The Recognition Of Gas Bed In Lower Palaeozoic Era Carbonate Reservoir And The Research On Gas Reservoir Bed Distribution Nature In Yanchang Exploration Area

Yanchang exploration area is located in the southeastern part of the ordos basin. In recent years, there are a few of important gas exploration discoveries in ordovician (Majiagou Fm) reservoir rock, on the paleo-karst slope site.By way of identification between gas and water in lower palaeozoic carbonate reservoir, the major factors of controlling gas bed distribution and the nature of gas distribution are analysyzed, being of important theoretical significance and on the oil and gas exploration.With the well logging, logging, coring, relevant testing material and logging identification as foundation to recognize the gas and water of the lower palaeozoic carbonate rocks.used the resistivity-porosity, water saturation,porosity intersection and double porosity superposed graph, deep lateral resistivity superposed graph and other methods. The main conclusion of the researchis:the conventional identification methods,such as:neutron-density and porosity superposed graph method, the deep the lateral resistivity superposed graph method.etc do an ordinary job in this area, due to the influence of the solution pores and carbonate rock crack, the more influence factors of resistivity; underground complex geological characteristics, the overlapping method is too simplified, intuitive, and can be used as the assistance means for jude gas bed.Resistivity-porosity intersection method, water saturation, porosity intersection method.deep-lower lateral resistivity-porosity intersection method can reduce the interference of crack, solution pores factors to carbonate reservoirs, so they are better on recognizing gas and water. Comparing and testing the interpretation results of using the above three intersection methods with the corrent gas testing results, the recognition rate increased from64.8%to78.8%through comparing the gas testing results of33sections from20Wells. So as to increase the coincidence with recognize the gas and water. The gas identify of exploration areas, according to the intersection methods, has improved the gas recognition rate of single well, and lay a foundation for the distribution laws of gas reservoir research.On the basis of gas reservoirs recognition, to analysis the gas reservoir distribution by use the statistics of the thickness of each layer of a single well, the distribution range of Ma6reservoirs is limited, physical is relative worse, the advantageous area mainly in southeastern of the study area, the main gas reservoirs are in Ma5-1. Ma5-2and Ma5-3, the distribution of gas is scattered, the thickness are different, Ma5-4also has less distribution, gas distribution is decline in one reservoir to another..On the analysis of the main control factors on gasbed distribution nature, discussed the sedimentary environment, the ancient karst landform. weathering, ancient groove distibution cloth, reservoir physical properties, combining macro and micro factors, the main conclusion is:the distribution of gas reservoirs in Zichang-Yanan-Huanglong line the west is better than in the east, the good reservoirs of majiagou group in Yanchang are mainly in middle and upper section of Ma5. Gas bed distribution on the macro is controlled by sedimentary environment, the ancient karst landform, weathering exhibition cloth, groove cutting, on the microscopidlly is restricted by the reservoir property. The ancient groove on both sides has a better gas development, karst dissolving the high slope, karst basin area of the residual high places, main gas reservoirs maintain complete, they are the favorable area for natural gas exploration.