February 2 0 , 1933
INDUSTRIAL
A N D ENGINEERING
CHEMISTRY
51
The Dowell Process to Increase Oil Production SHERMAN PUTNAM, Midland, Mich.
I N THE PROGRESS OF CIVILIZATION, it seems that one can usu-
ally analyze the various steps of any development somewhat as follows: First, a commodity is produced by main strength and awkwardness; then it is produced by rule-of-thumb method, and, after i t is produced by this method long enough, it is generally said that the commodity is produced scientifically. However, a later stage of production seems to be the chemical stage, in which the rule-of-thumb methods are interpreted or corrected according t o chemical reaction. The oil industry is no exception to this rule. For example, the haphazard rule-of-thumb drilling practice over a period of time has been replaced by highly developed equipment, operated with technical supervision and control. Oil-well operation has been systematized b y the application of engineering principles to the point where operators now work according to definite schedules of maintenance and production. Physical and chemical sciences are also being applied to oil-production methods with results that have aroused the interest of all oil producers. During t h e past few months a new process has been put into commercial use by The D o w Chemical Co. through its subsidiary, Dowell, Inc., whereby the oil production, if it comes from a calcareous formation, can be apprecably increased by the proper type of an acid treatment. The use of acids in wells is not a new idea; as a matter of fact, a patent taken out by Frasch (U. S. Patent 556,669, issued March 17, 1896) specified the use of hydrochloric acid on limestone formation. On the other hand, the control and technic of directing the acid in a well so that it will work upon the oilproducing formation rather than become a destructive force was not discovered until the Dowell process was perfected. The history of this development is somewhat interesting. HISTORY OF DOWELL PROCESS
In 1929 a demand for increased production of natural brine in the plant of T h e Dow Chemical Co. led to the thought of attempting to open up the crevices of the producing rock by some method other than the use of nitroglycerin. The brine was produced, for the most part, from a very high silica content sandstone, although this rock does contain a certain percentage of calcareous material. Acid was· used by two different methods. In t h e first place, it was fed into the well along with a stream of brine for diluting purposes, feeding the brine and acid mixture back into the producing formation. A certain absorption was possible, using various pressures on the feed, and an interesting curve was plotted showing the increase of absorption of the acid brine with an increase of fluid pressure until a certain maximum pressure was reached where the leveling-off of the curve took place and almost any volume of brine could be absorbed back into the strata. T h e work was of interest, but only in an experimental way. The acid could not be fed in as a raw acid, as the pores of the producing formation were so minute that the small amount of iron and manganese precipitates was detrimental to the improvement in production. It was therefore necessary to filter very carefully before addition, as well as inhibit very carefully and properly the acid so as not to bring about detrimental corrosion in the iron system of the well. T h e second state of development was practically the reverse of the first. Instead of feeding brine in with the acid, a charge of acid was fed directly into the well, and a certain head of brine or oil was pumped in on top. A t first the difference in head of the two fluids was relied upon to bring about sufficient pressure to feed the acid back into the rock, and later by the application of mechanical pressure this was more completely accomplished. Positive results were accordingly secured. T h e lack of a large percentage of calcareous rock in or adjacent to the brine formation prevented the treatment from showing very great promise for improved production. However, in a well which had previously been discarded as a nonprofitable producer, it was possible t o increase its production some 25 per cent, thereby making the well a paying investment. During these experiments on the brine-producing sand formation, neighboring oil-well owners became interested, and as a result of the combined efforts of The D o w Chemical Co. and The Pure Oil C o . , oil production was increased. The patents relating to this procedure taken out by both companies were assigned to Dowell, Inc. The oil, however, was produced from a limestone formation at a much greater depth than the brine. The results obtained were interesting, if not phenomenal, from the start. However, the apparent possibility of making an error of a few feet one way or another in depth when working at a distance of o-ver a half-mile, immediately suggested the possibilities
of chemical action taking place where it might do harm rather than good. In many wells the casing used to close off the upper water formations from the oil-producing sand is embedded in a limestone formation and apparently is sealed at this point. However there is a possibility of the acid attacking the seat of the casing in the limestone formation as much as there is a possibility of its attacking the limestone which produces the oi—therefore, the need of very careful analysis and expert control in the treatment of a valuable oil well. Difficulties due to water, unspent acid, plugs, and paraffin were also encountered. To begin with, the method of inhibiting the acid had to be improved. The original system used on brine wells in 1929 was not sufficiently fool-proof to make it a satisfactory product to use in continuous treatment. A new type of inhibitor was developed, one having real lasting qualities, making it possible to ship the acid for treatment in iron tank cars and further making it possible to use this same acid through ordinary pumping equipment for the development of pressures required for the treatment. In a further development of the technic, a method of arriving at an accurate determination of exactly where the acid is when the treatment starts practically insured the safety of the casing seat. As the process developed, a need for paraffin removal became more apparent and various factors involved in the development of the process made it possible to consider a new method of attack on this old problem. Two types of paraffin solvents are now included in the Dowell service: one a solvent of heavy gravity satisfactory for removing the waxes below a layer of water; another a solvent of a lighter gravity, making it possible to remove the waxes from the well and tubing. The uses of mechanical means, as well as chemical, for the proper saturation of these solvents and the removal of the dissolved waxes by pumping them out of the well with production have all assisted in making this new well service one of tremendous benefit and value to the oil industry. From the chemical engineer's standpoint, it is believed that the success of the Dowell process can be credited to the application of chemical engineering principles to oil production. DESCRIPTION OF THE PROCESS
To elaborate more fully upon the method of procedure, it might be interesting to read the description of the process as published in U. S. Patent 1,877,504. The present invention relates to the treatment of deep wells, such as oil, gas, brine or water wells, to increase the output therefrom. I t is more especially concerned with the treatment of wells in which the mineral-bearing stratum consists of a limestone or other calcareous formation, or is contiguous to such a formation. An object of the invention is to counteract some preventable natural causes for the decline of yield of a well. A familiar example is the decline of production of an oil well. When it is first drilled into an oil-bearing stratum, the release of pressure upon the oil deposit may cause the well to flow naturally for a certain length of time. The flow will gradually recede from the initial high point to the point where natural flow does not produce a sufficient yield, and thereafter pumping will be resorted to, until the continued decline in output renders further operation unprofitable. In many cases, however, the stoppage of oil output is caused, not by exhaustion of the oil supply, but by the building u p of solid deposits of wax or t h e like in t h e channels and pores of t h e oil-bearing rock which obstruct and finally may cut off altogether the flow of oil to t h e well. Various methods have been used for opening up or cleaning a clogged well hole, such as drilling, "shooting" with explosive or by chemical treatment. The first two methods mentioned have t h e disadvantage t h a t the pump rod and tube must be removed prior to applying the treatment, in addition to which, in the case of using an explosive, there is danger of damaging the casing. T h e chemical methods heretofore proposed have either not been found effective to clear t h e hole or they have involved the use of corrosive substances which are injurious to the metal parts of the well structure. As an illustration, a chemical method is described in United States Patent 556,669, according to which the flow of an oil well in a limestone formation is increased b y treating with a quantity of an acid, such as hydrochloric acid. The acid has the effect of attacking and dissolving the rock, thereby enlarging the cavity a t the bottom of the well, or the channels and pores in t h e rock through which oil flows to t h e well. In actual practice, however, this method h a s never been generally adopted, due to t h e fact that the acid attacks the metallic casing, pump tube, etc., about as actively as t h e rock, and causes serious damage thereto. We have now found t h a t the last-mentioned method may be adapted for use in increasing or restoring t h e flow of oil wells by suitable modification without material injury t o the casing or other metallic parts of the well. The treatment can be carried out at less cost a n d with better results than any of t h e methods heretofore employed. The invention, then, consists of
52
NEWS
the improved method hereinafter fully described and particularly pointed out in the claims. In carrying out our improved method we employ a mineral acid, preferably hydrochloric acid, inasmuch as the latter upon reacting with the calcareous rock forms water-soluble salts which remain in solution and are removed from the well with the spent acid. To the acid we add a small amount of a sub stance capable of inhibiting attack of the acid upon metal surfaces—e. g., of iron or steel, copper, etc.—with which it comes in contact. As the inhibiting agent we prefer to use an arsenic compound soluble in the acid solution, examples of which are arsenic acid, H3ASO4, arsenic trioxide, AS2O3, or a solu ble arsenate or arsenite, such as the corresponding alkali metal salts. The amount of arsenic compound added may be varied, but we have found that from 1 to 5 per cent thereof, based upon the weight of the solution, will be satisfactory for the purpose. Other inhibitors which may be used are cyanides, organic nitrogen bases, such as aniline, phenyl-hydrazine, pyridine, quinoline, acridine, and derivatives thereof, organic sulfur compounds, such as mercaptans, as well as various by-products of industrial processes, such as sludge acid from oil refining and residues from acid sulfite paper manufac ture, etc. The strength of the aqueous hydrochloric acid solution, in general best adapted to the purpose in hand, may be between about 5 per cent and about 20 per cent, and preferably should be between 10 and 15 per cent, although other concentrations may be used, if desired. With such strength of acid the corrosive action thereof upon metals, particularly iron or steel, can be largely or substantially inhibited by adding thereto a relatively small amount of an arsenic compound or other inhibiting agent. Consequently, the acid can be introduced into the well through the pump tube, so that the latter need not be withdrawn prior to the treatment. It is sufficient merely to pull the pump rod and valves, and to pour the acid solution into the well through the tube. Due to the presence of the inhibitor there will be no sub stantial attack upon the pump tube, or upon the well casing if the charge of acid rises high enough in the well to contact with the casing. The acid solution is preferably added in amount calculated to fill the bore of the well to a depth not exceeding the thickness of the mineral-bearing stratum. In order to force the charge of acid out of the pump tube into the bore of the well against the head of oil standing in the hole, it may be fol lowed by a charge of oil, water, or other liquid sufficient to overcome the head, or pressure may be applied by other suitable means—e. g., by air pres sure or by means of a pump. When introduced into the bottom of the well, the acid attacks the rock structure and dissolves or disintegrates it, thereby enlarging the pores and channels in the rock, or opening up new channels. The action of the acid upon a limestone formation causes the evolution of a considerable volume of carbon dioxide gas. This gas may be allowed to escape up the casing, or the latter may be capped off, thereby creating a gas pressure within the well which assists in forcing the acid into the pores and crevices of the rock. After the action of the acid has practically ceased, the spent solution containing the dissolved salts may be pumped or bailed out. In many cases it may be desirable to repeat the treatment one or more times. By making successive additions of smaller amounts of acid solution, and pumping out the spent acid between charges, a greater cumulative effect may be produced than by the use of a single larger charge. It is not necessary, however, to add the acid solution through the pump tube, as any other convenient way may be employed. For instance, the pump tube may be withdrawn and a dump bailer used to lower a charge of acid into the base of the bore. In the practical use of our method in the central Michigan oil field, where the oil is derived from a calcareous rock formation, we have successfully used hydrochloric acid solutions of 10 and 15 per cent strength to which was added a small amount—e. g., 1 to 5 per cent—of an arsenic compound. For example, to 4500 pounds of a 15 per cent hydrochloric acid solution were added 2 gallons of arsenic acid solution containing 21 pounds of arsenic calculated as As2O6. The mixed solution was charged into an oil well through the iron pump tube, being followed by a quantity of crude oil t o force the acid solution out of the tube into the well. After the acid was exhausted, it was pumped out, and thereupon regular pumping of the oil was resumed. The production of the well was approximately doubled with one treatment. The method has been used repeatedly for the treatment of low yield or exhausted oil wells in producing territory with a resultant increase of output amounting to as much as 75 to 200 per cent, and in some cases wells which have ceased to flow have been brought back with a resumption of natural flow. The treatment has been applied in the manner described without ap preciable damage to the pump tube or well casing. The invention may also be employed similarly to increase the flow of gas wells and brine or water wells in cases where the mineral or water-bearing stratum, or the imme diately adjacent strata, are of a limestone or calcareous formation, or of a nature such as to be acted upon and dissolved by hydrochloric acid solution. Other modes of applying the principle of our invention may be employed instead of the one explained, change being made as regards the method herein disclosed, provided the step or steps stated by any of the following claims or the equivalent of such stated step or steps be employed. ADDITIONAL PATENTS FILED Additional patent applications are on file and it is expected that Dowell, Inc., will, before many months, have a number of patents to its credit covering many unique and economic processes for the improvement of oil-well production. It is hardly neces sary to say that the oil industry looks upon these developments as rather revolutionary factors in oil production. The applica tion of the principles are not limited to the oil industry alone, as natural gas production has already received the benefit of many Dowell treatments.
E D I T I O N
Vol. 1 1 , No. 4 THE
I N ITS PHOPOSED B Y - L A W S the Pitts burgh Section, un d e r Section 11, has e s t a b l i s h e d the Pittsburgh Award, t o s y m b o l i z e the h o n o r and apprecia t i o n a c c o r d e d to t h o s e w h o have rendered distin guished service to chemistry in that community. A Committee on De s i g n was appointed, cοnsis ting of A l e x a n d e r Silver an, chairman, L. H . Cretcher, and J. D . Edwards. The committee, in c o operation, with the Associated Artists of P i t t s b u r g h , offered a prize of o n e hundred dollars for the best medal d e s i g n submitted. T h i r t e e n models were s u b m i t t e d , a n d of those the one b y Frederick Fisher Florig, d e s i g n e r , a n d M rs. Lois Whitcomb Rhead, s c u l p t o r , shown he rewith , was chοsen. No one h a s yet b e e n chosen t o receive the first medal award.
PITTSBURGH AWARD
THE PIITSBCROH AWARD TO
Fou OUTSTANDING SERVICE TO CHEMISTRY AMERICAN CHEMICAL SOCIETY PITTSBURGH SECTION
D E L A W A R E SECTION H O N O R S P R E S I D E N T - E L E C T
REESE
O N THE EVENING of February 15 the Delaware Section held a dinner in honor of Charles L. Reese, President-Elect of t h e SOCIETY. More than fifty were in attendance. E. C. Bertolet w a s present to extend the greetings of the Philadelphia Section, of which Doctor Reese was chairman at the time the Delaware Section w a s formed, later serving in the same capacity for the Delaware group. Roger Adams, University of Illinois, and a Director of the SOCIETY, spoke interestingly of some of the uni versity problems under present conditions. C. M. A. Stine served a s toastmaster and in presenting Doctor Reese gave a brief biographical sketch, with special reference to his academic a n d industrial contributions. Doctor Reese spoke in a v e r y pleasant vein, giving some of his early experiences, as when chief chemist of the New Jersey Zinc Co. where he was intimately connected with the early days of the contact process for sulfuric a c i d . H e also referred t o what may be regarded as his greatest success—namely, the choice of men, many of whom have risen t o places of great responsibility in the du Pont organization. Following the dinner the regular meeting of the section w a s h e l d , Arno Viehoever of the Philadelphia College of Pharmacy a n d Science speaking on "Living Materia Medica." H e demon strated b y means of motion pictures the therapeutic action of medicinal drugs in living animals, the water flea, a completely transparent organism, serving as the test subject.
SUMMER S T U D Y I N C L E V E L A N D WESTERN RESERVE UNIVERSITY has announced a six weeks' summer session, beginning June 19 and closing J u l y 28, for teachers, supervisors, administrators, academic students, and those desiring study for professional improvement or cultural enrichment. The faculty will be composed of members of t h e regular university faculty, visiting professors being invited for courses in special fields. Public lectures by experts in their chosen specialties, plays, concerts, and social gatherings will be provided, as well as recreation in the form of tennis, golf, swim ming, a n d horseback riding. A complete bulletin of t h e courses a n d other information may be procured upon application to Western Reserve University, 10940 Euclid Ave., Cleveland, Ohio.
