Reservoir connectivity of offshore oilfields with a sparse well pattern: a case study of the third member of Weizhou Formation of oilfield A in Weixinan Sag, Beibuwan Basin
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摘要: 为解决北部湾盆地涠西南凹陷A油田涠三段注采矛盾突出、剩余油分布复杂且难以动用等问题,通过储层构型界面分级、复合砂体解剖、储层构型单元定量化表征等海上稀疏井网油田储层构型技术体系开展研究,指导A油田储层连通性分析,从而解决A油田涠三段生产难题。垂向上,A油田涠三段不同油组可划分为3~4期单成因砂体;侧向上,综合储层侧向接触模式、砂体侧向规模约束、井震结合研究、生产动态验证,得到不同注采井在同期砂体的储层构型剖面;结合不同油组的沉积微相变化及水下分流河道厚度与宽度之间存在着正相关关系,进一步对A油田涠三段储层构型单元进行了定量化表征。在此基础上,从剖面和平面上分别对A油田主力开发层系W3ⅣD、W3ⅣE油组的连通性进行分析。剖面上,W3ⅣD油组水下分流河道砂体垂向叠置,河道间砂体连续性中等,横向整体连通性较好;平面上,南西物源方向的河道微摆动,规模变化较大,局部发育小规模河口坝,北东物源方向的河道较为顺直,规模变化不大。剖面上,W3ⅣE油组北部单井垂向上沉积微相及井间砂体厚度变化较快,砂体连续性一般,南部整体呈弱连通状态;平面上,南西物源方向的河道摆动明显,河口坝较发育,北东物源方向的河道较为顺直,间湾较发育。Abstract: To address the prominent injection and production contradiction, complex remaining oil distribution, and utilization issues in the third member of the Weizhou Formation (W3) of oilfield A in the Weixinan Sag, Beibuwan Basin, the study developed a comprehensive reservoir configuration characterization system for offshore oilfields with a sparse well pattern, involving reservoir configuration interface classification, anatomy of composite sand body, and quantitative characterization of reservoir configuration unit. The reservoir connectivity was studied, aiming to optimize production strategies in the area. Vertically, the different oil groups in the third member of the Weizhou Formation in oilfield A could be divided into 3 to 4 monogenetic sand bodies. For lateral characterization, the study integrated multiple approaches, including reservoir contact pattern analysis, sand body scale constraints, well and seismic combination, and dynamic verification of production data to obtain the reservoir configuration profiles of different injection and production wells in the same period. Combined with variations in sedimentary microfacies of different oil groups and the positive correlations between the thickness and width of subaqueous distributary channels, the reservoir configuration unit of the third member of the Weizhou Formation in oilfield A was further quantitatively characterized. Based on that, the lateral and vertical connectivity of W3ⅣD and W3ⅣE oil groups in the main development layers of oilfield A was analyzed. Profile characterization of the W3ⅣD oil group showed that the subaqueous distributary channel sand bodies were vertically superimposed with moderate inter-channel sand body continuity and overall good lateral connectivity. Planar analysis showed that the river channels in the southwest provenance direction swung slightly with significant scale variations. Small-scale mouth bars were locally developed. The river channels in the northeast provenance direction were relatively straight with few scale variations. For W3ⅣE oil groups, the northern wells showed rapid changes in vertical sedimentary microfacies of single well and sand body thickness between wells, with moderate sand body continuity. The southern wells generally exhibited weaker connectivity. Planar studies revealed evident swings of river channels in the southwest provenance direction and well-developed mouth bars. The river channels in the northeast provenance direction were relatively straight, and the interdistributary bays were more developed.
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表 1 碎屑沉积地质体构型界面分级据参考文献[20-21]修改。
Table 1. Classification of configuration interfaces for clastic sedimentary geological body
构型界面级别 时间规模/a 构型单元(以河流相为例) 米兰科维奇旋回 MIALL界面分级 经典层序地层分级 基准面旋回分级 油层对比单元分级 1级 108 叠合盆地充填复合体 巨层序 2级 107~108 盆地充填复合体 超层序 3级 106~107 盆地充填体 8 层序 长期 含油层系 4级 105~106 体系域 偏心率周期 7 准层序组 中期 油层组 5级 104~105 叠置河流沉积体 黄赤交角周期 6 准层序 短期 砂组/小层 6级 103~104 曲流带/辫状带 岁差周期 6 层组 超短期 单层 7级 103~104 河流沉积体 5 层 8级 102~103 点坝/心滩坝 4 层 9级 100~101 增生体 3 层 10级 10-2~10-1 层系组 2 纹层组 11级 10-3~10-5 层系 1 纹层组 12级 10-6 纹层 0 纹层 表 2 北部湾盆地涠西南凹陷A油田辫状河三角洲储层构型分级方案
Table 2. Configuration classification scheme for braided river delta reservoirs in oilfield A of Weixinan Sag, Beibuwan Basin
构型界面级别 时间规模/a 构型单元 储集层构型要素 MIALL界面分级[20] 经典层序地层分级 基准面旋回分级 6级 103~104 三角洲沉积体 分流河道砂层组顶、底界面 6 层组 超短期 7级 103~104 同期水下分流河道和河口坝复合体 分流河道砂体顶、底界面 5 层 8级 102~103 单一水下分流河道或河口坝 分流河道砂体侧积体顶面 4 层 9级 100~101 内部增生体 洪水期不同阶段沉积界面 3 层 10级 10-2~10-1 层系组 交错层系组界面 2 纹层组 11级 10-5~10-3 层系 交错层系界面 1 纹层组 12级 10-6 纹层 纹层 0 纹层 表 3 北部湾盆地涠西南凹陷A油田及围区水下分流河道展布定量规模数据
Table 3. Quantitative scale data of subaqueous distributary channels in oilfield A and its surronding area, Weixinan Sag, Beibuwan Basin
油组 前缘分支河道数 河道期次 复合河道厚度/m 复合河道宽度/m 复合河道宽厚比 单一河道厚度/m 单一河道宽度/m 单一河道宽厚比 定量关系 W3Ⅰ 6~7 3 10.9~21.3 459~697 33~46 2.0~10.8 201~697 51~88 W=127.86H0.710 5 R2=0.744 5 W3ⅣD 5~6 3 9.1~30.0 417~912 27~58 2.2~13.7 239~912 58~88 W=136.99H0.697 9 R2=0.740 8 W3ⅣE 4~6 4 10.1~25.8 440~751 26~53 2.3~10.7 270~751 63~90 W=159.55H0.652 1 R2=0.676 7 W3Ⅴ 6 3 6.3~16.9 407~671 35~62 2.0~8.2 261~655 66~92 W=126.27H0.752 5 R2=0.557 7 W3Ⅵ 6 3 6.4~18.2 344~872 30~68 2.1~10.9 309~872 61~89 W=76.953H1.010 9 R2=0.782 0 W3Ⅶ 5~6 4 7.2~24.0 362~783 25~53 2.4~11.4 236~783 58~90 W=119.42H0.779 4 R2=0.769 6 W3Ⅷ 5~6 3 7.9~26.1 380~846 31~61 2.6~14.3 265~846 56~88 W=161.52H0.625 3 R2=0.681 1 W3Ⅸ 6 4 10.7~25.0 398~834 24~58 2.0~11.0 212~767 56~89 W=130.23H0.726 5 R2=0.770 6 W3Ⅹ 3~6 3 6.6~17.5 368~777 36~58 2.5~11.1 298~734 63~92 W=171.83H0.607 4 R2=0.693 3 W3Ⅺ 6 3 8.0~20.3 435~801 32~55 3.3~13.4 344~801 51~90 W=171.83H0.607 4 R2=0.693 3 -
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