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Method for brittleness index prediction based on grey correlation and analytic hierarchy process:A case study of the tight reservoirs in the Lucaogou Formation of the Jimusaer Sag,Junggar Basin |
LIU Qing1( ), ZHANG Zhen2( ), YANG Shuai1, LI Feng-Ling1 |
1. Oilfield Technology Service Company of Xinjiang Oilfield Company,PetroChina,Karamay 834000,China 2. Karamay Hongshan Oilfield Co.,Ltd. of Xinjiang Oilfield Company,PetroChina,Karamay 834000,China |
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Abstract Owing to the poor physical properties,the tight reservoirs in the Jimusaer Sag can yield industrial oil flow only through hydraulic fracturing.The research on mechanical properties and the brittleness assessment of rocks can provide a certain reference for hydraulic fracturing.This study obtained the mechanical properties of the tight strata in the Jimusaer sag using triaxial mechanical tests and determined the log parameters potentially sensitive to rock brittleness by analyzing the correlation between the sensitivity of the brittleness index and logs.Then,based on the grey correlation theory,this study determined the initial sequence of sensitivity parameters and normalized the parameters selected.Then,it quantitatively correlated the selected parameters with the potential sensitivity to the brittleness index and determined the degrees of correlation and their order.On this basis,this study established a matrix for the pair-wise comparison of the sensitivity parameters using the analytic hierarchy process (AHP) and determined the weight vector.Then,it established the functional relationship model between the brittleness index and the sensitivity parameters,thus developing a new prediction model for the brittleness index.Finally,this study compared the log models with the brittleness model established based on mechanical properties and the brittleness index determined through laboratory tests.The study results are as follows.The tight strata in the Jimusaer Sag have high brittleness,and the comprehensive brittleness index characterized using the whole-process stress-strain curve agreed with the actual brittleness characteristics of rocks.The degree of correlation of the sensitivity parameters determined using the grey correlation method was in the order of natural gamma-ray(GR)>resistivity(Rt)>density(ρ)>neutron(CNL)>sonic interval transit time(ΔT),which had a weight coefficient of 0.33,0.22,0.18,0.16, and 0.11,respectively in the new prediction model.The prediction method proposed in this study was applied to the Lucaogou Formation in the Jimusaer Sag.Compared with that determined through laboratory tests,the brittleness index predicted can reflect the actual brittleness of the formation,exhibiting a high consistency.As shown by the results from well tests,the productivity index of oil was proportional to the brittleness index,and a higher brittleness index was associated a high production capacity after fracturing.Therefore,the new method provides a new approach to brittleness index prediction and guides the parameter selection for the fracturing of reservoirs.
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Received: 20 May 2022
Published: 11 October 2023
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Structural location map of Jimusaer Sag
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Physical property distribution of Lucaogou Formation
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原理分类 | 公式 | 变量说明 | 获取方法 | 基干硬度或坚固性 | BI1= (Hm - H)/K | H为硬度,GPa;Hm为微观硬度,GPa;K为体枳模量,GPa | 硬度测试 | BI2 = H/KIC | KIC为断裂韧性,MPa·m1/2 | 硬度和韧性测试 | BI3 = HE/ | E为静态杨氏模量,GPa | 陶质材料测试 | BI4=qσc | q为直径小于0.6 mm碎屑百分比,%;σc为抗压强度,MPa | 兽氏冲击实絵 | BI5 = c/d | c为裂纹长度,μm;d为韦氏测试特定载荷下贯入尺寸,μm | 贯入实验 | BI6= tdec/tinc | tdec为平均载荷减少时间,s;tinc为平均载荷增加时间,s | BI7 = Fmax/P | Fmax为试件所受最大载荷,kN;P为相应的贯入深度,mm | 基于强度比值 | BI8 = σc/σt | σc为抗压强度,MPa;σt为抗拉强度,MPa | 单轴抗压測试和 巴西劈裂实验 | BI9 = (σc-σt)/(σc+σt) | BI10 = σcσt/2 | BI11 = (σcσt)0.5/2 | 基于全应力—应变特征 | BI12 = (τpτr)/τp | τp为剪切强度峰值,MPa;τr为残余剪切强度,MPa | 应力—应变测试 | BI13 = εr/εt | εr为可恢复应变,无量纲;εt为总应变,无量纲 | BI14= Wr/Wt | Wr为可恢更应变能,J;Wt为总应变能,J | BI15 =εux·100% | εux为不可恢复轴向应变,无量纲 | BI16 = (εp -εr)/εp | εp为应变峰值,无量纲;εr为残余应变,无量纲 | BI17 = π/4 +φ/2 | φ为内摩擦角,rad | 应力应变测试或 声波测井数据 | BI18 = sinφ | 基于弹性力学参数 | BI19 = (En+vn)/2 | En为归一化杨氏模量,无量纲;vn为归一化泊松比,无量纲 | 密度与声波测井 | 基于岩石矿物组分 | BI20 =Wqtz/Wτot BI21 =(Wqtz+Wdot)/Wτot BI22 =(WQFM+WCar)Wτot | Wqtz为石英含量,%;Wτot为矿物总量,% Wdot为白云岩含量,% WQFM为硅酸盐岩含量,%;WCar为脆性碳酸盐岩含量,% | 实验室XRD测试或 矿物含量测井 |
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Statistics of brittleness index evaluation method
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Calculation method of brittleness index based on stress-strain in whole process
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Schematic diagram of brittleness index parameters
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Triaxial stress-strain curves of some rock samples
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编号 | 岩性 | σP/MPa | σr/MPa | εP/% | εr/% | BIP | BIS | BIe | X1 | 泥晶白云岩 | 228.3 | 121.9 | 1.3 | 1.7 | 0.615 | 0.259 | 0.875 | X2 | 泥页岩 | 178.6 | 115.3 | 1.1 | 1.5 | 0.505 | 0.188 | 0.693 | X3 | 砂屑白云岩 | 201.9 | 88.7 | 0.6 | 0.8 | 0.231 | 0.282 | 0.512 | X4 | 白云质粉砂岩 | 162.3 | 89.3 | 0.5 | 0.9 | 0.176 | 0.133 | 0.308 |
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Comprehensive brittleness index of rock samples obtained by experimental method
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Morphology of rock sample after compression
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Cross plot of logging parameters and brittleness index measured in laboratory
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因素 | 自然伽马 GR/API | 电阻率Rt /(Ω·m) | 密度ρ/ (g·cm-3) | 中子CNL/ 0.01 | 声波时差 ΔT/(μs·s-1) | 关联度 | 0.861 | 0.752 | 0.706 | 0.565 | 0.543 | 排序 | 1 | 2 | 3 | 4 | 5 |
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Correlation degree and order of each factor and brittleness index
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标度 | 含义 | 1 | 表示两个因素相比,具有相同的重要性 | 3 | 表示两个因素相比,一个因素比另一个因素稍微重要 | 5 | 表示两个因素相比,一个因素比另一个因素明显重要 | 7 | 表示两个因素相比,一个因素比另一个因素强烈重要 | 9 | 表示两个因素相比,一个因素比另一个因素极端重要 | 2,4,6,8 | 上述两相邻判断重要性的中值 | 倒数 | 因素i与因素j相比,对应aij,则因素j与因素i相比,对应aji=1/aij |
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Comparison matrix scale and its meaning
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元素 | GR/API | Rt/ (Ω·m) | ρ/ (g·cm-3) | CNL/0.01 | ΔT/ (μs·s-1) | GR | 1 | 3 | 3 | 5/3 | 5/3 | Rt | 1/3 | 1 | 3 | 5/3 | 5/3 | ρ | 1/3 | 1/3 | 1 | 35 | /3 | CNL | 3/5 | 3/5 | 1/3 | 1 | 3 | ΔT | 3/5 | 3/5 | 3/5 | 1/3 | 1 |
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Judgment matrix
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n | 指标 | 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 | 10 | IR | 0 | 0 | 0.52 | 0.89 | 1.12 | 1.24 | 1.36 | 1.41 | 1.46 | 1.49 |
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Random consistency values
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Comparison of brittleness index prediction
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Relation between brittleness index and oil production index per meter
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Microseismic monitoring results of hydraulic fracturing
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CHEN Xiu-Juan, LIU Zhi-Di, LIU Yu-Xi, CHAI Hui-Qiang, WANG Yong. Research into the pore structure of tight reservoirs:A review[J]. Geophysical and Geochemical Exploration, 2022, 46(1): 22-31. |
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ZHU Yan, HAN Xiang-Yi, YUE Xin-Xin, YANG Chun-Feng, CHANG Wen-Xin, XING Li-Juan, LIAO Jing. Research and application of brittleness logging evaluation method to tight sandstone reservoirs:Exemplified by Weibei oilfield in Ordos Basin[J]. Geophysical and Geochemical Exploration, 2021, 45(5): 1239-1247. |
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