David G. Koger
Consultant
Fort Worth
Dwight M. Ross III
Dwight M. Ross Drilling Co.
Wichita Falls, Tex.
This article demonstrates the effective use of remote sensing photogeology in close proximity to existing production: for identifying areas worthy of closer scrutiny, for staking new locations, and for orienting the cost-effective use of other, more expensive techniques.
Remote sensing photogeology principles and their application to frontier areas and mature basins have been discussed previously (OGJ, Dec. 5, 1988, p. 54).
Prospecting close to densely drilled, mature basin fields is risky business. Undrilled structures can elude all but the most closely spaced and expensive seismic programs, and oil once there may have been drained already.
On the other hand, such an area is proven to favor oil development, transportation is in place, and leases can be less costly.
Features present in Landsat multi-spectral scanner satellite imagery first drew attention to the areas of interest. A drillable prospect model resulted when satellite derived information, detailed subsurface geology, and seismic information were combined.
GEOGRAPHICAL AREA
The area of interest is in Texas Railroad Commission Dist. 9, bordering Oklahoma, in the northwestern quadrant of Montague County.
It is 3 1/2 miles south of the town of Nocona and 2 miles south and east of Belcherville.
The area is densely drilled, and production history is quite good (Fig. 1, table).
SURFACE TOPOGRAPHY
Surface rocks are Permian limestones and sandy shales. Soil groups are: Bastrop loams, Renfrow loams, Bontiexray complex, and Stoneburg-anocon.
Dendritic drainage patterns exhibit occasional angular deviations and bends. Vegetation includes small farming areas with various crops; native coastal pasture, small shrubs, and post oak in uncleared areas become more prominent to the east and south.
USE OF LANDSAT DATA
Landsat imagery was useful for detecting faults and fractures, which were expressed in surface topography and subtle soil and vegetation alterations. Fracture trends most often enhance production associated with traps in the area, and their relative age might be inferred from their orientation. The closed structure on the Long Branch Prospect (Fig. 2) is cut by a right angle tension-relief fault on the east side that originates from the larger east-west trending fault. Both of these faults cut the Ordovician Ellenburger, but the easternmost fault cuts only to the base of Pennsylvanian Atoka.
Landsat data often convey evidence of buried structure, (reef buildups, domes, anticlines, and so on), the surface expression of which may be: radial or annular drainages, moisture accumulation, and differential compaction; soils staining, bleaching, and variations in texture; vegetation patterns, population densities, stresses, or enrichment; and any combination of these phenomena. Structures too subtle for detection and mapping by all but the most densely spaced, cost-prohibitive survey methods can appear as variations in photo tone-if not drainage detail-in properly created satellite imagery (owing as much to extended sampling of vegetation-sensitive infrared light as to the frequency with which the satellites sample the earth in the spatial domain).
Interactive computer enhancement of multitemporal and multisensor data provides the best opportunity for discovery, delineation, and explanation of the probable origins of these tonal anomalies.
Tonal or spectral anomalies can suggest not only structure but, more importantly, possible biogeochemical alterations due to the multifarious effects of hydrocarbon microseepages.
The Landsat-defined structure was allowed (but not suggested) by subsurface data. A seismic program, designed in accordance with the remote sensing interpretation, confirmed the presence of the faulting and structure (Figs. 3, 4). Seismic interpretations were undertaken without knowledge of the features present in the satellite imagery.
REGIONAL GEOLOGY
The prospect is situated in the northern part of the Fort Worth basin, which has produced commercial quantities of oil for more than 50 years.
This basin has a large, low relief feature that is generally accepted as being Pennsylvanian Strawn in age. It is bounded to the west by the gently uplifted Bend arch, to the north and east by the steep folds and faults of the Muenster arch, and to the south by the Llano uplift or one of its salients. To the southeast, it appears to dip beneath the rocks of the Ouachita Overthrust in the vicinity of northwest Dallas County.
An asymmetrical basin, its deposits rise gently to the west and south, then very abruptly to the north and east against the Muenster arch. The deep axis of the basin is located slightly south and west of the Muenster arch. Regional dip on the Lower Pennsylvanian sediments in the north part of the basin is to the east-northeast at 80-100 ft/mile. Older horizons dip in the same direction but at a slightly steeper rate. This regional dip is frequently interrupted by closed structures, which create traps suitable for hydrocarbon accumulation.
PRODUCTION HISTORY
Sanders field, about 1 mile south of the prospect area, was discovered in 1942 with the Sinclair-Prairie 1 Sanders in Lot 114 of the J.H. Belcher Subdivision (J.H. Mattison Survey). Pay was from a conglomerate in the Atokan section at 5,961 ft. Initial flow was 375 bbl of oil in 3 hr. About 23 wells have produced 1,615,024 bbl of oil. Nine active wells produce 2,482 bbl/month. Additional production has been discovered in the Ellenburger and Ordovician Viola sections and Atokan limestone. Most wells produce 80,000-500,000 bbl of oil.
Lone Prairie field, about 1 mile southwest of the prospect, was discovered in 1950 and produces from Atokan conglomerates and Ellenburger. Total cumulative is 973,340 bbl from 20 wells, and current production is 506 bbl/month.
DRILLING RESULTS
As indicated in the remote sensing and seismic interpretations, the 1 Fenoglio, discovery well for Sandra Kay field, has closure on all four sides. It is the only Ellenburger production in the area to have come on production flowing naturally, at 73 b/d of oil through a 10/64 in. choke without water from open hole at 6,013-33 ft.
Drill stem testing and logs indicate seven or eight probable producing zones above Ellenburger.
SUMMARY
Satellite imagery was an effective tool for the delineation of faults and structure in close proximity to existing production.
Once noted, the lead was further studied with subsurface and seismic analysis, undertaken in the most cost-effective manner and orientation as suggested by remote sensing photogeology.
Copyright 1990 Oil & Gas Journal. All Rights Reserved.
