Early Evaluation Technology About Shallow Gas Reservoir In Continental Facies

On the condition of increasingly shortage of energy resources in our country atpresent and in the future, the resource of shallow gas is an important aspect to solvethis problem, and it also is an important part in oil and gas exploration. Shallow gasusually is the nature gas resource which cover depth is less than 1500m, and it includebiogas, gas separated from oil, coalbed methane, hydrogas etc. Shallow gas resourcesin our country mainly distribute in inshore of Jiangsu and Zhejiang, small southwardMeso-cenozoic bason, eastward petroliferous basin, tsaidamense bason, sichanbason, top formation of some big oilfields and main coal-forming bason. Continentalfacies shallow gas reservoirs have some characteristics, such as the area is small,affecting factor is complex, so which is difficult to identify. These limited theexploitation of this resource. In this article, the author take Heidimiao gas reservoirdescription as an example to put forward a suit of early shallow gas reservoirdescription methods.Through the research, the following results are achieved:1. The whole region are formed by submeridional Putaohua structure belt andnorth-eastward Puxi nose like structure belt. Faults present definite regularity in plane,which formed six fault crowd zones. Cutted by these faults, there are series of traps inthe region of interest. The traps have five types: fault noise, fault anticline, fault block,anticline and dome. The main types are fault noise and fault anticline.2. We discovered that the structure here occured big reverse fore and aft thedeposition of Mingshui formation. Before deposition of Mingshui formation, structureformat is "THREE UPLIFT CLIP TWO SUNKEN", and after deposition of Mingshuiformation, structure format is "ONE UPLIFT". So the palaeostructure summitspossibly are available areas to which gas and oil migrated and assembled. This finding expands the exploitation territory of shallow gas.3. Integrating with the seismic facies analysis results, the log limited sandstoneinversion results and the amplitude sandstone inversion results, the author consideredHeidimiao precipitation facie were a set of anti-cyclicity sandstone and mudstonesediment, which on the structure background of Songliao lake bason shrink steeplyand on the sedimentary background of dispersive proximal little water system. Themain deposit microfacies are underwater distributary channel, split flow mud bay,mouth bar and sand sheet. The single sandstone distribution forms mainly are anmultilayer type and isolation type.4. We used fuzzy identification technique and AVO hydrocarbon indicatortechnique to predict the distribution of nature gas, and discovered that the predicteffect of the two methods was good. The result indicate that the distribution of naturegas is scattered, and the area is small, but the whole reserves is considerable.5. Integrating all results such as nowadays traps, old traps, phases, thickness ofsandstone, result of fuzzy identification and AVO hydrocarbon indicator, weevaluated the advantage areas by using gray correlation analysis technique, andevaluated the advantage traps by using geological holding coefficient technique.Finally, the author bring forward the advantage areas and traps. On the basis ofresearches above, finally the author ascertain well P194-16 as a test well. The tiptopproduction of this well is 91667m~3/d, and the result is inspirer.