Introduction
This handbook was prepared as a guide and reference to the field naming process at BOEM. An oil and/or gas field in the Federal OCS of the Gulf of Mexico is defined* as an area consisting of a single reservoir or multiple reservoirs all grouped on, or related to, the same general geologic structural feature and/or stratigraphic trapping condition. There may be two or more reservoirs in a field that are separated vertically by intervening impervious strata, or laterally by local geologic barriers, or by both.
BOEM's Gulf of Mexico Field Naming Committee, comprising a petroleum engineer, a geologist, and a geophysicist, assigns field names to leases with qualifying oil and gas discoveries. It reviews new producible lease and first production memoranda submitted by the District Offices, as well as well logs, geophysical data, geologic maps, and other pertinent data to establish the existence of a new field or the extension of an existing field.
Field names are assigned for a lease or group of leases so that natural gas and oil resources, reserves, and production can be allocated on the basis of the geologic framework of the unique feature that contains the hydrocarbon accumulation. The Committee strives to include all leases determined capable of producing and associated with a specific geologic structure in a single field. In the case of a common platform serving a large structure as well as a minor satellite structure, the Field Naming Committee may consider it one field. Field names may be changed at the lessee's or lessor's request when adequate geologic and/or production data would support such a change.
The new field is usually named after the area and block on which the discovery well is located. The area encompassed by a field will be revised from time to time to include additional leases on a geologic structure, leases that have been proven productive by new drilling, and to split leases into separate fields to adhere to the definition of a field.
On the following pages are twelve examples of geologic structures in the Gulf of Mexico and BOEM field designations for their overlying leases.
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* "Guidelines for the Application, Review, Approval, and Administration of the Deepwater Royalty Relief Program."
Major Points on Assigning Leases to Fields
- Structural lows are used to separate fields with structural trapping mechanisms.
- Faults are rarely used to separate fields.
- The structure or stratigraphic condition with pay having the largest areal extent on a lease determines the field expanse.
- Reservoirs that overlap areally are always combined into a single field regardless of the fact they may be on two separate structures or stratigraphic conditions. Fields are never separated vertically.
- Wells from the same platform can be in two separate fields.
- One well is rarely in two fields, i.e., a well with two completions, each in a separate field.
Outline of Examples
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Example No. |
Title |
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1 |
Salt Dome with Fault Trap Downdip on the Domal Structure Piercement salt dome with traps against the salt and a fault trap down on the flank. Traps against the salt in blocks 2, 3, and 4 have hydrocarbon discoveries. The fault trap in block 13 has a discovery. Blocks 2, 3, 4, and 13 would all be considered on the same structure and therefore in the same field. |
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2 |
Two Structural Highs with a Separating Structural Low The structural low between the two anticlinal features in this case is sufficient to designate two separate fields. |
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3 |
Series of Structural Highs Bounded by a Common Regional Growth Fault Example 3-Figure 1-Geologic Setting: Series of structural highs bounded by a regional growth fault. The highs are separated by distinct lows. Example3-Figure 2-MMS Field Designation: These three distinct structural highs would be separated into three fields - Fields A, B, and C. Example 3-Figure 3-Shifting Lease Boundaries on the Above Example: In this figure the grid is shifted slightly. The structural highs would remain separate fields, however, leases would be apportioned rather than whole leases assigned to fields; Blocks assigned to: |
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4 |
Unrelated Shallow and Deep Structures (Adding a Separate Deep Structure to Example 3) Deeper rollover structure on the downthrown side of the same regional growth fault as shown in Example 3. This structure is geologically unrelated to the above domal high. There are two options to name the field depending on the horizontal distance between the two structures. Figures 1, 2, and 3- Shallow and Deep Structures Separated Horizontally: Even though this deep structure is along and lower on the same growth fault as previously shown in Field B (Example 3), it would be considered a separate field. The two structures are separated horizontally and their reservoirs do not overlap in an areal view. Figures 4, 5, and 6 Reservoirs of Deep and Shallow Structures Overlapping Horizontally: Another example would be the deep structure shifted underneath the shallow structure. The two structures cannot be separated horizontally because their reservoirs overlap in an areal view. Example 4-Figure 2-Cross Section on Figure 1 (Example 4) and Figure 1 (Example 3). Example 4-Figure 4-Another Variation-Shallow and Deep Structures Not Separated Horizontally Example 4-Figure 5-Cross Section on Figure 4 (Example 4) and Figure 1 (Example 3). |
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5 |
Shallow Stratigraphic Trap (Bright Spot) and a Deeper Unrelated Structure This is an example of a deep structure covering a large area with a shallow stratigraphic trap above. The field name designation of a particular lease depends on the structure the wells from that lease penetrate. If only the shallow bright spot is reached, the field name is based on the areal extent of that bright spot. However, if a well on the lease also reaches the deeper larger structure, the larger structure would be the basis for the field name. A lease could initially be named by the shallow structure and later have a deeper discovery, therefore putting the lease on a larger, deeper structure. At that point, its name would change to reflect its inclusion in the larger structure. Cross Section on Example 5 (Two Separate Fields) Cross Section on Example 5 (Larger Structure - Basis for Field Name) |
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6 |
Series of Traps Against a Large Fault Without Separating Structural Lows A long fault with a series of traps against the fault. There are no separating lows between the traps; therefore, they are combined into a single field. |
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7 |
Reservoirs on Both Sides of a Large Growth Fault Normally faults don't separate fields. No matter how large a fault or vertical separation of reservoirs, if there is an absence of a separating structural low, they are considered to be in the same field. In this example, the large fault does not separate the trap on the downthrown side from the structural high on the upthrown side. Although there is a horizon break and a large vertical separation between the two pay horizons, they would still be considered the same field. |
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8 |
Multiple Stratigraphic Traps (Bright Spots) Stratigraphic bright spot reservoirs are generally considered individual fields. A couple of exceptions are: (1.) If two or more bright spots overlap in an areal view, they are grouped into a single field. (2.) If two or more bright spots are on one lease, they are usually grouped into a single field. Example 8-Figure 1-Two Shallow Stratigraphic (Bright Spot) Reservoirs Separated Horizontally. Example 8-Figure 3-Two Shallow Areally Overlapping Bright Spot Reservoirs (Single Field). |
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9 |
Subsalt and above the Salt Reservoirs (On Separate Structures) on the Same Lease Geologic setting : Two hydrocarbon accumulations on the same lease that are not related to the same structural feature. The shallow reservoir is on an anticlinal high and the deep reservoir is found below the salt, trapped against a salt weld. The reservoirs vertically overlap. MMS Field Designation: Even though these two reservoirs do not appear to be related structurally, one being shallow (6000') and above the salt, and the other being subsalt (13,000'), they would be considered in the same field. The reservoirs overlap vertically and the MMS does not separate fields by depth. If the reservoirs did not overlap vertically, the reservoirs would be in separate fields. Example 9-Figure1-Shallow Accumulation on Anticlinal Structure Example 9-Figure 2-Deep Subsalt Accumulation |
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10 |
Salt Ridges with Multiple Fields In this example, there are flank traps against a salt ridge. These traps with pay are separated by lows, and therefore are considered separate structural highs and separate fields. |
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11 |
Two Separate Structures with an Overlapping Shallow Stratigraphic Trap In this example, there are two structural traps separated by a low. These two would be considered separate fields except for an overlying shallow stratigraphic trap. A shallow reservoir overlies both deeper reservoirs, causing all three to be combined into a single field. |
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12 |
Multiple Accumulations with Different Structural Styles in a Salt-bounded Mini-basin This example contains four different hydrocarbon accumulations, each with a different structural style: a piercement salt dome with a flank trap, a fault trap, stratigraphic trap, and a trap against a salt ridge. Because of their structural size and relative positions they would be placed into three fields. Field A would be the salt dome with flank trap in Block 3. Field B would be the two traps along the fault in Block 7. Although one is a stratigraphic trap, its proximity to the fault and the structural trap on the upthrown side would cause the two to be combined. There are lows separating these two traps from the salt dome to the north and the trap against the salt ridge to the south. Field C is the salt ridge trap. |