A PROCESS FOR REDUCING THE VISCOSITY OF HEAVY OIL. By E. A. STARKE.1

The oils of the Casmalia section of the Santa Maria field are of an exceptionally viscous and sticky nature. Their gravity ranges from some 8 to 16° B. With an average gravity of some 10° B. combined with high viscosity, it is impossible to commercially transport them by such means as pipe lines without subjecting them first to a preliminary treatment to raise their gravity and lower the viscosity.

It is only during the past few years that the importance of the heavy oils has been realized and their intensive exploitation carried on. Formerly these heavy oils had a limited use as road building materials, and in the manufacture of asphalt. As soon, however, as the refiners of light petroleum products placed the residuum from their refining operations on the market for the same purposes the demand for heavy petroleum fell off. In view of this, the heavy oil fields, such as those existing in Santa Barbara County, were neglected. Renewed interest, however, was taken in these fields when the demand for fuel oil rose to the figures we are witnessing today.

In order to be commercially useful, as a fuel, these heavy oils must be capable of transport through pipe lines without the application of heat, and, furthermore, their use must not be restricted to apparatus having specialized heating arrangements.

For the extensive fuel utilization of the Casmalia crude, a certain preliminary treatment is necessary in order to bring it up to the required standard. This treatment has heretofore consisted of heating the oil to a temperature of 180° F. and mixing therewith light distillate in a special type of mixer. In this way a high quality product is obtained which can be transported through a pipe line, and which meets the full market demands.

A number of objections arise against the above mode of treating the heavy crude, chief of which are the high cost and scarcity of light distillate, and secondly the fact that production of the mixed product is dependent on the supply of light distillates obtainable. A third important objection rests on the ground that full value is not obtained from the crude oil in this manner. For these reasons other methods of treating the crude were found imperative, with the result that the DohenyPacific Company adopted, at its Casmalia property, a process patented by the writer in 1905, and which had already been proved commercially successful.

The Starke process is based on the principle that when a heavy asphaltic oil or residuum is heated to 700° F. the crude oil suffers dissociation or cracking, particularly that part of the crude which renders

We are enabled to publish this article through the courtesy of E. A. Starke, Chemical Engineer, Berkeley, California,

it sticky and viscous. In order that the process can be carried out successfully it is necessary that the oil be dry, as water interferes with the cracking operation. Not only does this method reduce viscosity, but a certain percentage of synthetic gasoline is formed. If it is desired to obtain a large percentage of this cracked gasoline, it is necessary to employ pressure. However, even when the prime object is to reduce viscosity, from 3-6 per cent of synthetic gasoline is formed during the operation. It is advisable in all events to so employ the process that the largest amount of synthetic gasoline under the given conditions is obtainable. In this way the operating costs are lowered.

In a general way the process as it is practically carried out consists in pumping 100 barrels of dry oil into a 125 barrel still. Approximately 40 barrels of oil is now distilled off. The heat under the stills is then discontinued, and the distillate is reunited with the residuum contained in the still. This may be done either by first cooling the still and adding the distillate, or by mixing the distillate and residuum without preliminary cooling. The last method is the one generally adopted. In this way the cold distillate is thoroughly mixed with the heavy asphalt still bottom, at the same time cooling the mixture sufficiently so that the charge can be withdrawn. The resulting product has now a gravity of between 11-12° B. and the viscosity is about equal to that of a 16° B. Kern River crude. The heat units per barrel are equal to those of the Kern River crude, about 18.800 B.t.u. but being of a lower gravity. A barrel of this processed oil will produce more steam than a barrel of the Kern crude or residuum. The viscosity of the oil produced will necessarily be dependent on the amount of distillate taken from the crude and then reunited. If, however, more than 50 per cent of the crude is removed during the distillation process, a certain amount of carbon is formed which would be classed as an impurity. Actually this carbon is so finely divided that it does not interfere with the uses of the oil.

During the distillation from three to five per cent of the oil is given. off as a gas which contains much of the sulphur present in the well. This gas is burned under the stills as fuel. Considered in detail, the plant as operated on the Doheny property presents the following features:

A continuous distillation system utilizing a battery of four stills working as a unit. These stills are of 600 barrel capacity and are provided with the necessary preheaters, condensers and other distilling accessories. Comparatively dry oil is pumped through a heat exchanger into still number one. Here the temperature of the oil is raised to that point at which the most volatile fractions are given off. The oil then passes from the bottom of this still into the center and back section of still number two, maintained at a higher temperature than still number

one.

Here a second fraction is is given off, and passed into the condenser. From still number two the oil flows into the center of still number three, maintained at a higher temperature than the preceding two. Here a third portion of the volatile constituents contained in the oil are given off. From the third still the oil flows into a fourth one. Here the oil attains a temperature of about 750° F. and the remaining fractions distill off.

The residuum of still number four is now passed through the inner tubes of the heat exchanger before mentioned, where it loses a part of its heat to the incoming crude. From the heat exchanger the residuum flows into a sort of churn where it is mixed with the distillate portions recovered from the various stills. The resulting mixture is now limpid and can be pumped and used in the same manner as the 16° B. Kern River oil, and is equal in quality to the best crude used for fuel purposes. In conclusion it may be stated that with the increasing use of synthetic gasoline as a source of motive power, the heavy petroleum oils assume an important role from an economic standpoint, and such methods as the one described, by which both high grade crude fuel oil and synthetic gasoline are obtained, merit the attention of the oil producer.

CHAPTER II.

COMPARISON OF VARIOUS METHODS OF EXCLUDING WATER FROM OIL WELLS IN CALIFORNIA.

(As shown by results of test for water shut-off)

By R. E. COLLOM, Chief Deputy.

All of the mechanical operations at a drilling well which aim at the protection of productive oil or gas bearing formations from infiltrating waters, and also certain geologic features, contribute data for determining the result of the test for water shut-off. These data include:

(1) Total depth of hole and depth to which hole is bridged to land water string.

(2) The method of drilling: Rotary or Cable.

(3) The diameter, weight and length of casing used as water string. (4) The method of making water shut-off.

(5) Such natural features as stratigraphic position, chemical composition and hydraulic head, or fluid-level, of water or waters excluded.

(6) Record of all other formations entered, both above and below the depth of shut-off, including oil, gas and water.

In this paper the various items specified above are discussed only as they apply to operations for shutting of top or intermediate waters in the oil fields of California.

Definition of Terms.

Water shut-off: The term water shut-off is commonly applied, in California, to the condition whereby waters, native to strata penetrated in drilling, are excluded from the well and prevented from moving below a given depth, by landing or cementing a string of easing at that depth.

Top water: The term top water is applied to waters overlying the shallowest productive oil zone in any given area.

Intermediate water: The term intermediate water is applied to waters native to strata lying between any productive oil zones.

Water string: A water string is a string of casing which is used to exclude water from an oil well.

Source of Data.

The official reports on test of water shut-off of the Department of

"There are two kinds of reports issued to operators: (1) Reports on Test of water shut-off; and (2) Reports on Proposed Operations. The reports all bear serial numbers showing the kind of report, the district from which the report originates, and the individual number of each report. Thus, Report No. T 1-24 is Report No. 24. on test of water shut-off, originating in District No. 1. Likewise, Report No. P 3-56 is Report No. 56, on proposed operations, originating in District No. 3. Each of these reports bears a decision or recommendation, either relative to a test or to certain proposed work. The decisions of the respective districts are summarized for the Annual Report. and appear under the subject "Decisions," in the chapters covering work done in each district during the fiscal year.

Petroleum and Gas, issued from the various field offices during the fiscal year closing June 30, 1918, are the principal source of the data in items 1 to 5, inclusive, referred to above. They are taken from 890 reports on test for water shut-off. They are tabulated by districts, fields, and sectional or lease locations in Tables I, II, III, IV and V. These tables are printed on pages 148 to 195. The respective results of test and supporting remarks are also given in the tabulations. Complete data were not available in all instances.

With few exceptions, only those reports on shut-offs made in the process of new work or deepening operations are considered in this discussion. This excludes numerous tests of the efficacy of plugs for shutting off water below productive formations-so-called "Bottom water”—or plugs in abandonment jobs, or tests of strings set with packer in redrilling jobs. These are more properly remedial operations and, therefore, are aside from the purpose of this discussion.

Tests.

The usual pumping or bailing test for water shut-off is made to determine one specific question, namely, whether or not water is prevented from passing around the shoe of the water-string and into the well. It is well worth noting that when a pumping or production test is made, a positive answer can be given only if the production shows no water. If water is present, it is evident that the source of the water can not be determined by the mere act of pumping the well. In such cases it therefore becomes necessary to bridge or plug under the water string, or perform other operations, in order to determine the source of the water. Pumping or production tests, although apparently expedient for quickly getting the well on the producing list, should be avoided where it is possible to do so. It becomes increasingly difficult and distasteful to perform the necessary testing and corrective operations as the well is deepened through formations below the shoe of the water string. The time to determine whether or not a string of casing shuts off water is when the minimum number of complications can enter into the results. Such possible complications will be discussed later under Factors in Results of Tests.

The following are the necessary steps in a bailing test1:

(1) Bail the well to bottom or to a predetermined fluid level. The correct depth to bail a hole depends upon (a) the fluid level of water back of the casing, (b) the strength of casing to resist collapse, (c) the nature of formations and condition of the hole at or shortly below the shoe of the casing.

(2) The well should stand undisturbed for at least twelve hours. Neither bailer, tools nor casing should be run in the hole during this time.

'Method of testing Water Shut-off at Oil Wells. Second Annual Report, Bull. 82, Cal. State Mining Bur. pp. 57-58.