Eastern Shelf Exploration LLC
9405 Crowley Road Suite "C" , Fort Worth, Texas, United States

In 1987 Ed L. Dillon began developing a series of maps showing the structure of the Middle Permian along the Eastern Shelf using data acquired from over 2,400 stratigraphic tests combined with correlations from wildcat and development well logs over the same area. Deeper structures and reefs are reflected in the overlying Middle Permian throughout the Eastern Shelf. As a result, these maps are invaluable in originating new plays, planning exploration programs, correcting seismic data for velocity variations in the upper Permian, and as a factor in evaluating the probability of a seismic or subsurface prospect being present before drilling. The maps are an excellent tool for selecting areas for new "3-D" seismic exploration programs. Concurrent with the completion of the Middle Permian Basin mapping project ESP prepared a set of Siluro-Devonian structure maps covering the deeper Delaware Basin, and incorporating data from some 2,200 miles of CDP seismic. These maps are used for both prospect generation and evaluation in this basin.

ESPs Services

ESPs services include prospect generation, the review of outside generated prospects, recommendations concerning exploration programs, and geological consulting.

Basic Principle:  

The depositional and tectonic history of the Eastern Shelf of the Midland Basin is uniquely suited to the localizing of deeper structural and reef prospects by mapping the structure of Middle Permian beds easily reached by shallow stratigraphic tests, or "core holes".  A major unconformity exists below the lower Pennsylvanian sediments. The Pennsylvanian rests directly upon the eroded Ordovician Ellenburger over much of the area, although in places a thin remnant of Mississippian lies between the Pennsylvanian and Ordovician. The lower Pennsylvanian was deposited upon a gently undulating eroded surface, with the exception of some narrow grabens that formed along the east side of the Eastern Shelf as part of the north trending flexure that lies between the deeper Midland Basin to the west, and the Bend Arch to the east.  Recurring gentle uplift of many of the eroded pre-Pennsylvanian structures took place during the Pennsylvanian and influenced the deposition of cleaner carbonates or the growth of reefs in association with the slightly shallower waters. This is the reason for the occurrence of minor oil accumulations in the Ordovician Ellenburger dolomites beneath or near many of the producing Pennsylvanian reef fields. These gentle structural movements mostly died out during the late Pennsylvanian and early Permian, although there was additional movement sometime after the Upper Permian was deposited.  The Middle and Upper Permian that forms such excellent marker beds over the Eastern Shelf is a sequence of thin evaporates, clastics, shales, and dolomites that were deposited in shallow seas with little or no depositional dip. These beds were subsequently easily deformed by the differential compaction of the shales surrounding the Pennsylvanian reefs and the slight changes in the density of the shales over the pre-Permian structures that lie some 4,000 to 5,000 feet deeper, as well as responding to the additional post-Middle Permian movement of these structures.

Mapping Technique:

The Middle Permian marker beds that were deposited essentially flat were later tilted into a fairly uniform westerly dip of some 40 feet per mile into the deepening Midland Basin. Deeper structures and reefs are reflected as interruptions and deviations in this uniform dip. In order to map these anomalies it was first necessary to meticulously correlate the data from some 2,400 proprietary stratigraphic tests with data from the thousands of wildcats and development wells drilled over the same area. This information was recorded on industry standard map bases and contoured to define the regional dip rate and direction. A second interpretive pass was then made, studying each interruption of the regional dip to determine its probable cause and significance. Every log and scout ticket in the vicinity of each anomaly was examined, and any oil or gas shows noted. The correlations used were then validated and the anomaly recontoured, after which each anomaly was assigned a name, graded, and a brief description written. This description included a comment on the probable significance, any associated oil or gas shows, and any other supporting data such as seismic data "in house".  A total of 10 maps on Mylar film were made, each measuring about 42 by 60 inches. Contouring was done with pencil to allow changes as more data becomes available from new wells. The map scale is 1 inch equals 4,000 feet, and the contour interval is 10 feet. The area covered is from central Schleicher County to the north county line of Fisher County, and from the east line of these counties to about one-third of the way into Mitchell and Scurry Counties, Texas.  All of the producing structures or reefs within the area studied are reflected at Middle Permian level on these maps, and several hundred similar, untested anomalies have been identified.

Prospect Selection: 

Each of the untested anomalies on the Middle Permian maps is considered a lead to be investigated further. The lead is advanced to a prospect status if a study of the pre-Permian subsurface data indicates a logical interpretation can be made showing a significant structure or reef at depth. The prospect is advanced to an active status from which leasing and drilling recommendations will be made if one or more of the following conditions are met

• There are significant oil or gas shows reported in the objective formations associated with the prospect.
• There is confirmation of the structure at depth from well control nearby and on the flanks of the prospect.
• There is seismic data confirming a deeper structure or reef.
• The postulated deeper structure or reef is nearby to or on trend with a commercial producing field from a similar structure or reef, with a similar overlying Middle Permian anomaly.

To move from an active prospect status to a prospect where optioning or leasing is recommended, the following steps are taken:

• A prospect is selected from the active prospect list.

• A check is made of the land situation, using commercial land maps, to confirm that the majority of the acreage on the prospect is unleased or may be farmed in under reasonable terms.

• All logs and scout tickets on wells in the vicinity of the prospect are studied to confirm the existence of reservoir quality objective formations. One or more subsurface maps, usually on a scale of 1-inch equals 2,000 feet, are made to show the interpreted deep structure or reef. Any available seismic data is integrated into the interpretation. The shallower Middle Permian data is again validated and contoured onto the same scale base map. One or more cross sections demonstrating the prospect are constructed.

• A detailed prospect description and recommendation is prepared.

• The land situation is again checked, and then the recommendation is presented to the client.