CHARACTERISTICS OF WEATHERED METAMORPHIC ROCKS CRUST IN BOHAI SEA AND ITS QUANTITATIVE PREDICTION
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摘要:
随着渤海油田锦州25-1南、锦州20-2以及渤中26-2等风化壳型油气田的相继发现,以及近两年渤中19-6千亿方大气田的重大勘探突破,元古—太古宇变质岩逐步成为渤海海域潜山勘探层系的重点之一。为了研究渤海变质岩潜山风化壳的发育特征并建立其储层预测方法,通过对典型潜山取心、薄片、测井、常量元素以及物性资料分析,划分了变质岩潜山的风化壳纵向结构,明确了风化壳发育差异的控制因素,并以5项因素灰关联系数为介质,采用Q型聚类法对储层级别进行了优劣排序。研究结果表明:变质岩风化壳可以划分为5个纵向结构,其发育程度明显受岩性、构造和保存条件等因素的影响,其中,被前人忽视的上覆沉积环境作为风化壳的保存条件意义重大。对11口已钻井风化壳进行变量因子归类,由好到差划分了Ⅰ—Ⅳ 4个储层级别。利用该方法在渤中19-6风化壳预测中的应用效果较好。
Abstract:With the discoveries of the oil and gas fields of weathered crust type, such as the Jinzhou 25-1 south, Jinzhou 20-2 and Bozhong 26-2 oilfields, and the breakthrough of the Bozhong 19-6 Gas Field of billions cubic meters in reserve in the past two years, the weathered Proterozoic-Archaean metamorphic rocks have become one of the key exploration targets in the Bohai Sea. In order to reveal the structure of the weathered crust for effective use of the reservoir prediction method to the buried hills consisting of metamorphic rocks, based on coring, thin slices, logging, major elements and physical property data, the vertical structure of the weathered crust of metamorphic buried hill and the controlling factors of weathered crust are studied in this paper. By using the Q-type clustering method and the grey correlation coefficient, the weathered crust of metamorphic rocks can be divided into five vertical sequences, and their development status is obviously affected by lithology, structure and preservation conditions. Among them, the sedimentary environment of the cover, which is often ignored by previous researches, are of great significance as far as the preservation conditions for the weathered crust type of oil and gas fields are considered. According to the variable factor classification for the 11 drilled weathered crusts, four reservoirs fall in classes I-IV from top to bottom. The method has been successfully applied in the prediction of the Bozhong 19-6 weathered crust gas field and should be referred in the future.
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Key words:
- metamorphic rocks /
- weathered crust /
- grey relativity analysis /
- reservoir prediction /
- Bohai Sea
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表 1 渤海主要变质岩类型及其脆性指数
Table 1. Main metamorphic rocks and their brittleness index in Bohai Sea
岩石类型 浅粒质混合岩 混合岩化浅粒岩 浅粒岩 混合花岗岩 混合片麻岩 斜长片麻岩 脆度(β)/% 97.33 95.01 95.00 90.22 84.20~87.63 81.22 表 2 典型井变质岩风化壳厚度与风化时长关系对比
Table 2. Comparison between weathered crust thickness and weathering time for metamorphic rocks
JZ20-A井 JZ25-C井 CFD1-A井 BZ27-A井 BZ26-A井 锆石取样位置 风化时长/×100 Ma 24.89 25.10 25.50 22.99 30.83 风化壳厚度/m 33.90 59.30 50.60 13.60 68.50 表 3 渤海变质岩各井位的控制因素指标均值
Table 3. The mean value of control factors for wells in Bohai Sea
序号 井名 岩石脆度β/% 裂缝/(条/m) 间断时间/(×100 Ma) 古地貌位置* 保存程度** 1 JZ25-A 84.20 4.65 25.11 3 0.393 2 JZ25-B 85.11 4.55 24.82 3 0.316 3 JZ25-C 86.30 4.11 25.10 1 0.433 4 JZ25-D 85.00 2.53 25.24 2 0.357 5 JZ20-A 85.61 3.68 24.89 2 0.306 6 CFD1-A 87.63 1.64 25.50 3 0.325 7 CFD18-B 80.22 1.74 27.93 3 0.309 8 CFD18-A 81.22 1.33 27.55 1 0.211 9 BZ26-A 95.00 5.48 30.83 2 0.287 10 BZ27-A 95.01 2.80 22.99 2 0.277 11 BZ27-B 97.33 3.52 24.87 2 0.286 注:古地貌位置*量化指标为斜坡区风化壳厚度最大,赋值为3,其次为凸起区,赋值为2,低洼区最小,赋值为1;保存程度**量化指标为(1-Ei)/2,其中Ei为水动力指数,与风化壳保存程度呈负相关。 表 4 BZ19-6地区预测与实钻结果对比
Table 4. Comparison of predicted and actual drilled results in BZ19-6 area
A井 B井 C井 D井 预测风化壳类型 Ⅱ类 Ⅰ类 Ⅱ类 Ⅲ类 实钻日产气/万m3 18.0 32.0 8.1 0.1~0.2 实钻日产油/m3 120 310 73 0 吻合程度 优 优 良 良 -
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