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Jonah Basin-Centered Gas Field The Jonah gas field is a basin-centered gas accumulation within over-pressured Upper Cretaceous fluvial strata of the Lance Formation and upper Mesaverde Group of the Green River Basin. Productive sandstones in the Lance Formation at Jonah are extremely tight with porosity ranging from 8 to 12% and permeability from 3 to 20 microdarcys. The left-lateral wrench fault at the southern boundary of the field may have produced fractures that are responsible for the shallower, 2,500-foot thick gas column and apparent higher permeability at Jonah compared with other parts of the basin. These natural fractures are accessed by massive frac-stimulation to achieve economic flow rates. DIRECT GEOCHEMICAL participated in an orientation survey to test for a geochemical signature over Jonah. Shallow soil samples were collected around productive (20 MMCFPD) and P & A (100 MCFPD) wells. Hydrocarbons were thermally desorbed from the soils and analyzed by GC-FID for C1-C6 components. The soils were also analyzed by Synchronous Scan Fluorescence (SSF), which detects heavier aromatic hydrocarbons associated with condensate. As indicated in Figures 1 and 2, productive areas can be readily differentiated from non-economic areas at Jonah type accumulations. |
Figure 2. Thermal desorption and GC/FID analysis reveals a higher abundance of light (C1-C3) hydrocarbons in soil over the productive well. |
Figure 1. SSF spectra of soil help to discriminate between dry and productive areas at Jonah. Soil over the productive well has a higher abundance of light (low wavelength) and heavy (high wavelength) hydrocarbons than the dry well.  |
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