This exercise was an effort to see if the NOAA EX1105 data could be used to determine seabed hazards by itself. In essence, to use the data as if it were the first pass survey in a new area that has no modern survey data.
The area that EX1105 surveyed is in the Mississippi Canyon and De Soto protraction areas. The EX1105 cruise collected bathymetry, water column, and backscatter data. All three datasets were reprocessed and interpreted. Again, this would be the exact dataset that a first pass seep survey would generate.
In a similar fashion to my previous blog I added federally mandated avoidance radiuses to the hazards and then calculated the amount of “unavailable” seafloor. These products are shown in this article. Additionally, using this calculated unavailable seafloor I then compared it to the most recent BOEM well location data to see if we can predict suitability of drilling in a block from this dataset alone.
Data came from the Okeanos Explorer EX1105 cruise in 2011. The government used this cruise to detect seeps with their (then) newly upgraded EM302 multibeam. Data quality was good however I didn't have tide data for this cruise. There are a few areas where there might be a tide bust due to this issue but it didn't effect the final products.
Backscatter was processed using a borrowed copy of Caris. I found that the geocoder engine worked best for this dataset. The areas of elevated backscatter were digitized manually and are thought to be areas of chemosynthetic communities (hardgrounds). Usually these areas were also populated by seeps. Interestingly enough it looks like the backscatter was able to discern some of the seabed infrastructure.
I have interpreted the seeps from this dataset in the past using FM midwater (for my former employer). In this experiment I used the NOAA seep dataset.
Bathymetric data is shown in the next figure. Depth ranges from about 240m to around 3000m. The bathymetry clearly shows the salt domes that the Mississippi Canyon protraction areas is known for.
Gradient was then calculated for the entire area and any gradient over 10° was assigned a 250ft buffer. Largely these areas are on the down dip side of the salt domes and alongside of Desoto Canyon (in the northeast). These avoidance areas would be client specific in a real world analysis – I figured 10° would be acceptable for this exercise.
Back scatter was processed in Caris and bright spots were digitized from the mosaic. Typically it is better to interpret from the waterfall display but I did not have that capability in this case. However large areas of possible hardgrounds were found along and near the up dip and sides sides of the salt domes. These largely coincide with seeps that were also detected during this survey. The potential hardgrounds were given a 2000ft buffer as prescribed by BOEM's NTLs.
NOAA seep data was also used in producing the exclusions areas. All NOAA seeps were given a 2000ft exclusion buffer.
The figure below is all the exclusions areas put together – gradient, hardground areas, and seeps. With additional data we could also add faults, canyons, ecology, known shipwrecks, or other seafloor conditions.
The final product is taking the exclusion area per block and comparing it to the block size. Blocks where 50% of the seafloor are unavailable to drilling are in red.
Upon generating the above map one conclusion occurred to me- the red blocks (consisting over 50% unusable seafloor)- did not have wells. Most don't have any infrastructure at all. This could mean that these blocks (all which have been leased) were later found to be unproducable due to hazards. That's a hypothesis of course – these blocks could remain undeveloped for any reason. I decided to test the hypotheses by looking at wells vs percent hazard.
In the above graph I selected percent hazards in a range of 5% and then used GIS to count the number of wells in the selected blocks. Unfortunately for my hypothesis there is no direct relationship between percent hazards and number of wells drilled. The only conclusion gained from this chart is that blocks with little hazards (0%-5%) contain the most wells.
Generally speaking it looks like it becomes difficult to place a well in blocks that have over 25% hazards. Interestingly three blocks, each with 43% unusable surface, have wells. This does bring hope to other producers with high concentrations of hazards. It should be noted, at this time, that these wells do not have pipelines reaching them.
While I didn't prove a direct relationship between percent hazards and wells I think it's clear that blocks without hazards are easier to drill. The question then becomes is it worth it to perform a pre-lease hazard survey.
Looking at the report from the Okeanos Explorer it looks like the crew accomplished this survey in approximately 12 days. A rough estimate of ship cost would probably be around 75,000$ a day on the high end. Plus there is always mobilization and transit costs. Therefore it isn't out of the sphere of possibility that a large regional survey such as this one could be conducted for less than 2-3 million dollars.
To put this in perspective I looked up the cost of the leases on the >50% hazard blocks.
| Block Number | Percent Unavailable | Cost |
|---|---|---|
| MC 36 | 55.1% | $8,000,000 |
| MC 166 | 56.0% | $35,938,136 |
| MC 294 | 53.2% | $8,750,000 |
| MC 295 | 54.4% | $3,798,777 |
| MC 297 | 52.1% | $ 313,428 |
| MC 389 | 72.7% | $2,605,555 |
Of course it is unknown the exact plans for any of these blocks. However if it is true that the amount of hazards had an impact on the decision not to produce these blocks it would seem that a pre-lease hazard survey (or just a desktop study) would be immensely valuable In the leasing process.
Again it appears that a seep survey would be a benefit to E&P operators. In this case Mississippi Canyon is well surveyed and it shouldn't be a surprise that chemosynthetic communities and other hazards exist all over the area. Where a pre-lease hazard survey (and therefore a seep survey) could be most effective is in areas where little or nothing is known – before a seismic survey. Being that seep surveys are comparatively cheap and could indicate some of the engineering challenges to be had well before any kind of design phase was started could be a real cost saving measure.
Please contact me at info@huxlabs.com with questions or comments.
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