the production wells, additional injection wells are located where the oil saturation in the formation is usually higher, usually adjacent production wells with the new injection wells being located between production wells.  
 11 Claims, 5 Drawing Figures PevAz/r/m/v 14 2 22 ,o JfCO/VD/IPY/NJZWO/V 14 544 TERTIARY RECOVERY OPERATION FIELD OF THE INVENTION This invention relates generally to the production of hydrocarbons from subterranean hydrocarbon-bearing formations, and more particularly, to a method for increasing the efficiency of the production of hydrocarbons therefrom.  
 DESCRIPTION OF THE INVENTION In the production of hydrocarbons from permeable subterranean hydrocarbon-bearing formations, it is customary to drill one or more boreholes or wells into the hydrocarbon-bearing formation and produce formation fluids including hydrocarbons, such as oil, through designated production wells, either by the natural formation pressure or by pumping the wells. Sooner or later, the flow of hydrocarbon-bearing fluids diminishes and/or ceases, even though substantial quantities of hydrocarbons are still present in the underground formations.  
  Thus, secondary recovery programs are now an es sential part of the overall planning for exploitation of oil and gas-condensate reservoirs in subterranean hydrocarbon-bearing formations. In general, this involves injecting an extraneous fluid, such as water or gas, into the reservoir zone to drive formation fluids including hydrocarbons toward production wells by the process commonly referred to as flooding.&#34; Usually, this flooding is accomplished by injecting through wells drilled in a pattern, e.g. the alternating line drive and the more commonly used S-spot pattern, which may be visualized as a special type of staggered line drive pattern wherein the separation of the lines of wells is half the spacing between the individual wells.  
  When the driving fluid, e.g. water, from the injection well reaches the production wells of a direct line drive and a staggered line drive, the areal sweep efficiencies are respectively 57 and 78%, and of a -spot pattern, the areal sweep efficiency is about 71%. By continuing production considerably past breakthrough, it is possible to produce more of the remaining unswept portion of the formation, although continued injection will not reduce oil saturation much further.  
 SUMMARY OF THE INVENTION It is an overall object of the present invention to provide an improved recovery procedure involving initially three wells in line as part of a well pattern arrangement for exploiting a hydrocarbon-bearing formation, by locating an additional injection well between production wells in the selected pattern, as determined by model studies or field observation.  
  A three well group is arranged in line so that the intermediate well is completed for injection and the remaining two wells are completed for production. Flooding is initiated at the intermediate well by injection of a driving fluid, such as water, thereinto and proceeds until breakthrough of the flood front occurs at the production wells, at which time, injection via the intermediate well to maintain flooding may be suspended or terminated. Then, one or more additional injection wells aligned with each other and located between the production wells are drilled into the formation and driving fluid is injected via these additional wells to drive formation fluids toward the production wells. In this manner, the formation areas where the highest oil saturation has been determined to be, usually adjacent (or between) the production wells, can be exploited for more complete recovery, this region being unswept by the secondary recovery operation, generally.  
  Other objects, advantages and features of this invention will become apparent from a consideration of the specification with reference to the figures of the accompanying drawings.  
 BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 discloses the symbols used in the remaining figures of the drawing;  
  FIG. 2 illustrates secondary and tertiary phases of a recovery procedure of a direct line drive;  
  FIG. 3 discloses two units of an inverted S-spot pattern, a special form of a staggered line drive, and showing the secondary and tertiary phases of a recovery procedure; and  
  FIGS. 4 and 5 each disclose two units of an inverted S-spot pattern, further illustrating secondary and tertiary phases of recovery procedures.  
  The objects of the invention are achieved by the use of additional injection wells located between production wells where the highest oil saturation is usually located at breakthrough at the conclusion of secondary recovery procedures.  
  The specification and the figures of the drawings schematically disclose and illustrate the practice and the advantages of the invention with different well patterns, examples of which have been observed in potentiometric model studies which simulate secondary and tertiary recovery operations. The model studies indicate a sweep-out obtained in an ideal reservoir, although the recovery from an actual sweep-out of a particular field may be greater or less, depending on field parameters.  
  Throughout the figures of the drawings, the same symbols will be maintained as disclosed in FIG. 1, viz. a solid circle indicates a production well, an open circle with a first&#39;quadrant arrow indicates an original injection well, and an open circle with a fourth quadrant arrow, an additional injection well.  
  Referring to FIG. 2, there is disclosed symbolically a direct line drive in a secondary recovery procedure, wherein the original injection wells are aligned with the production wells. Upon breakthrough of the driving fluid at the production wells, these original injection wells may be put on a stand-by basis till completion of additional injection wells located between the production wells. Then, as driving fluid is injected into the formation via the additional wells, injection via the original wells either may be resumed or terminated. In this figure, the additional injection wells are aligned with each other in rows parallel to the original injection and production wells in the direction of the line drive.  
  In FIG. 3, the invention is illustrated by two units of an inverted 5-spot pattern for a secondary and teritary recovery operation with both the original and additional injection wells being aligned in parallel rows between parallel rows of production wells, the additional wells being located between production wells.  
  FIG. 4 also shows two units of an inverted S-spot pattern, wherein, upon breakthrough of the driving fluid at the comer production wells following the injection of secondary recovery driving fluid via the original injection well in the center of the pattern, the additional injection wells are between and aligned with the corner production wells.  
  FIG. 5, showing two units of an inverted 5-spot pattern, illustrates the combination of the disclosures of FIGS. 3 and 4, with the additional injection wells aligned with the original wells and other additional wells aligned with the rows of corner production wells, the additional wells being located between production wells.  
  Thus, there has been shown and described the manner by which a tertiary recovery operation may be initiated following the conclusion of a secondary recovery operation after breakthrough of driving fluid at the production wells. Tertiary recovery processes can be improved by drilling additional (or using stand-by) wells in regions of high oil saturation. Potentiometric model studies can be useful to determine the optimum locations of new wells. Also, the ratio of tertiary injection to production wells (l/P ratio) is an important economic factor, as it indicates how many new wells may have to be drilled.  
  The table below is a summary of results at breakthrough of tertiary injection fluid.  
 Ratio of Injection to Sweep Efficiency &#34;/1 Production Wells As will be apparent to those skilled in the art in the light of the accompanying disclosure, other changes and alterations are possible in the practice of this invention without departing from the spirit or scope thereof.  
 I claim:  
  1. In a method of recovering petroleum from a subterranean, petroleum containing formation, said formation being penetrated by at least one initial injection well and by at least two production wells, said formation having been exploited by means of an oil recovery method of the type in which an extraneous drive fluid is injected into the injection well to displace petroleum toward the production wells, the improvement which comprises:  
 penetrating said formation after breakthrough of the extraneous drive fluid at the production wells with at least one additional injection well drilled into a portion of the formation having a higher oil saturation than that portion immediately adjacent to said initial injection well, and  
 injecting into said second injection well, after breakthrough of the extraneous drive fluid injected into the initial injection well at the production wells, an extraneous drive fluid to displace additional formation fluids toward the production wells.  
 2. A method as recited in claim 1 wherein said initial injection well and said additional injection well are drilled at essentially the same time and said additional injection well is held in standby during the period when extraneous drive fluid is injected into said initial injection well.  
  3. A method as recited in claim 1 wherein said initial injection well is shut in after initiating injection of extraneous drive fluid into the additional injection well.  
  4. A method as recited in claim 1 wherein injection of extraneous drive fluid into the initial injection well is continued after initiating injecting extraneous fluid into said additional injection well.  
  5. A method as recited in claim 1 wherein the formation is penetrated by a plurality of initial injection wells and by a plurality of production wells and said secondary recovery method comprises a line drive.  
  6. A method as recited in claim 1 wherein the formation is penetrated by a plurality of initial injection wells and by a plurality of production wells and said secondary recovery method comprises a S-spot pattern.  
  7. A method as recited in claim 1 wherein said formation is penetrated by at least two production wells and said additional injection well is located between said production wells and closer thereto than said initial injection well.  
  8. A method as recited in claim 1 wherein said formation is penetrated by at least one initial injection well and by four production wells located in 5-spot configuration around each initial injection well. and at least one additional injection well is located between adjacent production wells and closer thereto than the initial injection wells.  
 9. A method as recited in claim 1 wherein the extraneous drive fluid is water.  
  10. A method as recited in claim 1 wherein the extraneous drive fluid is gas.  
  11. In a method of recovering petroleum from a subterranean, petroleum containing formation, said formation being penetrated by at least one initial injection well and by at least two production wells, said formation having been exploited by means of an oil recovery method of the type in which an extraneous drive fluid is injected into the injection well to displace petroleum toward the production wells, the improvement which comprises:  
 penetrating said formation with at least one additional injection well drilled into a portion of the formation having a higher oil saturation than that portion immediately adjacent to said initial injection well, said additional injection well being drilled into the formation after breakthrough of the extraneous fluid at said production wells, and injecting into said second injection well, after breakthrough of the extraneous drive fluid injected into the initial injection well at the production wells, an extraneous drive fluid to displace additional formation fluids toward the production wells.