An Active Return Flowline Sensor for Onshore Drilling Rigs

Abstract

This paper presents the concept, construction, and test of a small scale volumetric flow rate sensor using the simple principle of mass conservation with the purpose of accurately measure the flow return in onshore drilling operations. The results demonstrate that the solution is accurate, extremely sensitive to flow variations, and capable of identifying and measuring flow variations caused by influx or loss of fluids in the wellbore. The solution uses the principle of mass conservation and is limited to low compressibility fluids which corresponds to the larger portion of onshore operations in US and abroad. Under this assumption, the principle of mass conservation is replaced by volume conservation, which allows the appropriate measure of the return flow rate. The principle is realized using off-the-shelf equipment. The solution is installed as a bypass of the regular flowline on conventional drilling rigs and does not require the use of special equipment like rotating head and expensive Coriolis systems. The small-scale sensor system constructed and tested is capable of handling up to 40 gpm with a footprint of about 4 ft2. Considering the scale to handle typical flow rates up to 1,000 gpm the size of the equipment in real scale is roughly in the linear ratio of three, which corresponds to a footprint of 36 ft2 (3’x12’), compatible with the available area between the rig structure and the mud pits. Several tests indicate that the system can sense changes in flow rate in the range of ±1% of the maximum nominal flow rate in few seconds after a flow perturbation/variation occurs and obtain accurate readings of the actual flow rate in less than 30 s (5 s to identify, 10 s to measure, 15 s to stabilize). This means that the time to identify influx of gases or loss of fluid is reduced substantially compared to traditional differential methods used in onshore rigs, and are comparable to solutions using Coriolis methods, at a fraction of the cost. The system can also provide a real-time measurement of the return fluid density. The use of this system in onshore rigs brings to these scenarios the same level of safety as the case of offshore operations using Coriolis systems. This new measuring system uses sound principles and is implemented using off-the-shelf equipment, although for higher efficiency and optimized reliability the use of a design-for-fit equipment is advisable. The invaluable benefit is to bring the same level of safety as the case of more expensive systems usually affordable only in offshore scenarios. By reducing substantially the influx volume of kicks or the volume of fluid lost before appropriate actions are taken makes this system economically and environmentally attractive.