This invention relates to downhole tools and to a * method of operating downhole tools.

The invention is concerned particularly with downho tools adapted for running in a drillstring and operable means of the pressure of circulating fluid.

According to the present invention, there is provide a downhole tool comprising a tool body adapted for runni in a drillstring and having a passage therethrough for circulating fluid, duct means arranged for communication with the passage, and fluid control means operable selectively to open and close the duct means for switchi on and off a flow therein of part of the circulating flu from the passage; characterised in that the fluid contr means comprises a member shiftable in the passage with respect to the tool body by fluid flowing in the passage spring means acting on the shiftable member and urging t same against the fluid circulation direction, locating means engaging the shiftable member to locate same in th passage against the spring means the locating means bein adapted to operate sequentially in response to shifting the shiftable member to locate the latter at two or more respectively different positions, the shiftable member

J being adapted or arranged for opening and closing the du means.

By choice of spring strength with reference to passa dimensions and fluid viscosity and circulation rates, th fluid control means can be operated to open and close th duct means repeatedly simply by successive transient increases in circulation rate. Increase in pressure dro over the shiftable member shifts same against the spring and effects selection of the next location in sequence. Thus, an on/off use of pressure fluid to operate a tool downhole can be simply controlled by the driller from the surface.

Further, according to the present invention, there is provided a method of remotely actuating a downhole tool i a drillstring by means of a change in fluid circulation; characterised in that the change in fluid circulation comprises a transient or temporary change of fluid circulation rate by means of circulation pump means at th surface to cause shifting of a spring-biassed actuating means disposed in the tool.

Embodiments of the present invention will now be described, by way of example, with reference to the accompanying drawings in whic :-

Fig. 1 is a sectional elevation of part of a downhole tool in accordance with a first embodiment of the present invention; and

Fig. 2 is a sectional elevation of part of a downhole in accordance with a second embodiment of the present invention.

In Fig. 1 of the drawings, part of a downhole tool body is indicated by reference numeral 10 and has a passage 11 therethrough for carrying circulating fluid which is represented by arrows 12 and consists of, for example, drilling mud which, during drilling operations, is circulated downwards through the passage 11 and upwar in the well annulus at flow rates in the region of 700 gallons/min, and at pressures in the tool in the region 700 pounds/sq. in. The tool body 10 is adapted (not shown) for running in a drillstring (not shown) in conventional manner.

The passage 11 is enlarged by machine boring as at 1 to accommodate a shiftable actuating member in the form an annular piston 14 which is thus axially shiftable in the passage 11 with respect to the tool body 10. The to end face 15 of the annular piston 14 is open to pressure of fluid in the passage 11, and a ring seal 16 is provid closely below the top end face of the annular piston to provide part of valve means as will be described later herein.

The lower end face of the annular piston 14 is abutte by a spring means in the form of a coiled compression spring 17 which is retained in the tool body 10 by means of a screw-threaded collar 18. It is to be understood that the annular piston 14 is rotatable with respect to the spring 17, and in a practical arrangement a thrust washer or thrust bearing may be interposed between the

annular piston 14 and the spring 17.

The annular piston 14 is located axially by locating means m the form of a pm-m-slot arrangement using a pi 19 held radially in the tool body 10, and a slot 20 which is milled in the outer surface of the annular piston 14. An inner end portion of the pin 19 is received in the slo 20. The path profile of the slot 20 is such that the annular piston can be located at two different axial locations which are mutually spaced by the dimension D in Fig. 1. The slot 20 is continuous around the annular piston 14 and the returns in the slot path are detailed so that successive axial shiftings of the annular piston 14 against the spring 17 will cause the annular piston 14 to rotate so that the two mutually different axial locations are selected sequentially.

The tool body 10 is provided with duct means in the form of a duct 21 which extends axially through the wall of the tool body 10 and with a short radial portion 22 which emerges into the bore 13 just below the upper- position of the ring seal 16. Thus, the upper end portion of the annular piston 14 in conjunction with the mouth of the radial duct 22 constitute a valve means operable to open and close the duct 21 by axial shifting of the annular piston 14. It will be appreciated that the axial shift of the annular piston 14 required to open the duct

21 is less than the dimension D.

The duct 21 leads to a pressure fluid operable tool

(not shown) the specific nature or purpose of which is an essential feature of the present invention.

Operation of the arrangement described above is as follows. With the annular piston 14 located as shown in Fig. l, the drillstring is operated downhole in conventional manner with normal fluid circulation. The tool (not shown) to be operated by pressure fluid from duct 21 is inactive. When there is a requirement remote to activate the tool using pressure fluid from duct 21, the fluid circulation rate is temporarily or transiently increased by means of the conventional circulation pumps (not shown) thereby to increase the pressure drop over t annular piston 14 sufficiently that fluid pressure actin on the top end face 15 will overcome the force of spring 17 and shift the annular piston 14 axially downwards unt the inner end of pin 19 locates at the next return 19A o the slot 20. Then, the fluid circulation rate is reduce to normal so that the spring 17 shifts the annular pisto axially upwards until the inner end portion of pin 19 locates at the next return 19B in the slot 20. Now, with fluid circulation rate at normal, the mouth of the duct 2 has been opened to pressure of fluid in the passage 11 an such pressure fluid is conveyed by the duct 21 to operate the tool (not shown) as required. In order to stop the pressure fluid operated tool, the fluid circulation rate is again increased as previously described to operate the locking means 19, 20 to return the annular piston 14 to

the position shown in Fig. 1 thus closing the duct 21.

During operation of the pressure fluid operated tool (not shown) , the driller at the surface will be able to measure an increase in fluid pressure-drop attributable the pressure fluid operated tool and this provides an indication that the annular piston 14 has functioned.

From the foregoing, it will be appreciated that the diameter and length dimensions of the open bore through the annular piston 14 together with the strength and rate of the spring 17 will be calculated with reference to the viscosity of the drilling fluid and the circulation rates and fluid pressures to be used. Typical values for the parameters involved are as follows.

Drilling mud weight 12 pounds/gallon

Circulation rate 700 gallons/minute

Fluid Pressure in tool 700 pounds/sq.in.

Bore area of piston 14 2.4 sq. in.

Pressure drop over piston 14 94 pounds/sq. in. Force of spring 17 (relatively 240 pounds low spring rate)

Increase in circulation rate 50 g lIons/minute to shift piston 14 against (Increased rate= spring 17 750 gallons/min)

In Fig. 2 of the drawings, parts corresponding with those in Fig. 1 are given the reference numerals used in Fig. 1. In Fig. 2, the tool body 10 is provided with an annular chamber 23 in an enlarged bore portion 24 of which

is received the upper parts of a piston-sleeve 25 the lower portion (not shown) of which is associated with a tool mechanism the nature of which is not an essential feature of the present invention. Such tool mechanism i operative by downward shifting of the piston sleeve 25.

The radial duct 22 leads into the annular chamber 23 so that the piston sleeve 25 can be subjected to pressur fluid to operate same as and when required.

During operation involving use of the piston sleeve 25, pressure fluid flow through the radial duct 22 would not easily be detectable at the surface and therefore th driller would have no indication as to whether or noi th tool has been activated. To avoid this problem, the annular chamber 23 is provided with an escape port 26 in which is fitted a metering orifice 27 sized to provide a "tool-active" indicating pressure-drop at the surface without robbing the tool of significant operating pressure. Typically, a metering orifice of cross-sectional area 0.077 sq. in. would provide an indicating pressure drop of about 250 pounds/sq. in.

Modifications of the arrangements described above, within the scope of the present invention, include adaptation of the locating means so that the shiftable member has three or more mutually different locations for extending the controlling capacity of the valve means.