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(SUBJECT TO REVISION) DISCUSSION OF THIS PAPER IS INVITED. It should preferably be presented in person at the New York meeting, February, 1916, when an abstract of the paper will be read. If this is impossible, then discussion in writing may be sent to the Editor, American Institute of Mining Engineers, 29 West 39th Street, New York, N. Y., for presentation by the Secretary or other representative of its author. Unless special arrangement is made, the discussion of this paper will close Apr. 1, 1916. Any discussion offered thereafter should preferably be in the form of a new paper.
The Control of Petroleum and Natural Gas Wells
(New York Meeting, February, 1916)
It is the purpose of this article to describe methods recently introduced into the oil and natural gas industry to safeguard the lives of the workmen and to protect property from destruction. Only such drilling methods are described as pertain directly to the operations necessary to maintain the well under complete control at all times.
Wells Formerly Drilled Without Controlling Equipment
It may seem incredible that practically all wells, until recently, were drilled without the provision of any means for control. To drill a hole into a boiler carrying high-pressure steam without first providing means to control the escape of steam would be unthinkable, yet in oil fields wells are drilled into a gas or oil formation with a possible pressure of 300 to 1,800 lb. per square inch and a daily flow of 20,000,000 to 80,000,000 cu. ft. of gas or 1,000 to 15,000 bbl. of oil per day. Some wells have produced in excess of 100,000 bbl. of oil per day, but these are exceptional
In addition to the loss of product, one must consider the great danger attendant upon the promiscuous liberation of such an amount of explosive and inflammable substance.
Introduction of Metal Casing for Deep Drilling
The introduction of metal casing to secure a permanent and impervious wall in a well made the drilling of deep wells possible and removed many of the original problems encountered in well drilling, but it did not insure the control of the well. To obtain the full value of the casing it was essential that a pressure-tight joint be made between the wall of the well and the lower end of the casing. Many materials in various forms were used, including cotton, hemp, stable refuse, oats, rice, cloth, leather, cork, rubber, lead, clay and cement, resulting, after a slow process of evolution, in the general adoption of two types of bottom fittings for
* Petroleum Engineer,
casing. These are the "long shoe," having a diameter approximately that of the casing couplings, and fitting into a hole especially prepared to insure a solid and close contact; and the rubber “packer," consisting of a rubber cylinder forced into tight contact with the wall of the well and the exterior of the casing respectively.
The other materials mentioned are used now only under special conditions, except clay and cement, each of which is used extensively, generally in combination with either the long shoe or with a packer.
Under general conditions, the weight of the casing, together with the friction between the casing and the walls of the well, is sufficient to withstand the lifting force of the gas or oil. The friction between the casing and the walls of the well is likely to vary greatly, and is uncertain at best. Additional friction is often obtained by cementing the casing within the well, and where very high pressures are encountered it is customary to secure together the several strings of casing by means of clamps, thus adding the weight of the outer strings of casing, as well as the friction, to that of the inner string.
Another practice is to bury heavy wood sills some distance below the derrick floor and, by means of heavy anchor bolts and suitable clamps, make connection to the top of the casing.
Gate Valve Does not Insure Control
With the bottom of the casing securely in place, and forming a pressure-tight, non-leaking joint, the top of the casing remains to be considered in the matter of control. Valves of various types were tried, and while not accomplishing as much as was desired, they were in many cases a necessity.
In its highest form, this type of equipment consisted of a gate valve, of inside diameter greater than that of the casing, surmounted by the casing head, the two being connected by a short nipple.
short nipple. This arrangement provided the usual casing head to which flow connections could be made and through which the usual drilling operations could be conducted. In addition, the gate valve furnished means by which the well could be shut in when the drilling tools were removed.
It was thought by many that a gate valve so placed on the head of a well insured control, but in practice many failures of this arrangement demonstrated that it did not safeguard either life or property and really caused a false feeling of safety. In fact, because of inability to close the valve promptly at a critical moment, oil or gas has become ignited and burned with great violence, making approach to the well impossible. The gate valve had to be removed by shooting off with a cannon ball, or other means, before the well, thus supposedly safeguarded, could be brought under control.
Requirements for Efficient Controlling Device
A proper closing and controlling device for the head of an oil or gas well must meet the following requirements: It must permit all drilling operations to be carried on without interference; permit of immediate and tight closing; control the flow without back pressure; insure safety to workmen; be simple in construction; compact in size; sufficiently strong to control maximum pressures; proof against injury in handling; unaffected by sand; and unaffected by fire.
FIG. 1.-OIL WELL FITTED WITH Flow LINES BEFORE "DRILLING IN." GATE VALVES ARE PLACED ON Each BRANCH OF THE Flow LINE BUT THE WELL ITSELF IS WITHOUT MEANS OF CONTROL. THE COMMON CASING HEAD is CAPPED WITH A SEPARATE TOP WHEN Flow PRESSURE SUBSIDES SUFFICIENTLY TO PERMIT.
The Control Casing Head The "control casing head,” combining the functions of a gate valve and a casing head, was designed to meet these requirements, which are considered necessary to safeguard life and property during the operations of well drilling.
This device is similar in general appearance and size to the common type of casing head in general use (Fig. 2). It can be placed above or below the derrick floor, at the will of the operator, and is arranged to receive the standard fittings commonly used with casing heads. The top opening is threaded to receive a drilling nipple or other top connections usually employed in gas wells.
The interior of the head is bored out to a true cylindrical form into which is closely fitted the plug or valve (Fig. 3). This valve is open at one end to provide a lateral passage for the oil or gas; the other end is
reduced in diameter to form a stem, which extends through a suitable stuffing box, and by which the valve may be operated. On the stem side of the valve a flat surface, or flange, fits closely against the base of the stuffing box, making a tight joint, thereby to a large degree relieving the stuffing box of duty in preventing leakage. The extending stem is hexagonal in form to accommodate a wrench, but a transverse hole through it provides a more convenient means of operating by use of a bar of iron, such as a bolt or piece of 1-in. pipe.
To provide for the convenient operation of the valve at a distance, when the casing head is below the floor or is otherwise not readily accessible, the end of the stem is bored out and threaded to take an extension of standard 2-in. pipe.
The back of the valve is broad enough to close completely either top
Fig. 4.—PHANTOM VIEW SHOWING Top OPENING CLOSED TO DEFLECT FLOW INTO TANK. THE DRILLING LINE IS SHOWN IN Position IT ASSUMES WHEN VALVE IS CLOSED WITHOUT WITHDRAWING THE DRILLING Tools.
or bottom opening in the body, and provide sufficient lap to prevent leaking.
On each side of the back of the valve is a groove, or notch, of sufficient size to encompass the drilling line, sand line, or torpedo line. By this provision the valve, when closed, while completely shutting in any flow, does not injure the line.
By means of the end opening, as well as by recessing the back of the valve, the pressures within the casing head are to a large degree counterbalanced, making the operation of the valve easy.
The device is simple, consisting of but four pieces, and having but one