Acoustic doppler downhole fluid flow measurement
An apparatus and system are disclosed for in situ measurement of downhole fluid flow using Doppler techniques. First, a baseline speed of sound is established as close to the desired measurement point as possible. This speed of sound measurement is then used in Doppler calculations for determining flow velocities based from induced Doppler shift resulting from fluid flow. A heterodyne receiver arrangement is preferably used for processing so that the flow direction can be determined and the detection sensitivity for low flow velocities can be enhanced. From in situ measurements, well kicks may be spotted and dealt with in real-time. In addition, current theoretical models of rheological properties may be verified and expounded upon using in situ downhole measurement techniques. Furthermore, the velocity measurements described herein can be used to recognize downhole lost circulation and/or gas/water/oil influxes as early as possible, even when the mud recirculation pumps are turned off.
1. A method of determining downhole fluid composition in an annulus, comprising:
measuring the in situ speed of sound of fluid inside a drillstring;
measuring the in situ speed of sound of fluid in the annulus;
comparing the speed of sound measurements; and
determining fluid composition based on the comparison.
2. The method of claim 1 , wherein the measurements are made with fluid circulation stopped.
3. The method of claim 1 , wherein the measurements are made while drilling a formation.
4. The method of claim 1 , further comprising detecting an influx of fluid or gases into the annulus based on fluid composition.