Integration of NMR with Other Open Hole Logs for Improved Porosity, Permeability and Capillary Pressure of Gas Sand Reservoirs

The deep tight sandstone reservoir is characterized by small pores, narrow throats, and poor connectivity. The wireline logging responses are so complex, and especially, it is difficult to identify fluid types by previous resistivity-porosity cross-plot method. Based on the differences of acoustic, density, and neutron logging responses in gas and water-saturated layers, some effective sensitivity factors to fluids are constructed for gas-bearing layer identification. From conventional logging principle, the acoustic-neutron porosity difference, density-neutron porosity difference, and triple-porosity ratio are all sensitive parameters to the gas-bearing layer. From the nuclear magnetic resonance (NMR) logging response mechanism, the density and NMR porosity difference, and T2 geometric mean of the movable fluid are also two sensitive parameters. Based on the above parameters, a series of fluid typing cross-plots are constructed and their adaptabilities are compared. By contrast, the interpretation result from NMR logging are better, and dual-porosity difference and triple-porosity ratio method from conventional logs are also effective when NMR logging is not available. In log interpretation, these methods are used to gives their results, respectively, and then they are combined together by vote strategy according the performance of every cross-plot, therefore, the comprehensive fluid typing method is proposed. In two case studies of Kuqa Depression of Tarim foreland basin, China, the comprehensive fluid typing method proves effective and novel, and it is another alternative method for fluid identification using non-electrical logs when the electrical logs is not available or applicable.

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Simulation on the Method of Determining Remaining Oil Saturation by Measuring Dual Pulsed Neutron Parameters

Zhang

Yuan

Liu

et al. 2011

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The parameters of C/O ratio and Sigma based on pulsed neutron source can be obtained at the same time in one logging, which utilizes a special pulse and measurement timing design to record inelastic, capture gamma ray spectra and gamma ray time spectrum at the far and near detector. By combining dual parameters for determining oil, water and gas saturation, it can resolve the problem no way to distinguish gas and water only using C/O, oil and fresh water only using Sigma, in addition, it can determine saturation under the condition of unknown borehole porosity information. By theoretical analysis and Monte Carlo simulation method, the gamma ray time spectrum after repetitive pulse of neutron emission can still meet the exponential decay law, and repetitive pulse before neutron lifetime measuring can raise gamma count rate of time spectrum 3 to 5 times, therefore, the dual parameters measured simultaneously in one logging are feasible. Through dual parameters of C/O ratio and Sigma, the C/O data is cross plotted against Sigma data and then to determine oil, water and gas saturation. By using Monte Carlo method to set up computation model, inelastic gamma spectrum, capture gamma spectrum and time spectrum under certain borehole and formation conditions can be simulated, and the logging response is given when determining oil, water and gas saturation by using cross plot technique of C/O and Sigma. In addition, the influence of lithology, porosity, shale content, borehole size, formation water salinity and gas density on determining saturation were simulated, and it will provide response relation for determining oil saturation by dual parameters of C/O ratio and Sigma.

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Integration of NMR with Other Open Hole Logs for Improved Porosity, Permeability and Capillary Pressure of Gas Sand Reservoirs

Cited by 4 publications

References 1 publication

Monte Carlo simulation for determining gas saturation using three-detector pulsed neutron logging technology in tight gas reservoir and its application

Monte Carlo simulation for determining gas saturation using three-detector pulsed neutron logging technology in tight gas reservoir and its application

Fluid identification based on geophysical well logs in ultralow-porosity tight sandstone reservoirs

Simulation on the Method of Determining Remaining Oil Saturation by Measuring Dual Pulsed Neutron Parameters

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