US3452816A - In situ combustion method - Google Patents

Description

CONDENSATION ZONE DISTANCE w c. HARDY L IN SITU COMBUSTION METHOD Filed Dec. 15-, 1967 CONDENSATION ZONE DISTANCE ww In mDOmDG mIP 2.

July 1, 1969 COMBUSTION ZONE TEMPERATURE TEMPERATURE AMBIENT ZONE TEMPERATURE COMBUSTION ZONE FIG. 3

United States Patent US. Cl. 166256 7 Claims ABSTRACT OF THE DISCLOSURE The particular embodiment described herein as illustrative of one form of the invention utilizes'a method for applying in situ combustion techniques to formations having a high gravity crude oil, which method involves the generation of a combustible fuel in the formation by the addition of acids to the formation. The mixture of acid and crude oil produces an acid sludge, with the order of the reaction being increased by elevated temperature. The combustion of such an acid sludged fuel will liberate water and acid gases. These products will flow as a mixture to cooler regions of the reservoir where condensation and absorption takes place to form a regenerative cycle of acid.

Background of the invention This invention relates to a method for recovery of hydrocarbons from oil bearing formations, and has particular reference to recovery processes involving in situ combustion of high gravity crude oil.

Various methods of applying heat to an oil reservoir are known, however, the forward burn technique is the most common and the process set forth in this-disclosure will be described in terms of the forward burn. The forward burn consists principally of (1) flowing air through an oil reservoir from an injection well to a producing well, (2) igniting the oil around the injection well by some convenient method such as electrical heater, gas burner or chemical reaction, and (3) continuing the injection of air to propagate a combustion zone through the oil reservoir from injection to producing wells. Low gravity crude oils, particularly those ranging between and API, appear to afford little ditficulty in the in situ combustion process in that a proper accumulation of fuel is maintained for the encroaching combustion front. High gravity crude oils, on the other hand, generally have low viscosities and low boiling ranges and therefore tend to be displaced by the heat of the combustion taking place in the formation thereby presenting an insufficient accumulation of fuel to the encroaching combustion front. These oils, ranging, for example, from to API, generally do not naturally contain sufficient heavy fractions to fuel the forward combustion process. Although this type of oil generally water floods fairly well, frequently large volumes remain in the reservoir as residual.

It is therefore an object of the present invention to provide a new and improved method of in situ combustion in high gravity crude reservoirs by thickening a small fraction of the oil to convert it to fuel for supporting the combustion necessary to produce the balance of hydrocarbons in the reservoir.

Summary of the invention With these and other objects in view, the present invention contemplates a method for recovering hydrocarbons from a formation by in situ combustion where the formation contains high gravity crudes, including adding or generating an acid in the formation which when contacted with the high gravity crudes forms a petroleum sludge. Such sludge acts as a fuel to support the in situ combustion process. Air and heat are applied to the formation to ignite the sludge. Acid gases and water vapor are liberated from the combustion process and migrate with the air flow to cooler regions of the formation where condensation of the acid gas and water produces an acid which, in turn, forms a regenerative cycle of acid sludge. The initial introduction of acid to the formation may be in the form of an acid, an acid forming gas, a petroleum product containing compounds capable of generating an acid or acid gas, or any other material which will produce an acid when combined with materials in a petroleum formation under the conditions of an in situ combustion process.

A complete understanding of this invention may be had by reference to the following detailed description when read in conjunction with the accompanying drawings.

A brief description of the drawing FIGURE 1 is a diagram, in the form of a vertical section illustrating a portion of an oil reservoir to which the invention is applied;

FIGURE 2 is a plot of temperature versus distance to the horizontal scale of FIGURE 1, explanatory of the type of problem which exists and which it is the object of the present invention to solve; and

FIGURE 3 is a plot similar to FIGURE 2 illustrating the variation of hydrogen ion concentration in the aqueous phase of a well versus distance.

Description of the preferred embodiments Referring first to FIGURE 1, one or more injection Wells are indicated at 12, provided with control valves 14, and penetrating at their lower end 16, a hydrocarbon containing formation indicated at 18. Spaced from the injection wells are production wells 20 illustrated as having control valves 22, which wells penetrate the same formation at 24. It will be understood that while these wells are merely diagramed, they may be arranged and spaced in accordance with well known practices which need not be described in detail here since they have no bearing on the essential aspects of the present invention. The production wells may, of course, be pumped if re quired. The wells are also located relative to one another in accordance with conventional practices depending upon knowledge of the producing formation, this knowledge being secured by preliminary conventional production, by the drilling of test holes, by core sampling, et cetera. In brief, the arrangement of wells is adapted to secure, ultimately, maximum recovery with minimum cost. It might be stated, as a summary, that the locations are such as to secure a sweeping of desired products from a maximum region consistent with the above burning procedure.

Considering the wells indicated in FIGURE 1, a formation between the injection well or wells and the production well or wells, in which in situ combustion is progressing, contains identifiable zones, though the boundary of transition from one zone to the next may not be sharply defined; in fact, they may be quite indefinite. From the standpoint of consideration of the present invention, the zones which would exist in the ordi nary forward combustion procedure, after burning had been initiated, to some extent would be as generally illustrated in FIGURE 2. First, in the vicinity of the injection well or wells there would 'be a burned zone indicated at 26. Following this, in the direction of flow, there is a combustion zone indicated at 28, a condensation zone indicated at 32, and finally the unaltered zone 34. The burned zone contains approximately of the range in temperature up to 1000 degrees F. The combustion zone may range from 550 degrees F. to 1200 degrees F., depending upon the type and amount of fuel deposited by the oil on the reservoir rock. The condensation zone which actually controls the entire process may be viewed as three subzones; subzone 36 containing high viscosity distillation residue, subzone 38 containing a high water saturation and residual oil, and subzone 40 containing the oil bank. It is apparent, that in order to propagate a forward in situ combustion process, there must be an accumulation of hydrocarbon in subzone 36 which will furnish fuel for the encroaching combustion front. High gravity crude oils, which generally have low viscosities and low boiling ranges tend to be readily displaced from this zone thereby causing an insuificient accumulation of oil for fuel in subzone 36.

Crude oil in which the ordinary combustion process is sufiiciently operative has been found to exhibit particular physical properties. Those properties which have been found to thus distinguish between crude oils which are or are not susceptible to forward combustion processes are the average volumetric boiling point (A.V.B.P.) and the viscosity at 350 degrees F. Crude oils whose average volumetric boiling point (A.V.B.P.) viscosity (350 F.) product exceeds 350 F. C.P. will generally propagate in situ combustion process. Crude oils whose (A.V.B.P.) viscosity product is less than 350 F. C.P. have been found incapable of or very inefficient in propagating a forward in situ process.

It is well known that the combustion of crude oil in air will give rise to the production of water, combustion gases such as CO and CO oxides of sulphur, oxides of nitrogen, oxygenated hydrocarbon, plus organic and inorganic acids. In the forward in situ combustion process, these products flow from the combustion zone to cooler regions of the formation where they are condensed and/or sorbed from the vapor phase. The presence of the oxides of carbon, sulphur, and nitrogen in addition to water causes the formation of inorganic acids such as carbonic acid, sulphuric acid and nitric acid downstream from the combustion zone. Analysis has shown that in addition to inorganic acids, organic acids such as formic, acetic, propionic, butyric, valeric, caproic and others up to ten carbon molecules are also found in condensed products of combustion. In addition to fatty acids, the combustion products have been shown to contain hydroxy acids, lactones, anhydrides, phenols, naphthenic acids, alcohols, .aldehydes, ketones, and esters.

That the presence of organic and inorganic acids in the products of combustion are formed by condensation or sorption of the combustion products can be indicated by the hydrogen ion concentration or pH of the produced water from the in situ combustion process. FIGURE 3 shows a typical curve of pH versus distance, of the water contained in the formation which hosts in the in situ combustion process. FIGURE 3 shows that the pH of the water in the ambient zone 34 should be very near that of the original water in place. This value will vary, depending upon the salts in solution; however, the original water in place is generally slightly acid. The water in the condensation zone 32 of the in situ combustion process has been found to have an average pH of approximately three. This value corresponds generally to the pH of carbonic acid resulting from the solution of CO in water. As the combustion zone 28 is approached, it has been found that the pH of the water in the in situ combustion process drops to a value as low as 1.0 or lower. This property of the water indicates a concentration of fairly strong organic and/or inorganic acids.

In the processing of crude petroleum oils, especially in refining, it is generally known that the mixing of oil with various organic and inorganic acids will produce a sludge which will precipitate from the oil. Especially well known is the de-asphalting process which consists of the admixture of concentrated sulphuric acid and crude oils. Also, the sludging of even refined lubricating oils can be observed in the crankcases of internal combustion engines, due to its contamination with acids manufactured by the combustion of gasoline in the engines cylinders. It is also known that in certain formations, following acidizing treatments, the Wells have been very slow to clean up, and often .a great deal of asphalt like material has been recovered with the treating fluids. In some cases, complete or partial plugging of the wells has resulted from the treatment. The study of the problem has revealed that the crude oils produced from such wells actually for-m solid precipitates upon contact with the acid. These precipitates were mainly asphaltenes, resins, paraffin waxes, and other high molecular weight hydrocarbons. Experiments have shown that the sludges formed from crude oil by .acid treatment are generally sticky and characterized by high viscosity, high molecular weight, and relatively low ignition temperatures.

It has been found by experiment that fuel consumed in the in situ combustion process is, in part, manufactured in situ by the sludging of certain components of the crude oil when reacted with the complex acids resulting from combustion. The mechanism of sludging a crude oil with acid is not entirely understood, however, others have shown (Petroleum Refinery Engineering by W. L. Nelson, McGraw-Hill, 1949, chapter 12) that sulphuric and nitric acids will react with oil to remove nitrogen, sulphur, and oxygen based compounds. These acids will react readily with unsaturated hydrocarbons. In their order of reactivity, the following compounds commonly found in crude oil will produce acid sludges: (1) asphaltic compounds, (2) olephenic compounds, (3) aromatic compounds, and (4) naphthenic compounds. Parafiins have been found to react very slowly with most acids to 'produce acid sludges. The mechanisms which produce acid sludges from the admixture of various acids and crude oil are, amongst others: (1) the decrease in solubility of polar, heterohydrocarbon compounds containing nitrogen, sulphur, and oxygen. Asphaltenes .are composed of such compounds. For example, the precipitation of asphaltenes in high pH environments appears to be related to decreased solubility of polar nitrogen containing compounds; (2) reaction of acids with unsaturated hydrocarbons to produce polymers, aldehydes, organic acids, and other oxidation products; (3) dissolution of naphthenic acids and basic nitrogen compounds; (4) sulfonation and nitration of hydrocarbons to produce, for example, alkyl, aryl, and naphthenic acids, sulfonates, nitrates, acid esters, etc. The order of these reactions is increased by elevated temperature.

Combustion of such petroleum acids has been shown to produce combustion products such as CO S0 S0 N 0, NO, N0 and other acid gases. These gases when contacting water can be absorbed to form nitric, sulphuric, and carbolic acids. Crude oils that do not deposit suflicient fuel on the reservoir rock to sustain the forward in situ combustion process also produce only trace amounts of organic and inorganic acid gases because insuflicient burning takes place, thus leaving a high percentage of oxygen and a low percentage of combustion gas. On the other hand, crude oils which do deposit sufiicient fuel on the reservoir rock to sustain the forward in situ combustion process, also produce a significant amount of acid gases and organic acids. Crude oils which have high in situ combustibility tend to be naphthenic and crude oils which have low in situ com bustibility tend to be parafiinic. It is generally known that parafiinic crude oils will produce relative low volumes of acid sludge.

In order to determine the applicability of acid sludging and subsequent in situ combustion of a reservoir containing high grade crude oils, a combustion tube test was conducted to simulate such .a process. The combustion tube test utilized a 42 inch long, thin wall, 5 inch outside diameter stainless steel tube packed with a mixture of graded sand, clay, water, and crude oil mixed in the desired weight ratio. The packed tube was assembled with an electrical ignitor adjacent the sand face at one end of the tube. The assembled combustion tube was inserted in a reactor chamber to permit its operation at high pressures without creating a pressure differential across the walls of the tube. For the test, 26 cylindrical guard heaters each approximately one and one-half inches wide were placed about the combustion tube to provide for operation at near adiabatic conditions. Provision is made for separation of produced liquids .and gases. The combustion tube test is initiated by establishing air flow at a controlled rate of injection pressure through the tube. Ignition of the oil sand is effected by energizing the electrical ignitor and controlling its temperature to a preset value. The combustion front is propagated through the tube by continuous injection of air. The efiiuent gas is analyzed and its volume is measured. A thermocouple well contains twenty-six thermocouple junctions arranged to sense the temperature 1 /2 inch intervals along the length of the tube. This thermowell is placed in the center of the combustion tube before packing the tube.

After ignition of the oil sand, the high temperature combustion zone moves down the combustion tube. Temperature changes along the tube are sensed by the thermocouples in the center thermowell and compared with the temperature of the guard heater to thereby control the guard heater system and maintain the individual heaters at the same temperature as that indicated by the corresponding thermocouple in the combination tube. The temperature is sequentially measured along the tube and this parameter is recorded automatically to provide data for temperature profiles of the combustion tube at any time. Pressure measurements and profiles are also made on the test. The eflluent gas is continuously analyzed by an oxygen analyzer and a series of thermal conductivity cell analyzers. Chromatograph analysis is also run on the efliuent gas to determine the contents of the combustion gas.

Such a combustion tube test, together with bench tests shows that characteristic behavior of crude oils and components of crude oils when admixed with certain acids can be used to cause the deposition of suflicient fuel in .a petroleum reservoir to sustain the forward in situ combustion process. Such characteristic behavior may be the action of sulphuric acid with the aromatic, olefinic, naphthenic, and asphalt components of crude oils to precipitate a sludge containing asphaltenes and various reaction products such as alkyl, aryl, and naphthenic sulfonates, acids, aldehydes, alcohols, and esters.

The .above described behaviors may be applied to petroleum reservoirs, using several techniques, to increase oil recovery by the forward in situ combustion process. One such technique is described as follows: A flow of air through the strata of a hydrocarbon bearing reservoir is established by injecting air through one or more injection wells and returning a portion of the air to the surface through one or more producing wells. A slug of acid is then introduced into the injection well which, together with a continued air flow, causes the flow of the acid into the petroleum reservoir. The intimate mingling of the acid and crude oil within the interstices of porous media will cause a sludge to precipitate from the oil and stick to the walls of the porous media. Heat is then applied to the reservoir by any well known means to ignite the sludge formed therein and thereby initiate combustion of the reservoir. The acid injected could be one or a combination of organic or inorganic types of acid. Tests have shown that commercial grade concentrated sulphuric acid, red fuming nitric acid, white fuming nitric acid, certain organic acids, halogenated organic acids, and combinations of such acids will produce satisfactory sludging of crude oil. The type of acid used would depend to a great extent on the type of crude oil involved, with some crudes being more effectively sludged by certain types of acid. The specific type of acid needed in a forward in situ combustion process can easily be determined by simple laboratory tests simulating the reservoir conditions.

The volume of the acid slug which would be injected into a reservoir to cause sludging of the crude oil has been found in laboratory experiments to range between .5 and 5 percent of the recoverable oil in the reservoir.

However, all classes of crudes and acids have not been combined to determine the optimum percent by volume which would be needed for the various types, and therefore these percentages should not be considered as limiting factors, but rather as indicative of a range which may be applicable to individual situations. Since the formation of the petroleum sludge is an acid reaction process, the combustion of the sludge will liberate water and acid gases such as CO S0 S0 N 0, NO, and N0 upon combustion in the presence of oxygen. These products will, in turn, flow as a mixture to cooler regions of the reservoir, that is the condensation zones where condensation and sorption take place to create a regenerative cycle of acid production. The regenerated acid immediately reacts with new oil in the reservoir to produce a petroleum sludge on which the forward in situ combustion process is sustained.

An alternative process which utilizes the same concepts as the process described above, is as follows: in conjunction with the steps of injecting air into the reservoir, igniting hydrocarbons in the reservoir and producing the reservoir from a production well; where high gravity crude oils are found, a fuel gas is injected into the reservoir simultaneously with the injection of air which when reacted with air by combustion will produce an acid gas. An example of such a gas is hydrogen sulphide, which will react with oxygen to produce S0 and S0 The fuel gas can be burned either in the injection well or in the formation during and subsequent to ignition. The acid gas resulting from the combustion of the fuel gas will flow to cooler regions of the formation where it condenses and combines with water in the formation to form an acid which, in turn, establishes the regenerative cycle of acid sludge described previously.

A third technique involving principles of the present invention is also applied in conjunction with the steps of flowing air into a formation, igniting the formation, and recovering production at a recovery well. This technique includes injecting a slug of crude oil into the well prior to the application of heat for ignition. The crude oil should have a relatively high percentage of oxygen, sulphur, and/or nitrogen compounds. The presence of such compounds under combustion conditions will cause a natural production of an acid fuel sludge to support a forward in situ combustion process. Again, combustion of such fuel sludge will produce acid gases and water which, upon flowing to cool regions of the formation will condense to form acid and consequently, a regenerative cycle of acid sludge as previously described.

In summary, the processes described above permit the propagation of a forward in situ combustion process in reservoirs containing high gravity crude oil. The mechanism which is fundamentally important in the process is the in situ production of an acid addition petroleum sludge which is retained on the walls of the porous media of the formation and becomes a fuel to sustain the forward in situ combustion process. The acid addition petroleum sludge can be produced by an admixture of an acid and crude oil. Combustion of these petroleum sludges produces an acid gas, which upon flowing to cooler regions of the reservoir is contacted with water to establish a regenerative cycle of acid. Several techniques have been described for practically applying this method of contacting high gravity crude oil in the reservoir with one or more acids, acid gases, combustion products of certain fuel gases and/or combustion prodnets of crude oils which would naturally contain acid gases, especially oxides of sulphur and nitrogen. The particular technique used will depend upon such factors as reservoir conditions, availability of the fuel involved in each technique, and the type of crudeoil in the reservoir.

While particular embodiments of the present invention have been shown and described, it is apparent that changes and modifications may be made without departing from this invention in its broader aspects, and therefore, the aim in the appended claims is to cover all such changes and modifications as fall within the true spirit and scope of this invention.

What is claimed is:

1. A method for the production of hydrocarbon materials from a formation penetrated by at least two wells and containing high gravity petroleum hydrocarbon deposits which includes: injecting air and an acid through one of the wells into the formation, which acid forms a sludge with at least a portion of the hydrocarbon deposits in the formation; applying heat from an external source to the sludge formed in the formation while continuing the injection of air into the formation to initiate combustion of the sludge; ceasing the application of heat from such external source while continuing the injection of air to support a regenerative cycle of combustion of such sludged material; and recovering hydrocarbons liberated by such combustion from the other well.

2. The method of claim 1 in which the amount of acid injected is sufficient to generate a sludge that will support a regenerative cycle of radial combustion throughout the formation between the wells.

3. The method of claim 1 in which combustion of the sludge material liberates an acid gas and water vapor which condenses when contacted with cooler zones of the formation to form an acid which, in turn, reacts with the high gravity petroleum deposits to form a combustible sludge and thereby produce a regenerative cycle of combustion.

4. A method of production'of hydrocarbon materials from a formation penetrated by at least two wells and containing high gravity petroleum deposits, which includes: injecting air through one of the wells into the formation; while continuing the injection of air introducing a slug of inorganic acid into the one well for contacting the acid with such high gravity petroleum products to form a petroleum acid sludge material in the formation; introducing a temporary supply of heat to the sludge material while continuing the injection of air to ignite the sludged material; discontinuing the supply of heat while continuing the injection of air to support a regenerative cycle of acid sludging and combustion in the formation; and recovering hydrocarbon materials liberated by the combustion from the other well.

5. A method for the production of hydrocarbon materials from a formation penetrated by at least two wells and containing high gravity petroleum deposits, which includes: applying heat to the formation through one of the Wells; injecting air and a fuel gas into the one well, which fuel gas contains a substantial amount of acid forming elements that will form an acid gas when reacted with air by combustion, such acid gases forming an acid when combined with water in the well and formation to produce a petroleum acid sludge material in the formation; discontinuing the injection of fuel gas while continuing the injection of air to support a regenerative cycle of sludging and combustion of the sludged material; and producing hydrocarbon materials liberated by such combustion from the other well.

6. The method of claim 5, in which combustion of the sludged material liberates an acid gas which condenses when contacted with cooler zones of the formation and combines with water in the formation to form an acid which, in turn, reacts with the high gravity petroleum deposits to form a combustible sludge and thereby form a regenerative cycle.

7. A method for the production of hydrocarbon materials from a formation penetrated by at least two wells and containing high gravity petroleum hydrocarbon deposits, which includes: injecting air and a slug of crude oil through one of the wells into the formation, where the injected crude oil contains a relatively high percentage of compounds for forming an acid when reacted with air by combustion and water in the formation, such acid forming a combustible acid sludge material when contacted with high gravity petroleum hydrocarbon deposits; applying heat to the sludge material while continuing the injection of air to ignite and burn the sludge material, the combustion of the sludged material liberating an acid gas which condenses after flowing to cooler regions of the formation and combines with water to form a regenerative acid which, in turn, combines with new high gravity hydrocarbon deposits to form a combustible acid sludge and thereby sustain burning throughout the formation; and recovering hydrocarbons liberated by the 'burn ing from the other well.

References Cited UNITED STATES PATENTS 2,863,510 12/1958 Tadema et al. 166-39 X 2,889,881 6/1959 Trantham et al. 16611 3,064,728 11/1962 Gould 166-11 X 3,233,671 2/1966 Chatenever 16611 3,263,750 8/1966 Hardy 16611 3,400,760 9/ 1968 Orkiszewski 16611 STEPHEN J. NOVOSAD, Primary Examiner.

US. Cl. X.R.

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