Production logging in high angle and horizontal wells that produce mixtures of fluid phases is challenging because of the associated complex flow regimes that radically change the physics and technology of measurement. Depending on the borehole deviation, the velocity and fluid holdup of different phases can change dramatically for a given flow rate.
In this paper we present field examples illustrating the use of advanced logging technology and measurement techniques for well & reservoir surveillance in a mature field setting. Realizing value through surveillance using the appropriate technology is the common thread that binds these well intervention examples together.
The first field example illustrates the effective use of a compact, integrated production logging tool that incorporates several technological advances and best practices to address complex production logging requirements. The example demonstrates the added value of this new tool in terms of being able to obtain a comprehensive flow diagnosis in an environment where a conventional production logging toolstring would not have provided the data to meet this objective. The particular logging tool described in this paper provides a recording of holdup and velocity profiles along the vertical diameter of the borehole cross-section. The direct measurements of the fluid velocity and holdup enhance the capability of the petrophysicist to determine an accurate downhole flow profile. Three sensor arrays consisting of six optical probes, six electrical probes and five spinners are spread across the wellbore on retractable arms that can be opened and closed with a hydraulic sub to better locate holdup interfaces. This collection of sensor arrays, all integrated into a single sonde, makes it possible to accurately detect and measure the flowrates of each phase even in very high water-cut wells with trace oil and high gross flowrates.
The second and third field examples in this paper illustrate the use of a fit-for-purpose oxygen activation technique for positive identification of water movement behind pipe. It is not uncommon to find channels behind pipe that allow communication due to poor cement quality. Any successful water shut-off requires good zonal isolation and such flow behind pipe techniques offer a clear diagnostic value. Measurements and interpretation using this technique in two different settings are presented and discussed.
The construction of horizontal wells and subsequent re-entry into horizontal drainholes is today a feasible option with the use of sophisticated directional drilling and measurement-while-drilling techniques. However, a horizontal well is never truly horizontal along its whole length; it varies in true vertical depth along the trajectory. A departure of only a few degrees from the horizontal creates sufficient highs and lows to result in a flow profile which is challenging to understand. These undulations in a horizontal well's trajectory also result in the accumulation of fluids across local water sumps and in gas traps at local highs along the wellbore which influence the fluid movement into and along the wellbore. This in turn impacts the well's productivity and other parameters such as skin factor.