Tertiary recovery operation
United States Patent [191 Altamira et al.  
 [451 Apr. 15, 1975 TERTIARY RECOVERY OPERATION [75] Inventors: Anthony F. Altamira, Dhahran,  
 Saudi Arabia; Donald L. Hoyt,  
 Houston, Tex.  
 [73] Assignee: Texaco Inc., New York, NY.  
 [22] Filed: Apr. 8, 1974 21 Appl. No.: 458,918  
 Primary Examiner-Stephen .1. Novosad Attorney, Agent, or FirmThomas H. Whaley; Carl G. Ries [57] ABSTRACT At the conclusion of a secondary recovery operation in a direct line drive, after breakthrough of the driving fluid at the production wells in alternate series of a pair of production wells and an intermediate injection well having a different rate of injection of driving fluid, production is continued via the wells in the remainder of alternate series until breakthrough, and  
 thereupon, for tertiary recovery, by the imposition of a new set of flow gradients, the original injection wells are shut in, the production wells with the initial breakthrough are converted into injection wells and production is continued via the remainder of the production wells.  
 5 Claims, 6 Drawing Figures PATENTEDAPR 1 SW5 3. 877, 521  
 SHEET 1 15 g 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 subterranean formations.  
  Thus, secondary recovery programs are now an essential 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 or other displacing compounds, into the reservoir zone to drive formation fluids including hydrocarbons toward production wells by the process commonly referred to as floodingf Usually, this flooding is accomplished by injecting through wells drilled in a pattern, e.g., the direct and alternating line drive and the more commonly used 5-spot pattern.  
  When the driving fluid, e.g., water from the injection well reaches the production wells of a direct line drive, the areal sweep efficiency is 57%. 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.  
  In secondary recovery programs, sweepout is generally given as the percent of available volume invaded by the driving fluid at breakthrough into the production wells. This is done because production past breakthrough, while nearly always attempted, is an uncertain thing. For example, assuming water to be the driving fluid, the water-oil ratio may rise gradually over a period ofmany years or a well or pattern may go to 100% water within months. Much depends on how easily and quickly the water phase envelops the well to such an extent that the relative permeability to oil is reduced to zero.  
  One of the reasons for the rapid rise in water production is that the driving fluid, e.g., water, in reaching the production well, has opened channels through which the water flows preferentially, thereby by-passing much inplace hydrocarbons, such as oil. Continued flow widens&#39;the channels, stripping some of the adjoining hydrocarbons or even opens up a few more channels, but it is observed generally that a large quantity of additional driving fluid, e.g., water, is required to produce ever decreasing amounts of hydrocarbons.  
  A procedure to provide for better recovery more quickly than in the present procedures involves the changing of direction of the flow gradients shortly after breakthrough. A simple and effective procedure after initial breakthrough is to switch the injection of driving fluid to a converted production well offset from the line between an injection well and an adjacent production well. The original injection well having been shut in, the new flow paths established from the converted production well, crossing established water channels, break them up and move trapped or bypassed hydrocarbons toward the other production well.  
  In addition, the driving fluid injected from the converted production well will be sweeping through a region between original production wells which is nearly always of higher hydrocarbon saturation than the region existing between the original injection and production wells.  
  From a potentiometric model study, by continued production past breakthrough of a secondary recovery program in a direct line drive, using the same injection and production wells, the sweepout can eventually approach 95% if the well continues to produce. However, in an actual hydrocarbon reservoir, the cusp of the driving fluid swells so rapidly in this case that the wateroil ratio rises very quickly to over 90%. By this time the water saturation around the well will be so high that continued flow of the oil phase is very unlikely and the pattern may have to be abandoned at about total sweepout.  
  With the intermediate injection wells of the series of the line drive pattern of wells being closed in and the alternate production wells of the adjacent series of wells being converted to injection wells, the interface positions at breakthrough of driving fluid from the converted wells shows that the cusp of previously injected fluid is still small, and the water-oi] production ratio by calculations based on shape is about 25%, and the pattern sweepout is now 92%. This principle of imposing new flow gradients by changing the functions of certain wells can be applied in virtually any reservoir whether drilled on a pattern or not.  
 SUMMARY OF THE INVENTION It is an overall object of the present invention to provide an improved recovery procedure involving three wells in line as one of a series in a direct line drive as part of a well pattern arrangement for exploiting a hydrocarbon-bearing formation with alternate series of wells having different rates of injection, by shutting in the intermediate injection wells following breakthrough of the driving fluid at all of the production wells, thereafter converting the production wells in alternate series of the pattern suffering breakthrough into injection wells while maintaining production from the remainder of the wells of the series.  
  A three-well group of a series in a direct line drive 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 at different rates in alternate series, and proceeds until breakthrough of the flood front occurs at all of the production wells, at which time injection via the intermediate wells is terminated and the wells shut in. Then, the original production wells in the alternate series with initial breakthrough are converted to tertiary injection wells while the remainder of the production wells, viz., those in the other alternate series, are maintained on their original function.  
  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 the principle of the invention;  
  FIGS. 3 and 4 illustrate the first and second phases of a secondary recovery program of a direct line drive;  
  FIG. 5 discloses the termination of the tertiary phase of a direct line drive recovery procedure according to this invention; and  
  FIG. 6 discloses the differences in water cuts during production past breakthrough of a direct line drive and a cross flood line drive.  
  The objects of the invention are achieved by shutting in all of the intermediate injection wells at time of the breakthrough of the driving fluid at all of the production wells in the alternate series having the lower rate of injection thereof and converting the production wells in these alternate series with the initial breakthrough of the driving fluid into injection wells to produce a new set of flow gradient forces to inhibit cusp expansion at the remainder of the production wells in the other alternate series.  
  The specification and the figures of the drawings schematically disclose and illustrate the practice and the advantages of the invention, examples of which have been observed in potentiometric model studies. which simulate secondary and tertiary recovery operations. The model studies indicate a sweepout obtained in an ideal reservoir, although the recovery from an actual sweepout 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, a crossed open circle a shut-in well, an open circle with a first quadrant arrow indicates a low quantity secondary injection well, a double open circle with a first quadrant arrow indicates a high quantity secondary injection well, and an open circle with a fourth quadrant arrow, a converted tertiary injection well.  
  FIG. 2 illustrates the manner of changing the direction of the flow gradients shortly after breakthrough of the driving fluid at a production well. Thereupon, the original injection well is shut in, since channels for the flow of the driving fluid have been established, and the direction of the flow gradients is changed by switching the injection of the driving fluid to a converted production well, offset from the line between the original injection well and the production well with breakthrough. The indicia in this figure are self-explanatory of the phenomenon desired.  
  Referring to FIG. 3, there is disclosed symbolically the first phase of a direct line drive in a secondary recovery procedure, wherein in each series, the intermediate injection wells are aligned with the production wells with a d/a of l, and the production and/or injection rates are such that those production wells in a line substantially perpendicular to the line between the intermediate injection wells and the production wells in each series, will experience breakthrough in alternate series with a sweep efficiency of 57% in each pattern unit (of area 2 da).  
  Referring to FIG. 4 and following breakthrough as indicated by the cusp formations in FIG. 3, all the production wells in the series of the direct line drive program are maintained on production, and as indicated in this figure, the injection of the driving fluid is at an equal rate until breakthrough occurs at the production wells in the other alternate series of the program.  
  Thereafter, as indicated in FIG. 5, all of the intermediate injection wells are shut in, the production wells in the alternate series which had undergone the original breakthrough of the driving fluid are converted to injection wells, and the remaining production wells in the other alternate series remain on production, as either secondary or tertiary driving fluid is injected into the formation via the converted production wells, until the calculated sweepout of the overall pattern has reached about 92%, as disclosed in FIG. 6. This figure discloses that with the cross flood, the water cut decreases with an increase in sweep efficiency to more than 92%.  
  Thus, there has been shown and described the manner by which a tertiary recovery operation may be initiated with favorable economic results following the conclusion of a secondary recovery operation following breakthrough of driving fluid at the production wells, by introducing a new set of flow gradients to affect cusp formation and to displace hydrocarbons otherwise trapped in flow channels established by prior flow graclients.  
  As will be apparently 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.  
 We claim:  
  1. During a recovery operation, a method of producing formation fluids including hydrocarbons from a subterranean hydrocarbon-bearing formation by a direct line drive which comprises penetrating said formation with a plurality of wells disposed in a linear pattern and comprising a series of a pair of production wells and an intermediate injection well, injecting an extraneous driving fluid into said formation via the intermediate injection well to displace formation fluids including hydrocarbons in said formation toward said production wells, producing said formation fluids including hydrocarbons from said formation via said production wells, said producing of said formation fluids and said injecting of said extraneous fluid being at such rates that the production wells in alternate series of wells of said pattern undergo breakthrough of said extraneous fluid initially, thereafter continuing producing said formation fluids while injecting said extraneous fluid until breakthrough of said driving fluid at the production wells in the series of wells alternate to those which had undergone breakthrough initially, thereupon initiating an additional recovery operation by imposing a new set of flow gradients comprising the steps of shutting in the intermediate injection wells in said series and converting production wells in said series which had undergone breakthrough of said driving fluid initially into injection wells, and thereafter producing formation fluids via the remainder of said production wells.  
  2. In the method as defined in claim 1, said intermediate injection well and said pair of production wells being disposed in a common row of a series thereof.  
  3. In the method as defined in claim 2, said intermediate injection well and said production wells being disposed respectively in common rows.  
 LII  
  6 troducing said driving fluid via said intermediate injection wells being equal and the rate of producing formation fluids via said production wells being maintained at a constant rate following the initial breakthrough of said driving fluid at said alternate series of wells.