Abstract
Analyzing the characteristics of rock brittleness in low-permeability mudstone and shale (MS) formations is imperative for efficient hydraulic fracturing stimulation. Rock brittleness depends on the mineral composition, organic matter abundance, and bedding structure. Based on the MS from Shahejie Formation mineral composition (clay mineral, felsic mineral, and calcareous mineral contents), total organic content, and bedding structure (laminated, laminar, and massive), six types of lithofacies were identified: clay-rich MS, felsic-rich MS, calcareous-rich MS, clay MS, felsic MS, and calcareous MS. The quartz, feldspar, calcite, and dolomite of the Shahejie Formation are brittle minerals. Consequently, lithofacies with high felsic and calcareous mineral contents are more brittle. In addition, laminated and laminar MS are also conducive to hydraulic fracturing. Therefore, laminated, organic-rich, and calcareous-rich MS are the dominant lithofacies for hydraulic fracturing in the Shahejie Formation. The lithofacies and brittleness index were predicted by the response characteristics between mineral compositions and logging curves. The 3521–3552 m section of well B11x is dominated by calcareous-rich MS with developed laminae, representing a favorable section for hydraulic fracturing. Fragile minerals and oil are widely developed in the lower part of the lower 1st member of the Shahejie Formation (Es1L) in the southwestern part of Zhaohuangzhuang-Suning, where hydraulic fracturing can be used to increase shale oil production.
Highlights
Abundant continental shale oil resources are the focus of current unconventional oil development and research [1,2,3]
The total organic content (TOC) values of the mudstone and shale (MS) samples ranged from 0.09% to 5.71%, with an average of 1.36%
The S1 value of the 99 samples ranged from 0.01% to 6.27% (Figure 2(b))
Summary
Abundant continental shale oil resources are the focus of current unconventional oil development and research [1,2,3]. The mechanical properties of a continuous distribution are obtained through logging data, including sonic wave and rock density data They define the brittle minerals, which is crucial for calculating the BI using the mineral composition method. Chen et al [38] analyzed the mineral composition, bedding structure, OM abundance, color, and other contaminants in the Dongying Sag and found that the content of mixed fine-grained sedimentary rocks was >60%. Using this definition, the rock was subdivided into 17 lithofacies based on Jiang et al.’s classification scheme [25]. Hydraulic fracturing intervals conducive to shale oil development were selected
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