The Study On Tight Sandstone Gas Logging Interpretation Of Upper Paleozoic In Yan Qi2–Yan128 Wellblock Of Yan’an Gas Field

Combining with the geologic foundation materials, well-logging data, analytical experiments and production records of Yanqi2-Yan128 wellblock in Yan’an Gas Field, this thesis makes a study on difficulties in identifying lithology of Paleozoic tight sandstone resevoirs, complexity of pore structure and well logging response. Starting from researches on analyzing sedimentation and digenesis of researching area, the main results and understandings can be reached as follows: There developed two types of sedimentary systems, namely the delta sedimentary system(the eighth Member of Xiashihezi Formation, the first and second Member of Shaanxi Formation) and the barrier coast sedimentary system(Benxi Formation). The reservoir lithology is mainly fine sandstone, middle, coarse sandstone, conglomeratic sandstone, coarse sandstone, and sandy conglomerate. The porosity is mainly ranging from 4.0% to 12.0% and 0.01 m D to 3.0m D in permeability, therefore the resevoir belongs to low porosity and low permeability one. Different kinds of diagenesis with complicated diagenetic evolutions developed such as mechanical compaction, pressolution, cementation and dissolution. The average relative error of the computed porosity getting from regression formula which derivates from porosity chart by acoustic time and core analysis porosity after core-normalization does not exceed 7%. It also establishes gas saturation analysis-interpretation model by adopting sealed coring and well logging interpretation. The lower limits of effective thickness and electrical property are made out and tested at last, the thesis considers that the layers which meet the limits can be thought as gas resevoirs and it is consistent with the actual geological conditions.