The influence of major faults and fractures on the development of non-matrix porosity system in a pre-salt carbonate reservoir, Santos Basin – Brazil

IF 2.6 2区 地球科学 Q2 GEOSCIENCES, MULTIDISCIPLINARY Journal of Structural Geology Pub Date : 2024-10-12 DOI:10.1016/j.jsg.2024.105271
Luiza de C. Mendes , Mateus Basso , Juan Villacreces Morales , Guilherme F. Chinelatto , Joan Marie Blanco , Ulisses M.C. Correia , João Paulo Ponte , Gabriela F. Matheus , Marilia M. Camargo , Jean Carlos R. Gavidia , Renato S.P.de Medeiros , Alexandre C. Vidal
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Abstract

Faults and fractures are central for characterizing the permeability distribution in carbonate reservoirs since they act as pathways for diagenetic fluids that often favor intense rock dissolution and permeability. Usually, high permeability zones and fractures are not easily recognized in seismic data due to limited resolution and they are often associated with higher concentrations of hydrocarbons or even significant fluid losses during drilling, thus creating a challenge for hydrocarbon exploration. In the Santos Basin, southeast Brazil, the pre-salt carbonate reservoirs from the Barra Velha Formation (BVE) are the main hydrocarbon producers in Brazilian Atlantic margin and well-known for being extremely heterogeneous, exhibiting complex dual-porosity systems. In this study, we built a conceptual model of these fracture zones and non-matrix porosity formation that helped narrowing the understanding of these complex systems. The characterization of faults and fractures was carried out using seismic, well-logs, and borehole image data to understand the influence of these structures in the porosity formation along the Barra Velha Formation. In the study area, three fault sets were defined (F1, F2, and F3) from seismic data. F1 represents to the larger faults, while the F3 fault set represents the smaller faults related to the reactivation of F1; both sets being oriented NE-SW. The F2 fault set is associated with the rift formation and is oriented to NNE-SSW. These three fault sets compartmentalized the studied area into different domains, each exhibiting distinct fracture sets. The natural open fractures were formed during the reactivation of rift faults and are oriented mainly NW, NNE-NNW, NE, and ENE and were identified across the entire study area, but with different intensity values. The fracture intensity closely relates to the distance from major faults where the wells with the highest fracture intensity occurs located 150–590 m from the larger F1 fault set. Scan-lines were conducted throughout the area to determine the fault width, and an average value of 1.2 km was established. Seven non-matrix porosity classes were characterized and classified into stratigraphically concordant and discordant non-matrix pore types at well scale through borehole image interpretation. The Barra Velha Formation exhibit higher occurrence of stratigraphically discordant non-matrix porosity related to fractured zones while stratigraphically concordant non-matrix porosity is mainly controlled by the paleotopography of the study area. Overall, non-matrix porosity formation tends to follow an orientation that suggests a preferential dissolution flow towards NE and ENE directions. Intervals with higher silica content shows a positive correlation with both fracture intensity and stratigraphically discordant non-matrix porosities. This work provides a conceptual model about the fractures and non-matrix porosity distribution in pre-salt carbonate rocks that can help address some of associated structural and stratigraphic uncertainties during field appraisal and development.
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主要断层和裂缝对巴西桑托斯盆地盐前碳酸盐岩储层非矩阵孔隙度系统发展的影响
断层和裂缝是描述碳酸盐岩储层渗透率分布特征的核心,因为它们是成岩流体的通道,往往有利于岩石的强烈溶解和渗透。通常,由于分辨率有限,地震数据不易识别高渗透带和断裂,而且它们往往与较高的碳氢化合物浓度或钻探过程中的大量流体损失相关联,从而给碳氢化合物勘探带来了挑战。在巴西东南部的桑托斯盆地,来自 Barra Velha Formation(BVE)的盐前碳酸盐岩储层是巴西大西洋边缘的主要碳氢化合物产地,因其异质性极强、表现出复杂的双孔隙度系统而闻名。在这项研究中,我们建立了这些断裂带和非基质孔隙度形成的概念模型,有助于加深对这些复杂系统的理解。我们利用地震、井录和井眼图像数据对断层和裂缝进行了特征描述,以了解这些结构对 Barra Velha 地层沿线孔隙度形成的影响。在研究区域,根据地震数据确定了三个断层组(F1、F2 和 F3)。F1 代表较大的断层,而 F3 断层组则代表与 F1 重新激活有关的较小断层;两组断层均呈东北-西南走向。F2 断层组与裂谷地层有关,走向为东北-西南。这三个断层组将研究区域划分为不同的区域,每个区域都有不同的断裂组。天然开放断裂是在裂谷断层重新活化过程中形成的,主要走向为 NW、NNE-NNW、NE 和 ENE。断裂强度与主要断层的距离密切相关,断裂强度最高的水井位于距离较大的 F1 断层组 150-590 米处。为确定断层宽度,在整个区域内进行了扫描测线,确定平均值为 1.2 千米。通过井眼图像解释,在油井尺度上确定了七个非基质孔隙度等级,并将其划分为地层一致和不一致的非基质孔隙类型。Barra Velha 地层的地层不和谐非基质孔隙度较高,与断裂带有关,而地层和谐非基质孔隙度主要受研究区域的古地形控制。总体而言,非基质孔隙度的形成方向倾向于向东北和东北方向溶解流动。二氧化硅含量较高的区段与断裂强度和地层不和谐的非基质孔隙度均呈正相关。这项研究为盐前碳酸盐岩中的裂缝和非基质孔隙度分布提供了一个概念模型,有助于解决油田评价和开发过程中一些相关的构造和地层不确定性问题。
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来源期刊
Journal of Structural Geology
Journal of Structural Geology 地学-地球科学综合
CiteScore
6.00
自引率
19.40%
发文量
192
审稿时长
15.7 weeks
期刊介绍: The Journal of Structural Geology publishes process-oriented investigations about structural geology using appropriate combinations of analog and digital field data, seismic reflection data, satellite-derived data, geometric analysis, kinematic analysis, laboratory experiments, computer visualizations, and analogue or numerical modelling on all scales. Contributions are encouraged to draw perspectives from rheology, rock mechanics, geophysics,metamorphism, sedimentology, petroleum geology, economic geology, geodynamics, planetary geology, tectonics and neotectonics to provide a more powerful understanding of deformation processes and systems. Given the visual nature of the discipline, supplementary materials that portray the data and analysis in 3-D or quasi 3-D manners, including the use of videos, and/or graphical abstracts can significantly strengthen the impact of contributions.
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