ACCESS NUMBER: M13PX00068

STUDY TITLE: Pressure Wave and Acoustic Properties Generated by the Explosive Removal of 

Offshore Structures in the Gulf of Mexico 

REPORT TITLE: Pressure Wave and Acoustic Properties Generated by the Explosive Removal of 

Offshore Structures in the Gulf of Mexico 

CONTRACT NUMBER(S): M13PX00068 

SPONSORING OCS REGION: GOMR 

APPLICABLE PLANNING AREA(S): East; Central; West 

FISCAL YEAR(S) OF PROJECT FUNDING: 20132016 

COMPLETION DATE OF REPORT: February 8 2016 

COST(S): (BY FISCAL YEAR); CUMULATIVE PROJECT COST: FY 2014: $22,495.53; FY 2015 

$59,988.09; FY 2016 $67,486.60; Cumulative project cost: $149,970.22 

PROJECT MANAGER(S): Mary Jo Barkaszi 

AFFILIATION (OF PROJECT MANAGER): CSA Ocean Sciences, Inc. 

ADDRESS: 8502 SW Kansas Ave, Stuart, Florida 34997 

PRINCIPAL INVESTIGATOR(S)*: Mary Jo Barkaszi, Adam Frankel 

KEY WORDS: 

BACKGROUND: Under the OCS Lands Act (OCSLA), the Bureau of Ocean Energy Management 

(BOEM) establishes decommissioning obligations to which an operator must commit when they sign an 

offshore lease, which includes the requirement to apply for and obtain a permit for subsequent removal of 

wells and facilities. The Bureau of Safety and Environmental Enforcement (BSEE) is responsible for 

regulating the decommissioning of OCS facilities in accordance with 30 CFR 250 Subpart Q. 

Decommissioning of these structures may be accomplished using mechanical or explosive severance 

techniques. Explosive severance relies on the use of specially designed charges to produce enough 

energy to completely sever the structure’s bottom-founded components. 

In the past, National Marine Fisheries Service (NMFS) typically applied take-threshold criteria for 

explosives from models that were developed for the incidental-take authorization of U.S. Navy’s “shock 

trials”; wherein, large, open-water charges of 5,000 to 10,000 lbs are detonated within close proximity of 

new classes of warships to assess how well the ship can withstand damage and how well the crew can 

respond to mass system casualties (Department of the Navy, 1998, 2001). Conventionally, these 

conservative predictions of the impact zone have been used to satisfy Marine Mammal Protection Act 

(MMPA) and Endangered Species Act (ESA) requirements. However, explosive severance and, 

particularly, below-mud-line (BML) detonations are likely to produce lower pressure levels at the same 

propagation distances than open-water shock trial configurations due to absorption, attenuation of energy 

by sediments, and the confinement of the explosion within well casings and platform piles. Conservative 

take estimates and large exclusion zones have been used for explosive severance due to a wide range of 

probabilistic error associated with insufficient in situ measurements from which to calculate the most 

plausible impact zone. By collecting acoustic data under various settings (e.g., varying cut depth, charge 

size), more accurate estimates of Pressure Wave and Acoustic Propagation (PWAP) can be calculated to 

apply appropriate mitigations to protect marine mammals and sea turtles, while also optimizing operations 

(safety and efficiency) during detonations. 
    ACCESS NUMBER: M13PX00068

Before this study, Minerals Management Service’s Technology Assessment and Research (TAR) Project 

funded three similar, in situ PWAP projects. The first, TAR Project No. 118, conducted measurements of 

27 separate severance detonations for West Delta (WD) Block 30 structures during the winter of 1988 

(Connor, 1990). The second, TAR Project No. 429, centered on development of improved, linear shaped 

charge cutters; however, the project was modified during field testing to allow for deployment of an 

acoustic array to measure pressure wave characteristics (Saint-Arnaud et al., 2004). The third, TAR 

Project No. 570, collected data to determine the effect of placement depth of the severance charges (15, 

20, 25, and 30 ft BML) on the recorded PWAP (Poe et al., 2009). 

Data collected from the studies resulted in a model developed by ARA (2002) referred to as the 

Underwater Calculator (UWC). The UWC is a spreadsheet-based tool that calculates the underwater 

shock wave, specifically the peak pressure, impulse, and energy flux density expected to result from the 

explosive detonation charges during explosive severance work. The tool is used to calculate the range 

from the explosive to a specified peak shock pressure and energy level that may result in impacts to 

marine life. Version 1 of the calculator (UWCv1) is based on physics models, whereas version 2 

(UWCv2) employs curves fit data from the in situ sampling at two specific locations 

OBJECTIVES: This study was developed to be a successive project and so applied a comparable 

methodology and equipment used in previous explosive severance studies to collect measurement data. 

The primary objective of this study, where possible, was to obtain additional in situ data points and 

charge parameters necessary to fill in information gaps from the previous projects. A secondary objective 

of this project was to provide supplemental data for the validation and fine tuning of previously developed 

modeling used to establish impact zones for mitigative monitoring needed during decommissioning 

projects using explosives. 

DESCRIPTION: Platform targets were selected based on consultation with BSEE and platform 

owner/operators to identify platforms that would be the best to use for model verification while still 

conforming to their decommissioning schedule. The goal was to choose targets that would allow 

numerous detonations and charge configurations such that the data collected would maximize charge 

types and BML configurations identified as high priority data gaps for refining the UWCv2. Targets were 

prioritized to increase the number and type of detonation (shot) measurements as inputs to the UWCv2, 

thus strengthening the UWC’s value for potential use in estimating peak pressure and protected species 

safety zones during decommissioning activities that use explosive severance. 

SIGNIFICANT CONCLUSIONS: UWCv1 returned accurate predictions of the results from this study 

but overestimated the measurements from Connor and TAR 570 projects. UWCv2 predicted a faster 

decay rate than was shown in the in-situ measurements. However, both the UWCv1 and UWCv2 

predictions will produce safety ranges that are smaller than those for an open-water explosion. The 

observed data from the current experiment were accurately predicted by UWCv1. As with the Connor and 

TAR 570 data, the UWCv1 generally over-predicted the actual measured PWAP levels. 

STUDY RESULTS: The predictions of UWCv2 had a quicker decay rate with range than both the 

UWCv1 predictions and the measured data from the current study. These results suggest that the effects 

of the differing structural and environmental combinations are not fully incorporated into the UWCv2. 

The implications for applying either UWC for determining exclusion zones and impact assessment from 

decommissioning events lie in the utility of these calculators in predicting the impulse, EFD, and peak 

pressure at given distances from the platform. For impulse, EFD, and peak pressure, the measured 

attenuation was consistently better fit to the predicted values produced by the UWCv1 rather than the 

UWCv2. Measured peak pressures were consistently lower than those predicted by UWCv1, but were 

variable in comparison to UWCv2, with closer distances being over predicted and farther distances being 

under predicted. UWCv1 provides a consistently more conservative and accurate prediction of measured 

values important in impact evaluation. 
    ACCESS NUMBER: M13PX00068

All predicted and measured pressure level data for the BML detonations were lower than the predicted 

amplitudes of an open-water charge for all charge weights, indicating that using an open-water model 

calculation to establish take or safety zones would consistently overestimate the size of the impact area 

for detonations at any charge weight or depth BML. The conservative estimates from both UWCv1 and 

UWCv2 provide impact zone predictions that remain far below calculations for an open-water blast. 

Peak pressure (psi) and EFD are the dual criteria typically used by NMFS in determining impact zones 

and take estimates for marine mammals and sea turtles from explosive sources. Measured psi values 

during this study were always lower than unconfined, open-water predictions for either UWCv1 or 

UWCv2. The data collected during this study can be applied for updating the UWCv2 model. 

STUDY PRODUCT(S): Barkaszi, M.J., A. Frankle, J. Martin, and W Poe. 2016. Pressure wave and 

acoustic properties generated by explosive removal of offshore structures in the Gulf of Mexico. U.S. 

Dept. of the Interior, Bureau of Ocean Energy Management, Gulf of Mexico OCS Region, New Orleans, 

LA. OCS Study BOEM 2016-019. 62 pp. 

Map showing area of study (PWAP WD40)