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Abstract The high-pressure gas in underground reservoirs can be used to provide the energy to pump brine underground and away from a well, thereby preventing premature watering out of water-drive gas wells. Use of such work has been demonstrated with modified 5-in turbine pumps acting as motors in an above-ground 500-gallon system. Such pumping work can also be used in secondary recovery of petroleum and in recovery of dissolved or hydrated natural gas. Introduction The US Hydrocarbon Potential If Power Were Available Downhole - The difficulties of getting power downhole often frustrate the use of downhole pumps and other potentially useful equipment for improved recovery of hydrocarbons in geological formations near a well. Examples include:Watered-out gas: If brine could economically be pumped out of a gas well as it was watering out, gas which would otherwise be trapped might instead be recovered. Such water removal might be to the surface or into an underground formation.Widely repeated estimates suggest that roughly 50% of the original gas is still left in the now-dying gas fields of the US Lower 48. It is not clear yet how much of the bypassed gas in watered out wells could be recovered in this way, but the potential may be as high as 100 TCF (a 5 yr US supply).Gas dissolved in deep brines, especially hydrostatically pressured brines: Only in Japan has dissolved gas been recovered in significant amounts from brine. There are very large amounts of natural gas dissolved in hot brines of deep, porous formations such as those of the US Gulf Coast and elsewhere—where deeply buried silts in porous formations are being thermally decomposed to methane, the brine above usually must become saturated with the escaping gas. If such Gulf Coast brine were (i) pumped into deep wells, (ii) decompressed in the wells to release dissolved gas, and (iii) reinjected downhole, then (iv) very large amounts of gas would become deliverable to the US Lower 48. [For reference, the geopressured-geothermal (GPGT) brines represent a part of this dissolved-gas resource but perhaps the least important part—GPGT conditions tend to block permeability and concentrate salt, which reduces gas solubility. Furthermore, if GPGT brines are brought to the surface and cooled they can be extremely difficult to reinject for disposal.] Estimates of the recoverable gas from Gulf Coast brines using GPGT technology have varied widely, 49,000 to 7 TCF as it became recognized both that the formations selected for experimental tests did not provide artesian flow sufficient for economic usefulness and because of the other difficulties with gas recovery and spent-brine disposal. Despite the GPGT problems and based on both the known solubility of methane in brine and the formation characteristics, calculations indicate the real existence of a resource base of over 10,000 TCF of dissolved natural gas beneath the land and water of the US Gulf Coast region. In other terms the natural-gas solubilities are like one TCF per cubic mile of brine and like 25 to over 100 SCF of gas per barrel of brine at depths of interest. P. 47^ |
