The Reservoir Characteristics And Heterogeneity Study Of Yanchang Formation In ZL Oilfield

ZL oilfield locates in the Ordos basin eastern slope zone which is a gentle western-leaning monoclinic. It is a typical low porosity and low permeability reservoir, with the characteristics of large vertical distribution span, various strata, much difference type,strong heterogeneity, and various reservoir types. Reservoir internal heterogeneity had a great influence on pore fluid and oil recovery. For searching for the better development programs and choosing an effective method of expulsion and completion methods, it is necessary to do research work on reservoir heterogeneity which could provide more accurate parameters for the residual oil distribution, and have an important guiding for the next step exploration prediction and oil recovery enhancement of oil-bearing layers in new area.Based on the drilling, mud logging, core, laboratory analysis and other geological data,combining with the well logging data, stratigraphy of Chang2 and Chang6 in ZL oilfield are detailedly divided and correlated. Yanchang formation characteristics have been analyzed from the petrologic features including rock types, lithology, porosity structure, physical property and sensitivity. Using reservoir permeability parameters, interlayers, bay level,stratification coefficient, the in-layer, interlayer and plane reservoir heterogeneity of Chang2 and Chang6 have been studied, and the heterogeneity feature comparison of different oil-bearing layer is done.The results show that, Chang2 reservoir in ZL oilfield is divided into three small layers of Chang2¹, 2², 2³; Chang6 reservoir is divided into four small layers of Chang6¹, 6², 6³, 6⁴.Chang2 reservoir belong to a low porosity and low permeability reservoir, and its pore type is mainly intergranular pore with average pore diameter of 58?m, average porosity of 12.8% and average permeability of 1.85×10^-3?m². Chang6 reservoir belong to ultra-low permeability reservoirs, and its pore type is also mainly intergranular pore with average pore diameter of62.66?m, average porosity of 10.3% and average permeability of 0.72×10^-3?m². The in-layer heterogeneity of Chang2 reservoir is stronger than Chang6. Chang2 is given priority topositive rhythm and mud interlayer. The interlayer heterogeneity of Chang6 reservoir is stronger than Chang2,and Chang6 has a large stratification coefficient and is given priority to positive rhythm and mud interlayer. The plane heterogeneity of Chang2 reservoir is stronger than Chang6, Chang2 reservoir sand drill encounter rate is about 83.5%, Chang6 reservoir is about 84.3% in sand drill encounter rate, Chang6 has a good plane connectivity, but the permeability distribution in plane is in a large range.