LeBLANC JR., RUFUS, Exploration Technologies, Inc., Houston, TX ; VICTOR T. JONES, III, Exploration Technologies, Inc.

Transcription

1 LeBLANC JR., RUFUS, Exploration Technologies, Inc., Houston, TX ; VICTOR T. JONES, III, Exploration Technologies, Inc., Houston, TX How to Design an Exploration Surface Soil Gas Geochemical Survey: Illustrated by Application Examples from the Hugoton Embayment of SE Colorado and SW Kansas EXTENDED ABSTRACT Three regional surface geochemical soil gas surveys covering areas of, 3, and 9 square miles were conducted in the Hugoton Embayment of southeast Colorado and southwest Kansas (Figure ). The three surveys exhibit different sampling densities and comprise both reconnaissance and detailed sampling grids. The surveys were conducted over the prolific Pennsylvanian Morrow Stateline Trend and the Permian Chase Carbonate Gas Trend of eastern Colorado and western Kansas. The stratigraphic entrapment of oil and gas in these two plays, relatively shallow depth, and highly variable porosity and permeability of the reservoirs are factors which favor the application of surface soil gas surveys as an important exploration method to reduce risk in exploration, exploitation, or development efforts in these two plays. Examples of actual reconnaissance and detailed surface soil gas surveys in this petroleum province are discussed. The surveys were conducted from 97 to 99 before there was the widespread development drilling as witnessed today. Both the advantages and limitations of soil gas surveys over the Stateline Trend from Frontera to Second Wind to Moore-Johnson fields and the area around Byerly gas field are discussed. The paper is a retrospective analysis of soil gas surveys conducted in this complex stratigraphic area in light of new geologic knowledge of the area that has been revealed in the past decade. North Stateline Trend, Morrow Oil Trend Reconnaissance soil gas surveys were conducted in the Stateline Trend area in 97 shortly after the development of SW Stockholm field and before the development of Frontera, Arapahoe, and Harker Ranch fields to the north and Second Wind field to the south. This reconnaissance survey, which consists of a grid pattern of sites per section over a -square mile area, accurately defined the general areal extent of the productive Morrow incised valley fairway in 97, well before it was confirmed by three years of development drilling that culminated in 99 (Figure ). Although this sample density did define the overall trend, it was inadequate for selecting individual -acre or 4- acre drilling sites, and for mapping the narrowest portions of the incised valley (north part SW Stockholm and Second Wind fields) where there were just too few samples to define the smaller sized reservoirs within these areas. The soil gas survey also detected microseepage from Morrow gas fields and Mississippian oil fields in the area. A detailed discussion of the relationship of the regional soil gas data with respect to these complications provides a better understanding of the relationship of the soil gas data to the subsurface reservoirs and demonstrates the value that soil gas data could have played in the development of these fields.

2 South Stateline Trend, Morrow Oil Trend Using the knowledge gained in the Stateline area, a regional soil gas survey was conducted in the south part of the Stateline Trend over a 3-square mile area with sites per section in 99 (Figure ). This density was increased still further to 3 sites per section for development drilling in the Moore-Johnson Field (Figure 3). These higher-density soil gas surveys illustrate the benefits of surface geochemistry for reducing risk in such a complex area. The highest density soil gas survey conducted for development included sites collected over a four square mile area. The integration of geochemistry with geological and geophysical data allowed a compatible, unified interpretation that indicated that the field could be extended to the north. Only one company of the several developing this field utilized geochemistry. Using this higherdensity geochemical data this company completed the first well (a 47-foot stepout) extending the field and beginning the final development. This company then completed eight consecutive successful Morrow wells in the field before drilling a dry hole, giving them an overall 9% success rate. During final development a total of 34 wells were drilled by all of the oil companies working the Moore-Johnson field. The company utilizing soil gas geochemistry acquired 47% of the reserves produced to date by only drilling 9% of the total wells. Success rates for the remainder of the other field operators were %, 3%, % and 7%. Byerly Field, Permian Chase Carbonate Gas Play Another example of a detailed regional soil gas survey, covering an area of 9 square miles, was conducted around and over Byerly gas field in Greeley County, Kansas (Figure ). This soil gas data exhibits magnitude differences that appear to depict complex porosity and permeability variations that exist within the Chase Carbonate. The variability of the cumulative gas production from individual wells in the northwest part of Byerly field was contoured and shows a pronounced northeast-southwest orientation of porosity and permeability development (Figure 4). As evidenced by the cumulative gas production contour map, there are three porosity/permeability fairways within the area of the survey at Byerly field. An ethane concentration contour map, constructed from soil gas magnitude data in the northwest portion of Byerly field shows very good correlation between areas of maximum cumulative gas production and anomalous ethane soil gas concentrations. The trends of microseep anomalies, indicated by the ethane contour map, exhibits the same northeastsouthwest orientations as seen in the contour map of cumulative gas production. Since there are many more soil gas data points than development wells at Byerly field, the soil gas anomalies, indicated by the contour map, may be providing a more realistic depiction of the subsurface porosity/permeability trends in the Chase Carbonate at Byerly field than are the less dense wells. Untested soil gas anomalies are noted to occur beyond the current limits of the field, and even more exciting localized anomalies found within the existing field appear to suggest areas of bypassed production within the known Byerly and Bradshaw field areas. Recommendations It is apparent that the most recently developed fields in the southern part of the Stateline Trend (Jace, Sunflower, Sidney) have the lowest development success rates to date. As demonstrated at Moore- Johnson field, high-density soil gas surveys could probably improve drilling success in these areas. Employment of soil gas surveys could also have accelerated the development drilling schedule at Sorrento and SW Stockholm fields from the -year period that was required for full field

3 development. An incorrect depositional model appears to be the main reason for the rather lengthy development time frame (979 to 94) required for these two fields. Success rates for Morrow exploration wells were reported to have been % in the Sorrento-Mt. Pearl-Sianna area and % in the Stateline area. There still remain areas of untested Morrow exploration potential in the transitional and updip facies tracts where soil gas surveys could be employed to improve the exploratory success rates over those previously reported. Regional isopach maps of the upper Morrow section have been used to define other areas where Morrow V, V3, and V7 incised valleys may exist. Examples presented in this paper indicate that regional soil gas surveys could be very useful in exploration ventures when used in conjunction with this method, especially in areas with sparse well control. As shown in this paper, surface soil gas geochemistry has been successfully used in developing oil reserves in the Morrow V7 incised valley trend. This method would also be applicable in other Morrow incised valley trends of southeast Colorado and southwest Kansas such as the V and V3 Valley systems. These two incised valley systems are transparent on -D or 3-D seismic due to their close proximity to the base of Atoka/top of Morrow interface. Additionally, other Morrow incised valley fill systems have been discussed in the literature in Wallace County, Kansas and farther south in Kiowa, Brent, and Powers Counties, Colorado. A high degree of compartmentalization has been observed in the Morrow V7 reservoirs in the downdip facies tract. Future soil gas surveys in this area, for development drilling purposes, should have a higher density of samples than the grid of 3 sites per section used in the 99 survey at Moore-Johnson field. For regional exploration activities in the Morrow trend, a soil gas grid of sites per section appears satisfactory only for delineating regional microseep anomalies. Soil gas geochemistry would also be applicable in other younger Pennsylvanian incised valley systems that have been identified in central and southern Kansas and northern Oklahoma. Likewise, Cretaceous age incised valley-fill systems exist in Rocky Mountain areas such as the Denver, Powder River, and Williston basins. The advantages of using each of the disciplines of geology, geophysics, and soil gas geochemistry in Morrow exploration and development are obvious, however the three disciplines are seldom used in tandem. A somewhat lesser discussed topic is that of the limitations of these three sciences. The limitations of using soil gas surveys in the Morrow oil trend have been discussed, to some extent, in this paper. Bowen et al. (993) discussed limitations of subsurface geology and -D seismic in locating reservoir quality sandstones in the Sorrento-Mt. Pearl-Sianna area. Germinario et al. (99) likewise discussed the limitations of -D and 3-D seismic surveys in locating both the incised valleys and reservoir sandstones in the southern Stateline Trend. The integrated, multi-disciplined approach of using geology, geophysics, and soil gas geochemistry (3-G Method) in Morrow exploration is a superior method whereby the advantages in one of the three disciplines complement and overcome the limitations or shortcomings of the other disciplines.

4 Summary Examples of a reconnaissance soil gas survey conducted over the Stateline Trend in 97 and a detailed soil gas survey in the Chase Carbonate Gas Trend in the vicinity of Byerly and Bradshaw fields illustrate the significant risk reduction in exploration and development drilling ventures, respectively, that can be achieved in these two stratigraphic plays. Moore-Johnson field was initially discovered by a major oil company applying conventional geology/geophysics techniques. However, development efforts ceased in 99 after drilling seven dry holes with only three producers. A second attempt to extend the field was conducted by six other companies, starting in 99. One of these companies used an integrated approach of combining subsurface geology and seismic with a high-density geochemical soil gas survey. The remainder of the independent oil companies used industry-standard Morrow exploration techniques acquired from 97 to 99 during development of Morrow oil fields to the north. A high-density soil gas survey, consisting of sites, was conducted over a four square mile area of interest. Integration of geochemistry, geology, and geophysics resulted in a compatible, unified interpretation that the field could be extended to the north. The company utilizing the soil gas survey completed the first well to extend the field with a 47-foot stepout. This company completed eight consecutive successful Morrow wells in the field before drilling a dry hole. After drilling wells, the company had a 9% success rate. A total of 34 wells were drilled by all the oil companies to both define the limits of the field and develop the Morrow reserves. By drilling only 9% of the total wells, the company utilizing soil gas geochemistry acquired 47% of the reserves produced to date. Success rates for the remainder of the other field operators were %, 3%, % and 7% There are still areas of untested potential in the Morrow oil trend. Fields discovered to date have produced. MMBO with ultimate recoverable reserves estimated at about MMBO. Fields in the southern portion of the trend are in the downdip facies tract where Morrow sands in these wider incised valleys are of smaller areal extent, smaller in cross section, and more compartmentalized. Correspondingly, the average reserves per well are smaller than in the northern fields. Although reserves are lower in the downdip facies tract, employing soil gas geochemistry appears to have the best potential for improving the relatively low success rates now being encountered in this area. This could also vastly improve the rate of return on drilling capital. This documentation of successful applications of detail soil gas surveys demonstrates how the method could be used to delineate other areas of Morrow incised valley-fill systems in areas of untested potential. Additionally, the method would also be applicable in incised valley-fill systems of other geologic ages in Mid-Continent and Rocky Mountain basins. Soil gas geochemistry is not a panacea for Morrow sandstone and Chase carbonate exploration, exploitation, or development drilling, but should be integral part of a thorough exploration program. Applying the recently related concepts of Morrow sequence stratigraphy will undoubtedly be a tremendous advantage in future Morrow exploration and development drilling ventures, reservoir maintenance, and in secondary recovery operations. Using soil gas geochemistry in tandem with this concept could provide a very powerful synergistic effect to Morrow exploration and development projects.

5 FUNK ARAPAHOE MORROW SAND TREND LAS ANIMAS ARCH STATELINE COMPLEX STOCKHOLM WEST FRONTERA Logan Co. Wallace Co. MT. SUNFLOWER TR EN D STOCKHOLM SOUTHWEST Wichita Co. CA RB ON AT E Greeley Co. CH AS E SIDNEY CARWOOD MOJO JACE AREA BYERLY EAST BYERLY JACE MOORE-JOHNSON LEOTI GAS AREA MOORE JOHNSON SOUTH LEOTI GAS AREA LEOTI GAS AR Figure. Areas of three regional soil gas surveys, Southeast Colorado and Southwest Kansas. K4 K4 K3 K K74 K73 K7 K7 K7 K9 K K7 K7 K K K4 K9 K9 K9 K9 K9 K93 K9 K K K K9 K K K7 K K43 K47 K4 K9 K K7 K74 K73 K7 K7 K7 K77 K K94 K9 K9 K K7 K3 K K49 K4 K9 K K7 K K9 K K37 K3 K3 K34 K33 K7 K7 K74 K73 K77 K K7 K K K K79 K9 K K7 K K3 K K9 K9 K9 K3 K3 K3 K3 K34 K3 K3 K3 K37 K39 K33 K33 K33 K37 K37 K373 K37 K374 K44 K3 K377 K379 K37 K3 K3 K3 K33 K47 K4 K47 K4 K43 K49 K43 K49 K4 K43 K9 K434 K4 K4 K43 K4 K44 K4 K4 K7 K49 K4 K77 K K7 K K K K79 K3 K34 K33 K34 K3 K3 KA K3 K39 K39 K394 K39 K3 K33 K3 K3 K34 K3 K3 K3 K37 K39 K33 K33 K33 K3 K37 K4 K47 K44 K44 K443 K44 K447 K37 K373 K37 K374 K44 K3 K377 K4 K4 K379 K37 K3 K3 K3 K33 K4 K47 K47 K4 K49 K493 K49 K49 K494 K43 K49 K43 K49 K4 K43 K433 K434 K437 K43 K43 K4 K4 K43 K4 K44 K4 K4 K49 K4 K47 K3 K K K K4 K7 K3 K34 K37 K3 K3 K39 K K7 K K9 K7 K7 K9 K9 K9 K9 K K9 K K K3 K K4 K43 K44 K4 K9 K97 K9 K K99 K K9 K K7 K4 K49 K K79 K3 K34 K K K4 K37 K3 K3 K39 K7 K K K3 K K4 K3 K3 K3 K K K3 K4 K K K7 K K K A. Stateline Complex Development January 97 K3 K4 K Ethane (ppb) > < K4 K K K7 K K9 K7 K7 K K4 K3 K K44 K7 K4 K K4 K9 K9 K9 K9 K K43 K K44 K3 K4 K47 K4 K4 K3 K K K K49 K4 K K K7 K77 K K7 K9 K97 K9 K99 K K K K3 K K K4 K94 K93 K K74A K73 K7 K9 K9 K K K499 K49 K497 R 4 W K47 K47 K4 K4 K4 K74 K4 K7 K49 K49 K494 K K K9 K43 K K7 K77 K K7 K4 K47 K4 K74A K94 K93 K K7 K3 K K33 K K73 K7 K9 R 43 W K47 K49 K4 K493 K449 K44 T S K K T S T S K4 K49 K447 K K K3 K74 K K4 K49 K44 K44 K3 K K K K49 K4 K47 K4 K4 K4 K4 K4 K44 K43 K33 K444 K443 T S T S T S K K3 K397 K49 K K K3 K39 R 4 W K K4 K3 K K44 R 43 W K47 K4 K49 K479 K47 K K K4 K47 K4 K44 K44 K43 K4 K44 K43 K4 K4 K4 K7 K37 K39 K394 K K K499 K49 K497 K4 K49 K9 KA K3 K393 K44 K43 K4 K47 K47 K3 K34 K344 K3 K3 K34 K4 K4 K49 K4 K47 K39 K39 K39A K39 K39 K449 K44 K439 K49 K4 K47 K4 K3 K34 K33 K3 K3 K4 K49 K44 K44 K343 K3 R 4 W R 43 W K39 K4 K444 K3 K34 K34 K334 K333 K3 K397 K37 K4 K34 K339 K33 K337 K4A K3 K34 K33 K3 K K94 K93 K33 K3 K3 K3 K33 K37 K3 K393 K9 K9 K9 K3 K37 K3 K39 K39 K39A K39 K39 K3 K9 K K7 K K K3 K34 K3 K3 K3 K47 K47 K7 K74 K73 K3 K K K K9 K K7 K K K4 K3 K33 K33 K3 K43 K4 K44 K43 K K7 K K44 K43 K437 K43 K43 K4 K7 K7 K99 K43 K433 K K K4 K K K7 K4 K4 K4 K39 K3 K34 K344 K37 K4 K4 K49 K4 K3 K4 K49 K479 K47 K343 K3 K3 K34 K4 K4 K49 K4 K47 K39 K439 K4 K34 K34 K3 K4 K4 K3 K K37 K3 K3 K34 K33 K3 K3 K39 K34 K339 K33 K337 K4 K43 K K K9 K47 K334 K333 K3 K37 K37 K K7 K9 K3 K33 K3 K3 K3 K4A K3 K4 K3 K K K K99 K K K9 K K7 K K K4 K33 K3 K3 K34 K33 K3 K9 K97 K3 K37 K K9 K K79 K K9 K33 K3 K3 K3 K7 K77 K K3 K33 K39 K9 K9 K K34 K7 K74 K73 K7 K7 K7 K9 K9 K K7 K K K4 K3 K K94 K93 K34 K33 K37 K K7 K4 K4 K4 K39 K3 K K K9 K K K39 K3 K3 K3 K99 K9 K9 K K K4 K K K7 K K4 K7 K K7 K K K3 K7 K K K4 K3 K K49 K4 K3 K3 K4 K7 K7 K K K9 K K7 K K K K K K4 K47 K4 K K94 K K K9 K47 K4 K4 K44 K43 K4 K K9 K9 K K7 K K K4 K K K4 K3 K K K K99 K4 K3 K K K K9 K K3 K3 K33A K3 K3 K3 K9 K K34 K33 K K79 K3 K K7 K K K4 K K9 K97 K97 K4 K3 K K K K99 K9 K9 K K7 K7 K K9 K3 K3 K K K7 K K K4 K3 K K K K79 K7 K77 K K7 K K K K49 K4 K9 K93 K9 K9 K9 K9 3 K4 K44 K74 K73 K7 K7 K7 K9 K K7 K37 K3 K3 K K4 K3 K4 K34 K33A K3 K3 K3 K9 K K K K94 K33 K4 K3 K4 K3 K K4 K3 K K K K99 K9 K97 K K9 K K7 K K K4 K3 K4 K39 K3 K37 K K K K49 K4 K47 K K4 K3 K K K K79 K7 K77 K K7 K94 3 K4 K K3 K3 K34 K33 K3 K3 K3 K9 K K9 K K7 K K K4 K3 K4 K39 K3 K37 K K K K49 K4 K47 K3 K3 K34 K33 K3 K3 K3 K9 K K K47 K4 K9 K K7 K3 K3 K3 K4 K49 K K K K3 K4 K K K7 K4 K7 K79 K K K3 K4 K K B. Soil Gas Survey Conducted - November 97 Ethane Magnitude Contour Map Figure. Reconnaissance soil gas survey over Stateline Complex. C. Stateline Complex Development August 99

6 S43W S43W S43W S4W A A A 49A A A KELLER # MILLER # KELLER # WILLIAM # 7 ABEL # S4W BREWER 3 A WITT A- BREWER LINN WITT B- MO-JO WITT A- BOBCAT - BREWER 4- BREWER LINN COYOTE LANG 34-3 BOBCAT - COYOTE WENDLEBURG - WENDLEBURG - HUDDLESTON 33- HUDDLESTON 34- MO-JO MO-JO 3 4 SELL BOBCAT - WENDLEBURG 3- MO-JO 4 BLACKBIRD # SELL #3-3 A AMOCO LAWSON # LIMITS OF V7 INCISED VALLEY-FILL 7 ABEL # S4W WITT A- LAWSON # BOBCAT - WITT A-.3 COYOTE WITT B- 4. BREWER 4- WENDLEBURG - WENDLEBURG 3- BREWER BREWER 3 BREWER WENDLEBURG HUDDLESTON MO-JO MO-JO 3 9 MO-JO LINN BOBCAT - LANG 34-3 BOBCAT - COYOTE HUDDLESTON 33-4 SELL MO-JO 4 BLACKBIRD # SELL #3-3 7 Scale - Feet Scale - Feet Scale - Feet ETHANE CONCENTRATIONS (ppb) > < Limits and Dimensions of Morrow V7 Sands Areal Extent Thickness Width V7d V7c V7b - 3 ft. - ft. - 4 ft. Figure 3. Moore-Johnson Field, Greeley County, Kansas - 7 ft. 3-3 ft. 3-3 ft. BOBCAT LEASE WITT "A" LEASE WITT "B" LEASE LANG LEASE COYOTE CUM. BO X B3 SS7B SS7B SS73B SS74B SS7B SSB SS77B SS7B SS79B SSB SSB SSB SS3B B3 SS4B SSB SSB SS7B 3 SSB SS9B SS9B SS9B SS9B SS93B SS94B SS9B SS9B SS9B B9 B3 B7 B 9 9 B93 B94 B7 B79 B B B 4 4 B4 B B 9 B9 B9 B9 3 B9 B9 B97 3 SS7B SSB SSB SSB SS3B SS4B SSB SSB SS97B SSB SS9B SS99B SSB SSB SSB SS7B SSB SS9B SSB SS3B SS4B SSB 4 4 SSB SSB SS3B SS33B SS34B SS7B SSB SS9B SS3B SS3B SS4B SSB SS3B SSB SS44B SS4B SS4B SS47B SS4B SS4B SS4B SS43B SS37B SS3B SS39B 93 SS3B SS3B SSB SS4B SSB SS49B SSB SSB SS9B SS9B SSB SSB SS4B SS3B SS7B SS4B B9 B7 B73 B7 B73 B7 B73 B99 B7 B B79 B7 B7 B77 B7 9 B77 B7 B74 B7 B7 9 B7 B73 B73 B74 B7 B 9 B73 B733 B B73 SSB SS9B SSB SSB SSB SS7B 4 9 B9 B93 B9 B9 B B97 B9 B94 B9 B9 4 B9 B9 B99 B9 4 4 B93 B94 B9 4 MILES CUMULATIVE GAS PRODUCTION PER WELL MMCFG >,, -, -, 3 - < 3 B9 B74 B74 B74 B74 B743 B B9 B B7 B7 B73 B74 B B3 B4 B B B7 B 4 B7 B7 B7 B777 B77 B B794 B79 B79 B793 B79 B B 4 B B B7 B B9 3 4 B B3 B4 B9 B B 7 B4 B43 B44 B4 B4 B47 B4 B4 B47 4 B4 B43 B44 B B B4 B B3 MILES B97 3 ETHANE CONCENTRATIONS (ppb) > < Figure 4. Byerly Field. 4a) Contour Map of cumulative gas production from wells of Byerly Field. 4b) Ethane magnitude contour map of Byerly Field