uIntroduction

uFigure captions

uToltec lease

uMitchell lease

uConclusion

uIntroduction

uFigure captions

uToltec lease

uMitchell lease

uConclusion

uIntroduction

uFigure captions

uToltec lease

uMitchell lease

uConclusion

uIntroduction

uFigure captions

uToltec lease

uMitchell lease

uConclusion

uIntroduction

uFigure captions

uToltec lease

uMitchell lease

uConclusion

uIntroduction

uFigure captions

uToltec lease

uMitchell lease

uConclusion

Figure Captions

Figure 1. Index map, with location of Kern River field.

Figure 2. A horizontal slice through a 3D cube of resistivity data consisting of 9000+ log traces. Slicing down through these data reveals the channels, braided stream beds, and overbank deposits that make up the Kern River Formation (KRF).

Figure 3. A-D. Outcrops of Kern River Formation, showing typical examples of the fluvial deposits of the Kern River alluvial fan. C. Cross-bedding, indicating a uniform direction of current flow to the right, separated by a conglomerate longitudinal bar deposit and suggesting water depths of up to 10 feet. D. Trough cross-bedding, medium- to coarse-grained, pebbly sand. The outcrop is well preserved because the sediments are oil-soaked. This section is stratigraphically equivalent to the middle portion of the Kern River Formation.

Figure 4. 3D model of the KRF showing lithology, oil saturation, and reservoir temperature. This type of modeling is done routinely on a field-wide level down to the individual well level.

Figure 5. Stratigraphic cross-section, TOLTEC Lease, of KRF reservoirs, showing changes in oil saturation, as well as changes in their development.

Figure 6. Well log (A), cored section (B), thin-sections (C), particle-size analysis (D), and capillary-pressure data (E) of KRF in TOL004-XTO. C.1. Calcite ‘grains’ in poorly sorted porous coarse sand. Calcite grains formed through leaching and crushing of coarse crystalline calcite cement. Scale bar is 1 mm. C.2. Poorly sorted sand with abundant kaolinite cement. Many of the fine sand and silt grains formed through leaching and crushing of coarser gains, especially plagioclase. Scale bar is 1 mm. C.3. Poorly sorted granule conglomerate. Plagioclase grains (P) show extensive leaching, and there are small patches of kaolinite cement. Scale bar is 1 mm. D. Laser particle-size analysis shows unimodal distributions with grain sizes ranging from granular to silt size. E. Overburden centrifuge capillary-pressure data show S_wir values ranging from 48% to 29%.

Figure 7. Log suite, including plots of reservoir parameters of KRF in TOL004-XTO (courtesy of Paul Harness, formation evaluation specialist). Interval in this well shown in Figure 5 and interval of log in Figure 6 are shown by vertical columns.

Figure 8. Steamflood analysis. Residual oil saturations following steamflood range from 17.8% to 25.9%.

Figure 9. Stratigraphic cross-section, Mitchell Lease, of KRF reservoirs, showing changes in oil saturation, as well as changes in their distribution.

Figure 10. Lithologic and interpretive log suite of KRF reservoirs in MIT0020 (courtesy of Paul Harness, formation evaluation specialist). From left to right, the log shows the lithology (sandstone and siltstone), a resistivity curve, and a heat-corrected permeability curve based on the conductivity measurement. Interval in this well shown in Figure 9 is represented by a vertical column. Positions of samples used in thin-section, particle-size, and capillary-pressure analyses are also shown.

Figure 11. Photomicrographs of samples of KRF in MIT0020 (A), corresponding particle-size analyses (B), and capillary-pressure data (C). A.1. Poorly sorted sand exhibiting variable porosity. Many of the fine sand grains formed through leaching and crushing of plagioclase. Leaching of plagioclase was accompanied by precipitation of kaolinite cement (red arrow). Scale bar is 1 mm. A.2. Poorly sorted coarse sand containing abundant biotite with long axes aligned parallel to bedding. Scale bar is 1 mm. A.3. Poorly sorted granule conglomerate exhibiting crushed plagioclase and fractured quartz. Prior to fracturing/crushing this sand was probably well sorted. Scale bar is 1 mm. B. Laser particle-size analysis shows unimodal distributions for all three samples and a fining-upward sequence. C. Capillary-pressure data indicate that the S_wir values for the rocks approached 12% (88% So).

Figure 12. Steamflood analysis. Results of the steamflood analysis indicate fluid recovery values ranging from 28.1 to 54.4% of the original oil in place.

Figure 13. Photograph of Kern River field in 1899.

Toltec Lease 

Changes in reservoir development and associated changes in oil saturation are shown by means of a cross-section of part of the Kern River Formation (KRF) (Figure 5). Reservoir quality is determined by core, thin-section, particle-size, capillary-pressure, and log analysis (Figures 6 and 7).  

Thin-sections reveal poorly sorted, angular arenite with significant biotite. Calcite and kaolinite may be the result of alteration by steamflood (Figure 6C). Laser particle-size analysis shows unimodal distributions with grain sizes ranging from granular to silt size. The particle size data correlate well with the capillary-pressure data (Figure 6D and E). Overburden centrifuge capillary-pressure data show S_wir values ranging from 48% to 29% (Figure 6E).  

Integration of these multiple data sets correlates very well with each other and demonstrate the heterogeneity of KRF (Figure 7). Results of the steamflood analysis demonstrate the relationship between original water saturation of the reservoir and fractional oil recovery following steamflood. Residual oil saturations following steamflood range from 17.8% to 25.9% (Figure 8). Comparison to residual oil saturations measured from logs indicates that the potential for additional recovery may be limited in this area with current production methods.

Mitchell Lease 

Changes in oil saturation and in reservoir development are shown by means of a cross-section of part of the Kern River Formation (KRF) (Figure 9). Reservoir quality is determined by log, thin-section, particle-size, and capillary-pressure analyses (Figures 10 and 11).  

Thin-section analysis indicates a poorly sorted, angular-grained arenite (Figure 11A). The sands do not show any alteration effects resulting from previous steam in the area. Laser particle-size analysis shows unimodal distributions for all three samples and a fining-upward sequence which correlates well with the thin-section photomicrographs (Figure 11B). Capillary-pressure data indicate that the S_wir values for the rocks approached 12% (88% So). Geostatistical model data indicate oil saturations in the area are approximately 40%+.

Results of the steamflood analysis indicate fluid recovery values ranging from 28.1 to 54.4% of the original oil in place (Figure 12).

Conclusion 

In comparing the two leases presented here, from the Kern River Field, with production history that has extended across  three centuries (Figure 13), we found that the reservoir rock on the Toltec  lease exhibited alteration by-products from the steamflood process that resulted in a change in rock quality. This is probably inhibiting efforts to get the higher oil recovery percentages we see in other parts of the reservoir. The reservoir rock on the Mitchell lease exhibits no alteration of the reservoir rock, has a very good permeability, and consequently a greater potential for additional oil recovery. The fact that it has not produced much in previous attempts at cyclic steaming does not appear to be a (permeability) reservoir problem. The use of focused steamflood applications and/or horizontal drilling technology may be applicable in the Mitchell lease to distribute steam to the reservoir in a more efficient and effective manner.

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