Oil recovery experiments using Bacillus licheniformis JF-2 (ATCC 39307) and a sucrose-based nutrient were performed with Berea sandstone cores (permeability 0.084 to 0.503 "m [85 to 510 md]). Oil recovery efficiencies for four different crude oils (0.9396 to 0.8343 g/cm3 [19.1 to 38.1 ° API]) varied from 2.8% to 42.6% of the waterflood residual oil. Microbial systems reduced interfacial tension (IFT) ... 20 rnN/m [ ... 20 dyne/cm] for all oils tested. After the microbial flood experimentation, organisms were distributed throughout the core, with most cells near the outlet.
Crude oil/brine/rock interactions can lead to large variations in the displacement efficiency of waterflooding, by far the most widely applied method of improved oil recovery. Laboratory waterflood tests show that injection of dilute brine can increase oil recovery. Numerous fields in the Powder River basin have been waterflooded using low salinity brine (about 500 ppm) from the Madison limestone or Fox Hills sandstone. Although many uncertainties arise in the interpretation and comparison of field production data, injection of low salinity brine appears to give higher recovery compared to brine of moderate salinity (about 7,000 ppm). Laboratory studies of the effect of brine composition on oil recovery cover a wide range of rock types and crude oils. Oil recovery increases using low salinity brine as the injection water ranged from a low of no notable increase to as much as 37.0% depending on the system being studied. Recovery increases using low salinity brine after establishing residual oil saturation (tertiary mode) ranged from no significant increase to 6.0%. Tests with two sets of reservoir cores and crude oil indicated slight improvement in recovery for low salinity brine. Crude oil type and rock type (particularly the presence and distribution of kaolinite) both play a dominant role in the effect that brine composition has on waterflood oil recovery. v ACKNOWLEDGMENTSThis work was funded by the
Methane hydrates are methane bearing, ice-like materials that occur in abundance in permafrost areas such as on the North Slope of Alaska and Canada and as well as in offshore continental margin environments throughout the world including the Gulf of Mexico and the East and West Coasts of the United States. Methane hydrate accumulations in the United States are currently estimated to be about 200,000 Tcf, which is enormous when compared to the conventional recoverable resource estimate of 2300 Tcf. On a worldwide basis, the estimate is 700,000 Tcf or about two times the total carbon in coal, oil and conventional gas in the world. The enormous size of this resource, if producible to any degree, has significant implications for U.S. and worldwide clean energy supplies and global environmental issues. Historically the petroleum industry's interests in methane hydrates have primarily been related to safety issues such as wellbore stability while drilling, seafloor stability, platform subsidence, and pipeline plugging. Many questions remain to be answered to determine if any of this potential energy resource is technically and economically viable to produce. Major technical hurdles include:methods to find, characterize, and evaluate the resource;technology to safely and economically produce natural gas from methane hydrate deposits; andsafety and seafloor stability issues related to drilling through gas hydrate accumulations to produce conventional oil and gas. The petroleum engineering profession currently deals with gas hydrates in drilling and production operations and will be key to solving the technical and economic problems that must be overcome for methane hydrates to be part of the future energy mix in the world. Introduction Natural gas hydrates consisting mostly of methane have been identified in numerous locations in permafrost regions of the Arctic and beneath the sea floor along outer continental margins of the world's oceans. The evidence for gas hydrate accumulations has come from direct sampling in a few wells in Arctic permafrost regions, mostly North Slope of Alaska and the Mackenzie Delta in Canada, and from seafloor cores taken as part of the Ocean Drilling Program in numerous locations in ocean margins and most recently by Japan in the Nankai Trough, offshore Japan. Gas hydrates have been inferred to occur in about 50 locations worldwide as depicted in Figure 1. Mostly the evidence is indirect and inferred from seismic reflections, well logs, drilling data, pore-water salinity data, and a few direct observations in cores. A good review of the current evidence is presented by Collett.1 In a recent paper discussing the estimates of worldwide gas hydrate resources,2 it was argued that there was still no clear cut convergence of estimates over the last twenty years and that the number of estimates is so small that serious doubt can be raised about the inferences drawn from the estimates. Hence, much research lies ahead to obtain a trustworthy estimate of global gas hydrate resources. However, the enormous estimates of 200,000 Tcf for the United States and 700,000 Tcf worldwide are so large that interest continues to be very high in methane hydrates as a potential resource.
This report was prepared as an account of work sponsored by an agency of the United States Government. Neither the United States Government nor any agency thereof, nor any of their employees, makes any warranty, express or implied, or assumes any legal liability or responsibility for the accuracy, completeness, or usefulness of any information, apparatus, product, or process disclosed, or represents that its use would not infringe privately owned rights. Reference herein to any specific commercial product, process, or service by trade name, trademark, manufacturer, or otherwise, 4oes not necessarily constitute or imply its endorsement, recommendation, or favoring by the United States Government or any agency thereof. The views and opinions of authors expressed herein do not necessarily state or reflect those of the United States Government or any agency thereof." This report has been reproduceddirectly from the best available copy. Available to DOE and DOE contractors from the Office of Scientific and Technical Information, P.O. Box 62, Oak Ridge, TN 37831; prices available from (615)576-8401, FTS 626-8401.
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