The present invention relates to a measure¬ ment procedure as defined in the preamble of claim 1 and a flowmeter as defined in the preamble of claim 4. Especially when searching for suitable places for final placement of nuclear waste, it is necessary to obtain information as to what sort of currents are occurring in the rock and its crevasses, i.e. what are the directions and velocities of flow of the currents. In such measurements, the small volume flows and low flow rates cause problems. In prior art, a method used for determining the magnitude of flow is to separate a certain portion of a hole cut in the rock and to fill it with a suitable mixture or soluti- on. By monitoring the changes in the concentration of this mixture or solution, it is possible to measure the flow. However, this method provides no information about the direction of the flow.

Attempts to determine the flow directions in- elude the use of various marking substances whose passage in the chinks in the rock can be monitored.

A problem with all known methods for flow me¬ asurement is that they are slow. Since the rates of flow are of the order of a millilitre per hour, per- forming a single measurement generally takes months and thus getting results from a large area and mul¬ tiple bore holes is an expensive and slow business.

The object of the invention is to eliminate the drawbacks mentioned above. A specific object of the invention is to produce a new procedure and flow¬ meter by means of which it is possible to measure very small currents in a relatively short time and obtain information about both magnitude and direction of flow. As for the features characteristic of the in¬ vention, reference is made to the claims.

In the procedure of the invention, a certain longitudinal volumetric section is separated from a bore hole made in the rock and flow measurements are performed within this section. The volumetric section is divided in the longitudinal direction of the hole into sectors extending throughout the section, e.g. four 90° sectors, in such a way that the sectors form separate spaces isolated from each other in the volu¬ metric section. The sectors are then connected toget- her via flow ducts permitting free flow between the sectors. After this, by using sensors placed in the flow ducts, the water flow values, i.e. the directions and velocities of flow between the sectors are measu¬ red. Thus, the procedure of the invention is based on a solution whereby a given portion of a bore hole is divided longitudinally into parts or sectors and any currents into or out of the sectors are concentra¬ ted or collected in a suitable flow duct system so as to permit the flow in different sectors to be measu¬ red.

The flow in the flow duct is preferably mea¬ sured by generating a suitable impulse in the current and by monitoring the movement of the impulse to dis- cover the direction and velocity of the flow, which, together with the cross-section of the flow duct, can be used to determine the flow rates. The impulse used is preferably an extremely small thermal impulse, e.g. of the order of 1/1000°, whose movement is monitored. The thermal impulse must be very small to avoid produ¬ cing turbulence in the tiny currents and to ensure that the heat will not be conducted back against the direction of flow. In this way, measurements can be made on extremely small currents, of the order of one millilitre per hour.

The flowmeter of the invention consists of a long cylindrical body comprising two ring-shaped sea-

ling elements expandable by means of internal pressu¬ re, placed at a distance from each other in the longi¬ tudinal direction of the hole so that a certain volu¬ metric section can be pressure-tightly separated from the hole. Likewise, the flowmeter correspondingly com¬ prises dividing elements expandable against the surfa¬ ces of the hole, by means of which the volumetric sec¬ tion can be pressure-tightly divided into at least three, preferably four sectors extending from one sea- ling element to the other.

The sectors are interconnected via the flow ducts and an impulse source is placed at the junction of the flow ducts while each flow duct is provided with a sensor, so that when currents occur between the sectors, the flow directions and velocities of the currents can be measured from the movements of the im¬ pulses in the flow ducts.

The sectors are preferably implemented using collector pipes through which the currents entering the sectors flow into the corresponding flow ducts while the flow ducts are joined symmetrically at a common centre located outside the separated volumetric section, the impulse source being placed in said cent¬ re. Preferably the impulse source used is a hea¬ ting thermistor and the sensors are measuring thermis¬ tors capable of detecting the heat impulse transmitted by the heating thermistor.

Since there may occur large variations in the currents in different parts of the hole, which may ha¬ ve a length of thousands of metres, very large pressu¬ re variations may appear across the flowmeter. For this reason, the flowmeter, which is preferably of a cylindrical design, is provided with an open pipe or other flow duct going through the flowmeter, permit¬ ting free flow through the flowmeter between hole por¬ tions located on opposite sides of the flowmeter. This

prevents the occurrence of pressure differences across the flowmeter that could interfere with the measure¬ ment or damage the meter.

The open pipe going through the flowmeter is preferably provided with flow transmitters enabling the amount of liquid flowing through the pipe to be measured. The measurement is preferably implemented using a suitable impulse source with suitable sensors placed on either side of it to measure the direction and velocity of movement of the impulse.

The measuring procedure and flowmeter of the invention have significant advantages as compared with known technology. Using the solution of the invention, currents of a considerably smaller magnitude can be measured than was possible to measure before. Moreo¬ ver, the directions and magnitudes of the currents both in the longitudinal direction of the hole for each section and for each sector can be measured. In addition, the measurement according to the invention can be performed considerably faster than correspon¬ ding prior-art measurements, which take about two months for each hole whereas the solution of the in¬ vention provides better and more comprehensive measu¬ rement results in less than a week. In the following, the invention is described in detail by referring to the attached drawing, in which

Fig. 1 presents the flowmeter of the inventi¬ on, partly sectioned, Fig. 2 presents a cross-section of the flow¬ meter in Fig. 1,

Fig. 3 presents a detail of the flowmeter in Fig. 1, and

Fig. 4 presents another detail of the flowme- ter in Fig. 1.

The flowmeter of the invention as presented in the drawing comprises a cylindrical shell and, pla-

ced inside the shell at its lower end and in the mid¬ dle region, ring-shaped sealing elements 5, i.e. elas¬ tic parts expandable by means of internal pressure. Between the sealing elements 5 there are four dividing elements 6 as illustrated by the cross-section in Fig. 2, i.e. four ridges or partitions extending from one sealing element to the other and dividing the space between the sealing elements into four 90° sectors. Like the sealing elements, the dividing elements are also expandable by internal pressure so that they can be pressed outwards against the surfaces of the hole under measurement.

Each sector 1 contains a flow duct 2 exten¬ ding through the whole length of the sector and having a number of apertures 11 opening into the sector.

The flow ducts 2 extend from the sectors past the upper sealing element 5 into a sensor part 12 in which, as illustrated by Fig. 3, the flow ducts join symmetrically relative to the centre axis of the flow- meter, forming between the sectors free flow links substantially free of resistance.

As shown in Fig. 3, a heating thermistor 3 is placed at the junction of the flow ducts, at their centre of symmetry, and each flow duct 2 is provided with a measuring thermistor 4 acting as a sensor, each sensor being placed at the same distance from the hea¬ ting thermistor.

In addition, the flowmeter comprises an open pipe 7 extending from end to end of the flowmeter, permitting free flow between the hole portions located on opposite sides of the flowmeter. Placed in this open pipe are a heating thermistor 9 and, at suitable distances on either side of it in the direction of flow, sensors 8 enabling the velocity and direction of motion of the heat impulse 10 transmitted by the hea¬ ting thermistor to be measured.

In Fig. 3, connected to the topmost point on

the junction of the flow ducts 2 is a hose 16 which can be opened and closed by means of a valve. The hose extends to the ground surface during measurement and it has three different uses. The topmost space in the measuring system may gather gas which is a handicap to the measurement and it can be removed through the hose 16 by opening a valve placed in the hose. Secondly, the hose 16 can be used as a duct to supply water un¬ der a suitable pressure into the section under measu- rement, thus enabling a hydraulic conductivity test to be carried out on this section. Thirdly, a pressure measurement can be performed on the measurement secti¬ on via the hose 16.

Moreover, the measuring system comprises a processor, amplifiers, filters, a magnetometer, an A/D converter and valves, said devices being placed at the upper end 13 of the system and consisting of equipment known in itself, by means of which the flowmeter is operated and the measurement results are processed in a manner known itself. Therefore, they will not be described in detail in this context. The flowmeter is connected to above-ground equipment via a cable 14 and a pressure hose 15 while the above-ground equipment comprises a suitable winch or other hoisting device for hoisting and lowering the flowmeter from and into the hole under measurement as well as a suitable mea¬ suring computer or a corresponding apparatus for pro¬ cessing the measurement data.

The flowmeter presented in the drawing is us- ed as follows.

The flowmeter, suspended by the cable 14, is lowered into the hole to be measured to a desired mea¬ suring depth, i.e. preferably to a depth at which some kind of currents are known to exist in the rock crevi- ces. After the flowmeter has been lowered to the desi¬ red depth in the bore hole, the sealing elements 5 as well as the dividing elements 6 are expanded by means

of the pressure hose 15 and pressed against the surfa¬ ces of the hole so that four sector-shaped sections are formed in the hole, said sections being tightly isolated from the rest of the hole and also from each other.

After this, liquid flow between different sectors is only possible through the flow ducts 2. Therefore, by sending a heat impulse into the liquid flow by means of the impulse source 3, the direction and velocity of motion of the heat impulse can be mea¬ sured by means of the sensors 4, allowing accurate in¬ formation about the flow rates between different sec¬ tors to be obtained. In a corresponding manner, heat impulse 10 measurement is used in the open pipe 7 to obtain flow data about the currents flowing past the flowmeter.

As the flow in this type of measurement is very small, even just one millilitre per hour, the thermal impulse also consists of a very small amount of heat. Thus, the amount of heat applied to the cur¬ rent must be small enough to avoid producing turbulen¬ ce in the current and to ensure that the heat will not be conducted back against the direction of flow. The¬ refore, the temperatures used are of the order of 1 mK.

The invention has been described above by the aid of the attached drawing, but different embodiments of the invention are possible within the scope of the inventive idea defined by the claims.