GB1480646A - Method for measuring flowrates of fluids in a borehole - Google Patents

Abstract

1480646 Measuring fluid flow-rate electrically SCHLUMBERGER Ltd 26 July 1974 [27 July 1973] 33115/74 Heading G1N A method for measuring flow-rate of fluid in a borehole 10 using e.g. a turbine type flowmeter 22, the electrical signal from which is a substantially linear function of the flow-rate relative to the flowmeter involves making a first series of recordings of the signal 30, 31, 32 whilst moving the flowmeter down the borehole at a different constant speed V 1 , V 2 , V 3 for a respective recording of the series, each of the speeds being greater than the upward fluid flow-rate at a level A located between perforations 16 and 15 in the borehole casing 12, then making a second series of recordings while moving the flowmeter up the borehole at a different constant speed (V' 1 , V' 2 , V' 3 ) Fig. 3 (not shown) for a respective recording of the series, each of the speeds being greater than the upward fluid flow-rate at the level A. A third series of recordings of the flowmeter signal is made while holding the flowmeter stationary at each of the four levels A, B, C, D of the borehole. The results are shown in Fig. 5. For the level A, the first series of recordings gives three points 41, 42, 43 to which a straight line 47 is fitted and the second series of recordings gives three points 44, 45, 46 to which a straight line 50 is fitted. These lines have the same slope and are offset on the abscissa by a value d 1 . This corresponds to the range where the difference between flow-rate and flowmeter movement speed is insufficient to overcome the resistance to rotation of the flowmeter screw or shaft. This resistance is experienced regardless of the direction of flow relative to flowmeter movement. The value d 1 thus corresponds to twice the flow-rate threshold for which the screw would begin to rotate with the flowmeter stationary. Thus the response law of the flowmeter is represented by a straight line 51 parallel to lines 47, 50 and making an intercept S on the x-axis equal to <SP>d</SP>¢. For highest accuracy the operation may be carried for levels A, B, C to give a mean intercept value V o =1/3(d1/2 + d2/2 + d2/2). The flow-rate at each level may then be obtained by applying the response law to the screw rotating speeds obtained with the flowmeter stationary Fig. 4 (not shown). Alternatively the flow-rate at a level B, for example, is obtained by plotting the horizontal straight line from the intercept 60 on the y axis of the straight line 52 to a point of intersection with the line 51 representing the flowmeter response law. A vertical is dropped from this point to the x-axis to give an intercept point 61 representing the flow-rate V B at the level B. This flow-rate corresponds to the rate at the centre line of the well and is multiplied by an empirical coefficient 0À83 to obtain the average flow-rate at this level.