Acoustic measurement of the Deepwater Horizon Macondo well flow rate

Abstract

On May 31, 2010, a direct acoustic measurement method was used to quantify fluid leakage rate from the Deepwater Horizon Macondo well prior to removal of its broken riser. This method utilized an acoustic imaging sonar and acoustic Doppler sonar operating onboard a remotely operated vehicle for noncontact measurement of flow cross-section and velocity from the well's two leak sites. Over 2,500 sonar cross-sections and over 85,000 Doppler velocity measurements were recorded during the acquisition process. These data were then applied to turbulent jet and plume flow models to account for entrained water and calculate a combined hydrocarbon flow rate from the two leak sites at seafloor conditions. Based on the chemical composition of end-member samples collected from within the well, this bulk volumetric rate was then normalized to account for contributions from gases and condensates at initial leak source conditions. Results from this investigation indicate that on May 31, 2010, the well's oil flow rate was approximately 0.10 ± 0.017 m(3) s(-1) at seafloor conditions, or approximately 85 ± 15 kg s(-1) (7.4 ± 1.3 Gg d(-1)), equivalent to approximately 57,000 ± 9,800 barrels of oil per day at surface conditions. End-member chemical composition indicates that this oil release rate was accompanied by approximately an additional 24 ± 4.2 kg s(-1) (2.1 ± 0.37 Gg d(-1)) of natural gas (methane through pentanes), yielding a total hydrocarbon release rate of 110 ± 19 kg s(-1) (9.5 ± 1.6 Gg d(-1)).

Fig. 1.

Measured jet cross-section areas based on imaging sonar using motion tracking with a 3.5 dB (signal-to-noise ratio = 1.5∶1) threshold at a horizontal plane 3 m above the broken riser leak source (Upper), and 1.3 m above the BOP-kink leak source (Lower). X-axis values denote the sample number, with a total of 1098 cross-section measurements taken for the broken riser leak and 1,500 cross-section measurements for the BOP kink. Measurements were recorded at a rate of approximately 6 Hz, for durations of 3 min at the broken riser site, and 4 min at the BOP-kink site. The periodic variability in cross-section areas for each of the leak sites is consistent with turbulent flow.

Fig. 2.

Three-dimensional reconstruction of velocity fields based on Doppler sonar velocity field measurements recorded at the BOP-kink leak site (Upper) and the broken riser leak site (Lower). Each colored dot represents the location of a Doppler ping ensemble, with the dot color describing the estimated velocity in meters per second (as specified in the colorbar). The black ellipse in each graph indicates the calculated size and location of the leak source; blue dashed ellipses indicate the calculated flow perimeters. Black dots indicate the position of the ROV-mounted Doppler sonar during measurement.

Fig. 3.

Vertical velocity profiles of flow at the BOP kink and broken riser. A shows the raw vertical velocities for all recorded heights within the BOP plume measurement volume, B shows the calculated velocity profile at BOP-kink cross-section measurement plane using the downward-continued plume model. Velocities are binned at equally spaced intervals of 0.1 r/b_w, where -r/b_w is the region recorded between the ROV and the jet’s vertical axis, and +r/b_w is the distal region opposite -r/b_w. The number of measurements recorded within each bin is described as n, and error bars represent the standard error of the mean for each bin. C shows the raw vertical velocities for all recorded heights within the broken riser flow measurement volume, and D shows the calculated velocity profile at the broken riser cross-section measurement plane using the downward-continued plume model.