Classification and evaluation of low-permeability sand reservoir based on micro-pore structure
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摘要: 针对已有的低渗透储层分类评价方法难以满足北部湾盆地流沙港组低渗透油藏精细评价与油藏开发需求的问题,通过恒速压汞、高压压汞、核磁共振等实验手段开展低渗透储层微观孔隙结构与渗流特征分析,优选储层品质指数、孔隙结构分形维数、主流喉道半径、平均孔喉道半径、可动流体百分数、启动压力梯度变化率共6个参数,基于灰色关联权重分析法建立北部湾盆地低渗透储层综合分类评价标准,进而开展低渗透储量分类评价,为北部湾低渗透储量开发潜力和攻关方向提供依据,分析结果表明:Ⅰ类与Ⅱa类为相对优质的低渗透储量,目前已投入规模开发;Ⅱb类与Ⅲ类为较难动用储量,需采取合理的开发策略与开发模式进行试验性开发;Ⅳ类储量在现有条件下难以有效开发。Abstract: The undeveloped low-permeability oil reserves of the Liushagang Formation in the Beibu Gulf Basin are large, but the reservoir quality is poor. The existing classification standards for low-permeability reservoirs cannot meet the needs of fine reservoir evaluation and offshore development.Based on the experiments of constant rate mercury injection, high pressure mercury injection, NMR and seepage mechanism, this paper comprehensively analyzed the micro-pore structure and seepage characteristics, and optimized six kinds of reservoir evaluation parameters: reservoir quality index, fractal dimension of pore structure, mainstream throat radius, mean throat radius, percentage of movable fluid and change rate of threshold pressure gradient, meanwhile, the classification limit of various characterization parameters were determined by integrating with the reservoir quality index, reservoir seepage ability evaluation factors and specific productivity index constraint parameters. A comprehensive evaluation criterion for low-permeability oil reservoirs is established based on the Grey Relational Analysis method, which is divided into Ⅰ, Ⅱa, Ⅱb, Ⅲ and Ⅳ from good to bad.Carried out the grading evaluation of low-permeability reserves and the research results provide a theoretical basis for the analysis of the development potential, the research direction of the low-permeability reserves in Beibu Gulf Basin.The results show: types Ⅰand Ⅱa are relatively high-quality low-permeability reserves and have been put into large-scale development.Types Ⅱb and Ⅲ are extra-low-permeability reserves and are difficult to develop, which need to be formulated for experimental development by reasonable technical measures and development models.
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图 2 北部湾盆地低渗储层储集空间类型
a.WA-1井,2 650.5 m, 碎屑颗粒以极粗粒占绝对优势,少部分粗粒和砾石;溶蚀强烈,孔隙发育极好,连通性好;b.WA-2井,2 779.8 m,长石基本被溶蚀,形成大量的铸模孔,并生成高岭石等黏土矿物,孔隙发育较好;c.WA-2井,2 774.64 m,长石溶蚀较强烈,部分形成铸模孔、粒内溶孔。整体孔隙较好,连通性一般;d.WA-3井,2 816 m,岩屑粒内溶孔;e.WA-3井,2 867 m,不完全溶蚀,泥质重,部分变质岩受压实作用影响呈假杂基状,孔隙发育较差,连通性差;f.WA-14井,2 900 m,较致密,长石风化较深形成少量黏土化颗粒,部分长石溶蚀形成铸模孔,连通性差;g.WA-7井,2 951 m,颗粒凹凸接触,孔隙不发育,岩石因强烈的压实作用而变得致密;h.WA-8井,2 760 m,铁方解石充填交代,泥质重,孔隙不发育;i.WA-9,井2 614 m,铁方解石胶结,整体孔隙较差,连通性差
Figure 2. Reservoir space types of low-permeability reservoir in Beibu Gulf Basin
表 1 北部湾低渗透储层分类评价标准
Table 1. Classification and evaluation standards of low-permeability reservoirs in Beibu Gulf Basin
储层类型 渗透率/10-3μm2 储层品质指数RQI 孔隙结构分形维
N1储层可动流体品质指数
RQI*SD/%主流喉道半径
Rh/μm平均孔喉道半径
Rkh/μm可动流体饱和度
SD/%启动压力梯度变化率
dP/10-3储层渗流能力评价因子Ip/(10-3μm2·cp-1) 比采油指数/(m3·d-1·MPa-1·m-1) Ⅰ 50~20 >1.1 < 2.15 >60 4~6 >2 >70 >1.12 30~100 >1 Ⅱ Ⅱa
Ⅱb20~10
10~50.9~1.1
0.6 ~0.92.15~2.23 50~60 20~50 3~4
2~3>2 65~70
55~65-3.00~1.12
-19.38~3.0020~30
3~200.5~1
0.2 ~0.5Ⅲ 5~1 0.3~0.6 2.23~2.29 4~20 1~2 1~2 25~55 -114.00~-19.38 0.3~3 0.02~0.2 Ⅳ < 1 < 0.3 >2.29 < 4 < 1 < 1 < 25 < -114 < 0.3 < 0.02 表 2 低渗透储层分类评价参数的权重值
Table 2. Weights of classification parameters for low-permeability reservoirs
评价参数 储层渗流能力评价因子(Ip) 主流喉道半径
(Rh)启动压力梯度变化率
(dP)储层可动流体品质指数(SR) 孔隙结构分形维数(N1) 权重系数 0.272 0.170 0.209 0.210 0.139 -
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