Tannin materials as additives in oil recovery processes involving chemical recovery agents

A process for producing petroleum from subterranean formations is disclosed wherein production from the formation is obtained by driving a fluid from an injection well to a production well. The process involves injecting via the injection well into the formation an aqueous solution of tannin as a sacrificial agent to inhibit the deposition of surfactant and/or polymer on the reservoir matrix. The process may best be carried out by injecting the tannin into the formation through the injection well ahead of or mixed with either a polymer, a surfactant solution and/or a micellar dispersion. This mixture would then be followed by a drive fluid such as water to push the chemicals to the production well.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
This invention relates to the recovery of oil from subterranean formations 
by chemical flooding methods. 
2. Description of the Prior Art 
Petroleum is frequently recovered from subteranean formations or reservoirs 
by permitting the natural energy of the reservoir to push the petroleum up 
through wells to the surface of the earth. These processes are referred to 
as primary recovery methods since they use the natural energy of the 
reservoir. However, a large amount of oil, generally in the range of 
65-90% or more, is left in the subterranean formation at the conclusion of 
the primary recovery program. When the natural energy is unable to produce 
more petroleum, it is a common practice to resort to some form of 
supplemental recovery technique in order to recover additional petroleum 
left in the subterranean formation. These supplemental operations are 
normally referred to as secondary recovery operations. If this 
supplemental recovery operation is the second in a series of such 
operations, it will be referred to as a tertiary recovery operation. 
However, the terminology is unimportant for the purposes of this 
application and relates only to the sequence in which they are carried 
out. 
The most widely used supplemental recovery technique because of its ease of 
implementation and low capital outlay is water flooding through injection 
wells drilled into the subterranean formation. In a water flooding 
operation, the injected fluid displaces oil through the formation to be 
produced from the injection well. A major disadvantage to water flooding, 
however, is its relatively poor displacement efficiency largely due to the 
fact that water and oil are immiscible at reservoir conditions and high 
interfacial tension exists between the flood water and the oil. For this 
reason, after a water flood, a large portion of the oil is still left 
unrecovered in the reservoir. 
It has been recognized by those skilled in the art that a solution 
effecting a reduction in this interfacial tension between water and oil 
would provide a much more efficient recovery mechanism. Therefore, the 
inclusion of a surface active agent or surfactant in the flood water was 
recognized as an acceptable technique for promoting displacement 
efficiency of the reservoir oil by the water. For example, U.S. Pat. No. 
3,468,377 discloses the use of petroleum sulfonates in water flooding 
operations and U.S. Pat. No. 3,553,130 discloses the use of ethylene oxide 
adducts of alkyl phenols for the same purpose. The use in water flooding 
operations of water soluble surface active alkaline earth resistant 
polyglycol ethers is disclosed in U.S. Pat. No. 2,233,381. Other 
specialized surfactants, as will be discussed later, have been discovered 
to have special properties useful in water flooding operations such as a 
tolerance for high salinity and calcium, and/or magnesium ion 
concentrations often found in reservoir waters. 
However, field operations employing surfactants and surface active agents 
in injected fluid have not always been entirely satisfactory due to the 
fact that these materials are often adsorbed by the formation rock to a 
relatively high degree, resulting in an ever declining concentration of 
the materials as they progress through the reservoir. Therefore, large 
concentrations of surface active materials have heretofore been necessary 
to maintain a sufficient concentration at the oil-water interface. Due to 
this, many proposed flooding operations involving surface active materials 
have been uneconomical. 
Another serious problem for any recovery technique involving the driving of 
oil with a fluid is premature breakthrough of the injection fluid. This 
premature breakthrough indicates that the reservoir has not been 
adequately swept of oil. The problem is often described in terms of sweep 
efficiency as distinguished from the displacement efficiency described 
above. Displacement efficiency involves a microscopic pore by pore 
efficiency by which water displaces oil, whereas sweep efficiency is 
related to the growth portion of the reservoir which is swept and unswept 
by the injected fluid. A major cause of poor sweep efficiency is 
associated with the fact that the injected fluid generally has a lower 
viscosity than the displaced fluid (petroleum). Thus, the injected fluid 
has a higher mobility and tends to finger through the oil, prematurely 
breaking through to the production well. 
One solution to this high mobility problem is to increase the viscosity of 
the driving fluid. A way to do this is to add polymeric organic materials 
to a driving water which has the effect of increasing the viscosity of the 
water, thereby increasing the sweep efficiency of the supplemental 
recovery process. U.S. Pat. No. 3,039,529 and U.S. Pat. No. 3,282,337 
teach the use of aqueous polyacrylamide solutions to increase the 
viscosity of the injected fluid thereby promoting increased sweep 
eficiency. Polysaccharides as taught in U.S. Pat. No. 3,581,824 have been 
used for the same purpose. These polymers are quite expensive and any 
polymer lost to adsorption on the reservoir matrix adds substantially to 
the cost since additional polymer is required to maintain a given 
viscosity. 
The above described problems have been recognized by those skilled in the 
art of oil recovery and certain sacrificial compounds have been added to 
pretreat the formation in order to decrease the adsorption of subsequently 
injected surfactants and/or polymers. For example, U.S. Pat. No. 3,414,054 
discloses the use of aqueous solutions of pyridine; U.S. Pat. No. 
3,469,630 discloses the use of sodium carbonate and inorganic 
polyphosphates, and U.S. Pat. No. 3,437,141 discloses the use of soluble 
carbonates, inorganic polyphosphates and sodium borate in combination with 
saline solution of a surfactant having both a high and a low molecular 
weight component. These materials have not been completely satisfactory 
from a standpoint of performance and economics however. 
SUMMARY OF THE INVENTION 
The invention is a process of producing petroleum from subterranean 
formations having an injection well and a production well in communication 
therewith. The process comprises injecting into the formation via the 
injection well an aqueous solution of tannin either as a preflush and/or 
in admixture with a chemical oil recovery agent, for example, surfactant, 
polymer and/or a micellar dispersion. It is the usual practice to then 
inject a fluid such as water to sweep the chemical components through the 
reservoir to the production well, thereby displacing oil from the 
subterranean formation to the surface of the earth. 
DESCRIPTION OF THE PREFERRED EMBODIMENTS 
A sacrificial material is injected by the process of this invention through 
an injection means comprising one or more injection wells into a 
subterranean petroleum-containing formation to preferably occupy or cover 
all potential adsorption sites of the rock within the subterranean 
formation thereby reducing the extent of adsorption of the more expensive 
chemical oil recovery agent injected therewith. A sacrificial agent 
performs best when it exhibits high adsorption on active sites of rock 
surfaces, and thus diminishes surfactant and/or polymer adsorption. 
Chemical compounds of polyelectrolytic nature have the proper physico 
chemical and structural requirements to behave as successful sacrificial 
agents. The functional groups on the sacrificial agent molecules enhance 
adsorption either by hydrogen bonding or electrostatic attraction to 
active sites on the rock surfaces. 
A satisfactory sacrificial material has at least three important 
characteristics. First, it should be less expensive than the surfactant on 
a cost effectiveness basis since it is to be sacrificed or adsorbed by the 
formation, probably not to be recovered. Next, it must be adsorbed readily 
by the subterranean formation matrix. Preferably the sacrificial material 
should be adsorbed more readily than the chemical oil recovery agent to be 
used in the process. The third important characteristic of a sacrificial 
agent is that the presence of such adsorbed sacrificial material should 
retard or eliminate adsorption of the surfactant and/or polymer chemical 
recovery material on the adsorption sites of the formation rock. By 
adsorption sites of the formation rock it is meant those parts of the 
surfaces of the pores of the formation rock capable of adsorbing a 
chemical compound from a solution on contact. 
The sacrificial material may not have a detrimental effect on the recovery 
efficiency of the chemical flooding operation. Additional oil is usually 
recovered only if the sacrificial material is followed by or is admixed 
with a surfactant and/or a polymer chemical recovery agent which will 
effectively increase the amount of oil displaced from the subterranean 
formation. When the surfactant is chosen as the chemical recovery agent it 
should be injected in admixture with the sacrificial agent for best 
results and ahead of the following flooding water thereby achieving the 
desired interfacial tension reduction between the injected fluid and the 
displaced fluid with minimal loss of surfactant on the formation matrix. 
The surfactant may be present in a hydrocarbon solvent or in an aqueous 
solution or in a combination thereof. Any anionic, nonionic and/or 
cationic type of surfactant known in the art may be used in the practice 
of this invention. Some types of surfactants were mentioned previously. In 
addition, surfactants disclosed and claimed in the following U.S. patents, 
for example, are particularly useful since they have been found to be 
capable of performing in reservoirs having both high salinities and high 
hardness levels: U.S. Pat. Nos. 3,858,656; 3,811,505; 3,811,504 and 
3,811,507. 
Likewise, the amount of surfactant which must be employed in the practice 
of any chemical flood is generally known in the art and is to be found in 
published literature. However, the slug size of surfactant generally will 
range from about 0.01 to 1 pore volumes of an aqueous surfactant solution 
having dissolved therein from about 0.1 to about 10.0 percent by weight of 
the surfactant itself. 
In my invention the sacrificial agent may be injected ahead of or in 
admixture with the surfactant slug into the petroleum formation. A 
surfactant/sacrificial agent mixture may also be preceded by a slug of 
sacrificial material in aqueous solution. 
In any of these embodiments and others which are obvious to those skilled 
in the art, the surfactant containing slug may be followed by a material 
to taper the viscosity before drive water is injected. This technique 
known well to those skilled in the art prevents the water from fingering 
into the more viscous surfactant containing slug. 
Natural vegetable tannins are obtained from trees, leaves, wood, fruits and 
roots. The tannins are water-soluble, complex organic compounds. All 
tannin extracts contain mixtures of polyphenolic substances, and some have 
associated with them certain sugars. Synthetic tanning materials (syntans) 
are manufactured materials that are used as partial or complete 
replacements for natural vegetable tanning extracts. Most syntans are 
condensation products of formaldehyde and naphthalene sulfonic acids, 
various phenols and sulfonated phenols, diaryl sulfones, urea, melamine 
and diamide. Some syntans are produced by combining polyphenolic materials 
with lignosulfonates. The most common of these materials employs a 
formaldehyde or a furfural condensation product of resorcinol as the 
phenolic syntan. 
Vegetable Tanning Materials 
As mentioned, natural vegetable tannin materials are widely distributed in 
nature. Major sources of tannin materials are: quebracho, chestnut wood, 
wattle bark and hemlock bark. 
The actual chemistry of vegetable tannin materials is not well understood 
and therefore, naturally occuring tannins are often referred to as 
vegetable tanning extracts. There are two main classes of natural 
vegetable tanning extracts: (1) hydrolyzable extracts and (2) condensed 
tanning extracts. 
Hydrolyzable Extracts 
These materials are divided into two main groups, gallic acid and ellagic 
acid. The chemical formulas for these materials are given below: 
##STR1## 
These materials and combinations of these types of materials are 
representative of the hydrolyzable tannin extracts found in nature. 
Condensed Tanning Extracts 
Condensed tanning extracts are found principally in the roots, bark and 
wood of plants. For example, in the quebracho and wattle trees. The 
following structure is assumed by most of those skilled in the art to be 
the principal structural skeleton of this type of tannin molecule. It is 
called the flavan structure. 
##STR2## 
Synthetic Tanning Materials 
The principal syntans are condensation products of formaldehyde and various 
other materials including naphthalenesulfonic acids, various phenols and 
sulfonated phenols, diaryl sulfones, urea, melamine, and dicyandiamide. 
Other syntans are produced without formaldehyde using materials such as 
lignosulfonates. The two most common categories of syntans are 
naphthalenic syntans and aromatic hydroxy syntans. The principal 
structures of these two types of materials are given below. 
##STR3## 
Aromatic hydroxy syntans may be made by two general methods. The first 
method sulfonates an aromatic hydroxy compound and then condenses this 
product with formaldehyde. The second method condenses an aromatic hydroxy 
compound with formaldehyde and then sulfonates the resulting product until 
it is water soluble. Aromatic hydroxy syntans may be made into less 
expensive materials by combining then with lignin sulfonates. 
A complete discussion of synthetic and natural tannin materials may be 
found in Kirk-Othmer Encyclopedia of Chemical Technology, 2d Edition, 
under the subject heading, Leather. 
Tannins may be chemically modified to obtain products with improved 
properties, such as higher tolerance to salinity and hardness and 
increased adsorption to rock surfaces. Several modification reactions 
employed are sulfomethylation, carboxylation, oxidation, ethoxylation and 
formaldehyde condensation. 
Commercially available syntans are sold under the tradenames Lomar D, Lomar 
LS, Lomar PW, Blancol, Monotan R, Nopcotan A-6-S-D, Neradol D, Neradol N, 
Leukanol and others. 
Tannins (natural vegetable tannins or synthetic tanning materials) are 
suggested to be utilized as a preflush slug followed by a surfactant slug, 
in order to adsorb on rock surfaces and satisfy the adsorption sites and 
thus minimize surfactant adsorption. It is also suggested to use these 
tannins as sacrificial agents in admixture with surfactant systems. In 
certain applications admixtures of sacrificial agents and surfactant 
systems prove to be more effective in improving oil recovery. Following 
the injection of the surfactant system, with or without sacrificial agent, 
the suitable drive fluid (e.g. water, higher viscosity water--thickened 
with polymers) may contain tannins which will aid in the desorption of 
surfactant, by adsorbing on those sites previously occupied by the 
surfactant molecules. This will increase surfactant concentration in the 
flood water, and thus contribute to displacing additional oil. If 
polymeric solutions are used as a portion of the drive fluid, the 
sacrificial agent (tannin) will in turn decrease the adsorption of the 
polymer on the rock matrix. This will have a beneficial effect in 
maintaining the proper mobility ratio between the surfactant slug and 
displaced fluid, and thus achieve high sweep efficiency and vertical 
conformance. The combination of extended displacement efficiency and sweep 
efficiency contributes to high oil recovery in enhanced oil recovery 
processes. 
The quantity of tannin to be injected into the subterranean hydrocarbon 
formation may be any amount up to and including an amount sufficient to 
occupy substantially all of the active sites of the formation matrix. If 
less than the maximum amount is used, there will be a corresponding 
increase in the adsorption of surfactant from injection solution onto the 
formation matrix although the amount of increase will not be as great as 
in the case where the formation is completely free of tannin. At a 
maximum, only the amount of tannin needed to completely occupy the active 
sites on the formation matrix is needed. To be effective, the amount used 
should reduce the adsorption of surfactant on the reservoir matrix. The 
detriment resulting from using excess tannin would be an increase in the 
cost of operating the oil recovery program. 
The amount of tannin needed in the process of the invention depends on the 
particular formation, the area of pattern to be swept and other formation 
characteristics. Those skilled in the art can determine the exact quantity 
needed to afford the desired amount of protection. 
Generally it has been found that the amount of tannin will be effective in 
amounts of from 0.01 to 1.0 pore volumes of the aqueous solution of 
surfactant-sacrificial agent or only sacrificial agent solution.

The effectiveness of this invention for reducing the adsorption of 
surfactant or polymer on the formation rock and chemical flooding 
operations is demonstrated by the following examples which are presented 
by way of illustration and are not intended as limiting the spirit and 
scope of the invention as defined in the claims. 
EXAMPLE I 
The performance of tannins as sacrificial agents was evaluated by testing 
LOMAR LS* in a surfactant flood and determining its effect on the tertiary 
oil recovery efficiency of the surfactant system. Surfactant floods were 
performed using the surfactant-solubilizer system: 0.54% TRS 18+1.22% TRS 
40+0.74% Adduct N-60 CS**. A base run was performed by surfactant flooding 
a waterflooded limestone core at 109.degree. F. which was initially 
saturated with Slaughter formation water and Slaughter crude oil. An 
amount of 0.4 PV of 2.5% surfactant solution prepared in Slaughter 
formation water was injected, and then was followed by 1000 ppm Xanflood 
(polysaccharide) polymer solution prepared in fresh water. The oil 
recovery efficiency of the base run was 58.9%. A similar surfactant flood 
was performed in the same core after the core was cleaned and resaturated 
with Slaughter formation water and crude oil. The flooding conditions were 
kept exactly the same as those for the base run, except for the fact that 
2% Lomar LS was incorporated into the surfactant system. An amount of 0.4 
PV of 2.5% (TRS 18/40-Adduct N-60 CS) +2% Lomar LS prepared in Slaughter 
formation water was injected, and then was followed by 1000 ppm Xanflood 
polymer solution prepared in fresh water. The oil recovery efficiency of 
the second run was 84.6%. 
FNT *Lomar LS is believed to have a structure similar to: 
##STR4## 
FNT **TRS-18:petroleum sulfonate, TRS-40:petroleum sulfonate, Adduct 
N-60CS:chain sulfonated 6 mole ethylene oxide adduct of nonyl phenol. 
In the core floods performed, Lomar LS substantially increased the tertiary 
oil recovery efficiency (from 58.9% to 84.6%) of the petroleum 
sulfonate-solubilizer surfactant system employed. It is, thus, concluded 
that tanning materials can be effectively used as sacrificial agents in 
surfactant floods. 
EXAMPLE II 
Lomar D, Lomar PW, Lomar LS, Lomar ST and others are synthetic tanning 
agents (manufactured by Diamond Shamrock) which have high salinity and 
hard water tolerance, and exhibit no adverse interaction with surfactant. 
These polyelectrolytes have chemical structures which make them suitable 
candidates for sacrificial agents on carbonate surfaces. Both Lomar PW 
(Na.sub.2 SO.sub.4 :6%) and Lomar LS (Na.sub.2 SO.sub.4 :1%) were tested 
to determine their effect on adsorption of petroleum sulfonate-solubilizer 
system (TRS 18/40-Adduct N 60 CS) on Slaughter (carbonate) core material. 
77 Kg/m.sup.3 (7.7%, w/v) TDS brine was used. Slaughter core material was 
crushed, cleaned and sieved. The fraction that passed a 200 mesh size 
sieve was used as adsorbent in adsorption tests. Shake bottle tests were 
conducted by contacting 20 g of crushed Slaughter core material with 50 cc 
surfactant solution for 24 hours at 43.degree. C. (109.degree. F.). 
Adsorption values of 2.5% (1%) Slaughter 2 surfactant system with/without 
sacrificial agent present are tabulated below: 
______________________________________ 
mg Surfactant Adsorbed 
Sacrificial Agent 
g Crushed Slaughter 
Core Material 
______________________________________ 
No sacrificial agent 
2.9 (2.8) 
0.5% Lomar PW 
0.22 (0.3) 
1.0% Lomar PW 
0.15 (0.05) 
2.0% Lomar PW 
0.1 
0.5% Lomar LS 
0.6 
1.0% Lomar LS 
0.25 
2.0% Lomar LS 
0.2 
______________________________________ 
Results indicate that both Lomar PW and Lomar LS are very effective in 
reducing surfactant adsorption on crushed Slaughter core material.