dence, centered about the drilling of certain wells with rotary in the Sunset field, is entirely applicable to the present discussion:

MR. COLLOM (to Witness E. A. Whitten, driller, Union Oil Co.): I would like to ask Mr. Whitten if he believes in drilling through this top sand, where it is of a thickness of twenty feet or so, whether the returns from that well, from that sand, would show at the surface of the well, even if the sand were present. A. Oh, yes.

MR. COLLOM: You believe it would be possible to detect the presence of that sand?

A. You can not tell in your returns from your rotary, but you can tell the way the mud is pumping.

MR. COLLOM: Can you tell which ones are water sands and which ones oil sands?

A. We have encountered oil sands in spots, and by little bubbles of gas you can locate pretty closely by rotary drilling.

MR. COLLOM: What we are trying to get at in a condition of this kind is whether it would be possible to pass through it without detecting it with a rotary. We will say the drill plunged through that sand, but there would be no means of telling when the returns came to the surface that you have been passing through a water sand or an oil sand.

MR. SCHNEIDER (Commissioner): It would show some discoloration or something to show that it had some signs of life.

MR. COLLOM: As a matter of fact, it is a pretty risky matter to depend upon a rotary?

MR. SCHNEIDER: Yes, it is.

MR. MCLAUGHLIN: Let me ask the rest of the Commissioners if they are not convinced of that.

A COMMISSIONER: I think you can.

MR. MCLAUGHLIN: Mr Saine?

MR. SAINE (Commissioner): I believe you can.

MR. MCLAUGHLIN: Mr. Ballagh?

MR. BALLAGH (Commissioner): I think you can.

MR. MCLAUGHLIN: Mr. Schneider, you are the only one who agrees with me that it is risky. Oh, Mr. Williams, I forgot to ask your opinion. Mr. Williams, isn't it risky? Can you always pick out a sand and know that it exists when you are drilling with a rotary?

MR. WILLIAMS (Commissioner): It would be rather risky. If it were a good lively sand it might show up, but if it were dead it might take twenty feet without showing. It all depends on the character of the sand.

MR. MCLAUGNLIN: As I understand, what they have been trying to bring out is that there is some difficulty in locating a sand with a rotary.

MR. SAINE: I might be able to help you. In drilling with a rotary there are only certain formations that you can plunge through. Now, if he was drilling in a clay or shale and then struck an oil sand it would begin to plunge, and he would undoubtedly stop until he got the returns from that formation from the

bottom of the hole and washed it out to see whether he had any sand. He could tell, a man that is accustomed to it, could tell almost the minute his formation changed whether he was drilling in clay or shale, or a sand, or a shell.

Clay Trammell, being first duly sworn, testified as follows:
MR. JOHNSON: What company are you with?

MR. TRAMMELL: Lake View No. 2 and Interstate Oil Company.
MR. JOHNSON: And you are working as a driller for this company,
are you?

A. Yes, sir:

MR. JOHNSON: In drilling wells in the Maricopa Field, have you ever, in drilling with a rotary, known of a case where your drill ran through the top oil sand and you failed to find a sand, detect it, in drilling?

A. Yes, sir.

MR. JOHNSON: What well was that, Mr. Trammell?

A. Well No. 20. Interstate. We drilled by the sand, or I did myself, and at that time I recorded it as being a soft formation, and then afterwards we circulated, well, I don't know, but we drilled on through this and afterwards went on with the rotary. But we gave it plenty of time.

MR. JOHNSON: Do you know whether on Lake View No. 2 there was a similar condition?

A. Well, I can't recall whether we actually drilled through the sand. on Lake View No. 2.

MR. JOHNSON: Is it your opinion that it is possible to pass a sand in a thickness such as in the one we have been discussing with the rotary without discovering its character?

A. You certainly can if you are not very careful.

MR. MCLAUGHLIN: By being very careful you mean every man on every tour would have to watch it all the time?

. A. Yes, sir.

MR. COLLOM: In drilling through this particular sand on Interstate No. 20, how long did you circulate until you noticed, until you were able to detect sand in the returns?

A. When a well is 2500 feet two hours or two hours and a half gives plenty of time. Before you do that, before you start in circulation, the principal thing is to clean your ditch so this will show up, wash your ditch out good, and then your returns will show exactly from where you are drilling.

MR. COLLOM: Great care would have to be exercised in order to be able to catch it, and in the case you mention it would probably take three or four hours before you got returns at the surface. A. It would take that long to find a change of the formation.

Of

course, if there was a change of formation you would know it. MR. COLLOM: Of course, in the particular well that you are speaking about, No. 20, as soon as you got within the zone of the soft sand you would know it.

A.

We have the measurements of the well correctly and I know that
I had got into something soft, and I drilled on down until I

had a change of formation; I didn't know just what it was; but I was looking for this sand at the time, but I had to go ahead until I got the change of formation.

MR. COLLOM: In this particular case, Mr. Trammell, if you had continued drilling ahead, when you struck this soft sand, is it or

is it not probable that you would have been able to detect the returns after two or three hours' drilling?

A. I hardly think so. It would be difficult if you don't look.

Most of the failures for the rotary drill in the Sunset field are listed in Table IV under Sections 4 and 5, T. 11 N., R. 23 W., S. B. B. and M. The formational conditions here are much more complex than in Coalinga. However, the persistence and regularity of the many water and oil bearing formations permit correlation of strata, in cross-sections, with considerable assurance. The major causes of failure attributed to drilling in the Coalinga field also apply here.

It is true that the proper preparation of the hole, prior to making water shut-off, has a great deal to do with the success of a job. There has been considerable speculation as to whether or not rotary mud, near the shoe, prevents a successful shut-off. If the mud fluid near the shoe is completely displaced with cement, all other conditions being favorable, the job would be a success. However, the results of cementing operations, which will be discussed later, undoubtedly throw the burden of proof upon this phase of rotary drilling, rather than upon the method of cementing.

In order to make successful shut-off, especially where the strata of suitable formations are thin, the rotary works at a disadvantage. It is required to locate definitely, by the speed of drilling and the length of time it takes returns to get to the surface, various changes of formations and the depths of such changes. The testimony of drillers has shown that this is difficult to do. The time required for formation samples to be conveyed to the surface in the circulating mud increases directly with the depth of hole and thickness of mud, and inversely with the speed of circulation. Therefore, the greater the depth the greater the chance of error in making a correct log. It is required to make suitable landing of water string, in formations thus logged, depending upon the measurement of hole as shown by drill pipe. It is evident that there are many more approximations than known quantities in the foregoing, and an error of ten feet, or even five, considering the thickness of the formations sought, is enough to make the difference between success and failure.

In view of the fact that 50 per cent of the rotary jobs in the Sunset field were failures, it is evident that rotary methods, with respect to the requirements mentioned, are in need of considerable study and improvement.

The following is the average thickness of strata in the Sunset field, where the most failures occurred, in which suitable formation for shut-off must be found:

Below "Lowest Top Water" and above Oil Zone A-30 feet; Below Oil Zone A and above "Upper Flowing Water"-25 feet; Below “Upper Flowing Water" and above Kinsey Sand-50 feet; Below "Lower Flowing Water" and Wilhelm Sand-40 feet. Details of the difficulties and failures incident to the drilling of certain wells in this area are given in Formal Order No. 5, Union Oil Co. well No. 7 (International), and the accompanying tables and graphics, pages 413 to 450. Complete details of oil and water zones encountered from the surface downward are given by Deputy Supervisor R. N. Ferguson in the Second Annual report.1

Diameter, Weight and Length of Casings.

One of the principal advantages of drilling claimed for rotary tools is that long water strings can be landed with a minimum use of conductor casings. The sizes of casing to be used depend upon formational conditions and the depths to be drilled. In some areas the choice of either rotary or cable method of drilling will cause no difference in the casing program to the depth of landing water string.

In order to give a more concise idea of the amount of drilling done by each method, as to depth of hole and diameter of water strings, the itemized data for these features, as shown in Tables I to V, inclusive, have been summarized in the form shown in Tables VII, VIII, IX, X and XI. In these tables segregations are made under principal headings of "Rotary" and "Cable." In the column headed "Length," the depths of all water strings have been classified in four groups, namely, those measuring 100 to 1000 feet, 1001 to 2000 feet, 2001 to 3000 feet, and 3001 feet and over. To the right of this column are other columns showing the diameters of nine different sizes of casing. The strings of 3-inch and 2-inch casing shown under Section 8, T. 3 S., R 9 W., S. B. B. & M., Table I, are not included. The number of water strings landed by either tool, in any field, for each depth group are shown in these columns. The small letter appearing at the right of each number signifies the method of shut-off, whether cement (c) or formation (f). The data of this further classification will be discussed later under method of shut-off.

'Second Annual Report, Bull. $2, Cal. State Min. Bur.-Sunset field-pp. 234 to 239.