Abstract
AbstractTight sandstone reservoirs dominated by are developed in the Chang 6 oil layer group of the Yanchang Formation in the central-western part of the Ordos Basin. Featuring the lacustrine delta facies, Chang 6 formation in the center-west area of Ordos Basin shows an increasing petroleum reserve expectation. Its exploitation practice, however, has many problems caused by tight sandstone reservoir features. According to diagenetic and pore analysis, the diagenetic facies in the study area are grouped into four types: chlorite-film-intergranular-pore, feldspar-dissolution, clay-cemented-micropore, carbonate-cemented-tightness for their obvious differences in mineral feature and pore evolution. By introducing the comprehensive classification parameter synthesized from 9 other parameters, the reservoir quality is divided up into four levels: I(Feci > 1), II(3 ≤ Feci ≤ 7), III(-2 ≤ Feci ≤ 3), IV(Feci ≤ -2). The reservoir quality division matches well with the diagenetic facies group. To decide the diagenetic type and reservoir quality division in all wells, the logging data are utilized with the Fisher discriminant method, which has obtained a good performance. The method enables the reservoir quality analysis expanding to all wells from samples, which is helpful for exploitation of the study area.
Highlights
Research ideaDiagenetic facies, one of major factors that shape reservoir quality and pore-throat structure, is a reservoir genetic unit featuring petrophysical and seepage properties (Zou et al 2008)
The Ordos Basin is very rich in tight oil and gas resources and has broad prospects for exploration and development (Yang et al 2013; Guo et al 2017)
The Yanchang Formation develops a set of inland depression-type open lake delta deposits (Fu et al 2005; Wang et al 2006; Li et al 2006; Deng et al 2008)
Summary
Diagenetic facies, one of major factors that shape reservoir quality and pore-throat structure, is a reservoir genetic unit featuring petrophysical and seepage properties (Zou et al 2008). The Ordos Basin is very rich in tight oil and gas resources and has broad prospects for exploration and development (Yang et al 2013; Guo et al 2017) It is the second largest sedimentary basin in China. According to lithology and sedimentary cycle, it can be divided into 10 oil layer groups from top to bottom (Fig. 1): Since the Chang 10th period, the lake basin shape of the early Yanchang Formation has gradually formed. The study area was divided into four diagenetic facies types: residual chlorite-membrane intergranular-pore diagenetic facies, feldspar dissolution diagenetic facies, clay mineral cemented microporous diagenetic facies, carbonate cemented tight diagenetic facies (Table 2). The main diagenesis feature is the development of chlorite membranes on the edges of detrital quartz particles (Fig. 5a), and the intergranular pores are relatively well preserved. The appearance of chlorite film inhibits the increase in quartz in the later period
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