Downhole Three-Phase Flow Measurement Using Sound Speed Measured by Local or Distributed Acoustic Sensing

Abstract

In-well multiphase flow measurement continues to be a challenging task in the oil and gas industry. One promising technology to achieve this goal is the distributed acoustic sensing (DAS) system deployed downhole along a fiber. A DAS system is usually capable of measuring speed of sound (SoS) and, depending on the type of application and how the system is installed/configured, it may also measure flow velocity. In its current state, the DAS technology is still not fully explored in multiphase flow measurement for reasons including but not limited to the lack of flow algorithms and methodologies that can use measurements in a combinative and coherent approach. The current work introduces a game-changing methodology in applying the DAS and other sound measuring optical or electronic technologies to measure 3-phase flow.

The 3-phase flow measurement methodology is based on the measurements of SoS at different locations along the well where the pressure is greater than the bubble-point pressure (P>P_b) at the first location and Pb at the second location. A bulk velocity measurement is also necessary at one of the locations, preferably at the second location. The minimum required measurements to resolve 3-phase flow rates are SoS at both locations (SoS₁ and SoS₂), pressure/temperature (P/T) values at both locations (P₁, P₂, T₁, T₂), and the bulk velocity measurement at the second location (V₂). Using these measurements, phase flow rate calculations in a 3-phase flow are possible. A Lego-like approach may be used with various sensor technologies to obtain these required measurements which are then used in a consecutive manner in 2-phase and 3-phase solution domains obtained using Wood and Korteweg-Lamb equations.

The methodology is fully explained and the analytical solutions for 3-phase flow measurement is explicitly provided in a step-by-step approach. This approach provides significant advantages over the traditional methods. For example, SoS measurements along the well at multiple locations by using the same sensor technology or by combining different sensor technologies make this methodology highly flexible and applicable to custom-fit solutions. The method is independent of the sensor type as long as the sensors measure SoS, though the ideal systems that can adopt it easily and efficiently are DAS and optical flowmeters (OFMs). Additionally, a developing case history involving downhole OFMs installed in a North Sea field-wide application is discussed. The methodology may be implemented for a special case in which SoS is measured at the same location but at different times.

This new methodology in measuring downhole 3-phase flow furthers the understanding of downhole multiphase flow measurement. It can be implemented in existing wells with optical infrastructure by adding an appropriate topside optoelectronics system when needed at later phases of production.