VoL 1 No. 2 Complex Exploration Techniques for the Low-Permeability Lithologic Gas Pool in Ordos Basin 5. Logging gas layer identification and low- impedance gas layer, we effectively identified low-impedance gas layers by comprehensively such methods as array resistivity reversion, time-lapse As far as the tight low-permeability gas layer logging logging, and nuclear magnetic resonance pore structure identification and evaluation are concerned. the main sis. For example, in the He-8 member in the Su-20 methods adopted in our industry can be summed up in well from 3. 439. 4 to 3, 444.4m, the lowest resistivity is the following. The first is the diffusion of high-accuracy 169. m. the highest moveout reaches up to 288us/m, with igital logging and image logging. In all gas exploration good physical properties. But because of its very low well projects we used the CLS3700 instrument, which resistivity and nonnoticeable triangulation response, can map natural gamma ray spectrometer besides routine conventional methods would have been likely to interpret curves. For some wells, we adopted the world-advanced it as a water reservoir. The original layer resistivity Elips-5700 and Maxis-500 image logging series, to obtained through 2D resistivity reversion, is 23.52.m ensure the accuracy of data collection and the need of CMR shows that there are two peaks in the T, spectrum special research. The second is to ensure data accurac of this layer, with well-developed micro pores and by improving the diplex scaling of outdoor instruments generally high porosity, and so low impedance gas and indoor curve standardization. Thirdly, great reservoirs may be formed. On the FMI map, this layer is importance is attached to analyzing and accurately interpreting the logging response mechanism to deep-colored fleck, which shows that the solution pores are well developed. Nuclear magnetic resonance accurately describe the reservoir parameters by core scale interpretation shows a low saturation of free water, and drilling, thick-layer subdivision and classified evaluation. the comprehensive interpretation shows it is a gas Fourthly, on the basis of overall evaluation, we developed bearing member. A combined test of this member and an accurate logging interprettation model based on rock that between 3, 464.2 and 3, 469. 5m shows an open flow physical facies analysis, to draw a general picture from potential of 23 2581 x 10'm'ld(Fig. 6). Finally, focusing perspective of lithologic identification, diagenetic on comprehensive interpretation, we pay much attention rvoir facies analysis and classification of reservo not only to logging information, but also to first-hand ayers and improve the use of logging data. Fifthly, information about corin sample drilling time, gas according to the formation type of the upper Paleozoic logging and so on MI OKSPUP FMI HEQ DYNA 3443 Array lateral resistivity and 2-D reversion CMR nuclear magnetic T2 spectrum FMI resistivity image Fig 6 Log evaluation map of the He-8 low-impedance gas layer Su-20 well o1994-2007chinaAcademicjOurnalElectronicPublishingHouse.Allrightsreservedhttp://www.cnki.netVol.1 No.2 Complex Exploration Techniques for the Low-Permeability Lithologic Gas Pool in Ordos Basin 117 5. Logging gas layer identification and evaluation As far as the tight low-permeability gas layer logging identification and evaluation are concerned, the main methods adopted in our industry can be summed up in the following. The first is the diffusion of high-accuracy digital logging and image logging. In all gas exploration well projects we used the CLS3700 instrument, which can map natural gamma ray spectrometer besides routine curves. For some wells, we adopted the world-advanced Elips-5700 and Maxis-500 image logging series, to ensure the accuracy of data collection and the need of special research. The second is to ensure data accuracy by improving the diplex scaling of outdoor instruments and indoor curve standardization. Thirdly, great importance is attached to analyzing and accurately interpreting the logging response mechanism to accurately describe the reservoir parameters by core scale drilling, thick-layer subdivision and classified evaluation. Fourthly, on the basis of overall evaluation, we developed an accurate logging interprettation model based on rock physical facies analysis, to draw a general picture from the perspective of lithologic identification, diagenetic reservoir facies analysis and classification of reservoir layers and improve the use of logging data. Fifthly, according to the formation type of the upper Paleozoic low- impedance gas layer, we effectively identified some low-impedance gas layers by comprehensively using such methods as array resistivity reversion, time-lapse logging, and nuclear magnetic resonance pore structure analysis. For example, in the He-8 member in the Su-20 well from 3,439.4 to 3,444.4m, the lowest resistivity is 16Ω.m, the highest moveout reaches up to 288μs/m, with good physical properties. But because of its very low resistivity and nonnoticeable triangulation response, conventional methods would have been likely to interpret it as a water reservoir. The original layer resistivity, obtained through 2D resistivity reversion, is 23.5Ω.m. CMR shows that there are two peaks in the T2 spectrum of this layer, with well-developed micro pores and generally high porosity, and so low impedance gas reservoirs may be formed. On the FMI map, this layer is deep-colored fleck, which shows that the solution pores are well developed. Nuclear magnetic resonance interpretation shows a low saturation of free water, and the comprehensive interpretation shows it is a gas￾bearing member. A combined test of this member and that between 3,464.2 and 3,469.5m shows an open flow potential of 23.2581 × 104m 3 /d (Fig. 6). Finally, focusing on comprehensive interpretation, we pay much attention not only to logging information, but also to first-hand information about coring, sample log, drilling time, gas logging and so on. Array lateral resistivity and 2-D reversion CMR nuclear magnetic T2 spectrum FMI resistivity image Fig. 6 Log evaluation map of the He-8 low-impedance gas layer Su-20 well