珠江口盆地西部文昌B凹陷晚始新-早渐新世复杂储层沉积特征及低渗成因探讨

doi:10.19657/j.geoscience.1000-8527.2019.02.11

摘要/Abstract

摘要：

珠江口盆地西部文昌B凹陷晚始新-早渐新世构造沉积充填演化复杂,受珠三南断裂持续活动影响发育多期次、多点物源的扇三角洲和辫状河三角洲沉积,具有纵向频繁叠置、横向非均质性强的复杂特点。由构造-沉积演化历史研究入手,分析断裂活动时间和差异性对沉积格局、物源注入和储层展布的影响,从而与沉积内幕表现出的复杂性结合来分析垂向相序变化和平面储层展布规律,并开展低渗成因的定量化剖析与探讨,在此基础上对优质储层和有利勘探区带的预测促进了本区油气新发现,也进一步提升了中深层的评价价值。研究得出,文昌B凹陷在文昌组发育两大物源体系,分别形成陡坡带以酸性喷出岩为母岩的扇三角洲和缓坡带以花岗岩为母岩的辫状河三角洲沉积,且后者受母岩类型差异、牵引流为主的沉积机制以及构造挤压应力变弱等因素影响储层物性明显偏好。恩平组纵向上可识别出4期扇三角洲,自下而上呈现多期朵叶体频繁迁移摆动迹象,其中沉积水动力条件和南断裂带差异活动是影响平面储层非均质性的重要因素。因此,在厘定沉积机制和岩相变化为储层物性影响的先决条件这一认识背景下,最终确定以地震相差异与沉积相、岩相的细致对比分析为核心来多角度深入剖析沉积内幕与低渗成因机制应是适合本区中深层的技术体系,并进一步精准预测了“甜点”储层的探寻方向。而在此认识基础上的油气成藏条件再认识,能更成功地指导珠江口盆地西部油气勘探新层系的发现,坚定了文昌B凹陷中深层继续向北拓展勘探的信心。

关键词: 文昌B凹陷, 晚始新-早渐新世, 扇三角洲, 沉积内幕, 低渗成因, “甜点”储层

Abstract:

Late Eocene to Early Oligocene tectonic-sedimentary evolution in the Wenchang B sag (Pearl River estuary basin) is highly complex. Multi-phase and multi-source fan delta deposits and braided delta were formed, which were continuously affected by the Zhu Ⅲ south fault activity. This led to the characteristics of frequent vertical overlays and strong lateral reservoir heterogeneity. By studying the tectonic-sedimentary evolution, we analyzed the effect of fault activity time and mechanism and differences in the sedimentary framework, provenance and reservoir distribution. Combining with the complexity of local sedimentation, we analyzed the vertical facial change and the planar distribution regularity of the reservoir. Based on the sedimentary sequence and facial control, we discussed the genesis of low permeability reservoir and evaluated mid-deep formations. The study shows that there are two provenance systems from the Wenchang B sag, the fan delta that presents mélange deposits of acid extrusive volcanic rock (parent rock) in steep-slope zone, and the braided delta that presents traction current deposits of granite (parent rock) in gentle-slope zone.Physical properties of the latter are clearly better because of the source changes, the traction current mechanism, and the weakly compressive tectonic stress.Besides,there are four phases of fan delta along the sag, whose (from bottom to top) provenance change progressed from east to west.We found that both the sedimentary hydrodynamic conditions and the differential activity of the Zhu Ⅲ south fault are important factors for the planar heterogeneity of the reservoir. In the southern zone (with weak fault activities), the fan delta deposits are featured by their wide sedimentary range, the full handling and elutriation, and the low common shale content, which altogether give better physical properties. Consequently, seismic facies differences and detailed contrast analysis of sedimentary facies and lithofacies can be conducted to study the local sedimentation and low-permeability formation mechanism. This allows better constraint of seismic data and the redefinition of deposition mechanism and phase difference, which can significantly influence reservoir properties. Based on this system, we build on previous knowledge to finely recognize and portrait the scope of distribution and evolution characteristics of the deltaic sedimentary system of each deposition stage, and predict the exploration direction of “sweet point” reservoirs.On the basis of the understanding of hydrocarbon accumulation conditions, we successfully guide the discovery of oil and gas exploration and new horizons in the western Pearl River estuary basin, and increase the confidence of continuously expanding the exploration to the northern zone in the mid-deep formation of the Wenchang B area.

Key words: Wenchang B sag, Late Eocene-Early Oligocene, fan delta, sedimentary insider, mechanism of low permeability, “sweet point” reservoir

中图分类号:

TE121

李珊珊, 彭松, 陈林, 李胜勇, 李连义, 刘小燕. 珠江口盆地西部文昌B凹陷晚始新-早渐新世复杂储层沉积特征及低渗成因探讨[J]. 现代地质, 2019, 33(02): 357-369.

LI Shanshan, PENG Song, CHEN Lin, LI Shengyong, LI Lianyi, LIU Xiaoyan. A Review on the Complex Reservoir Sedimentary Characteristics and Low Permeability Formation of the Upper Eocene to Lower Oligocene in the Wenchang B Sag, Pearl River Estuary Basin[J]. Geoscience, 2019, 33(02): 357-369.

图/表 16

图1 珠江口盆地西部构造区划图

Fig.1 Sketch structural map of the western Pearl River estuary basin

图2 文昌B凹陷构造发育史

Fig.2 Diagram showing the tectonic history of the Wenchang B sag

图3 文昌组矿物组合特征图

Fig.3 Mineral assemblage characteristics of the Wenchang Formation

图4 文昌B凹陷上始新-下渐新统储层展布特征连井对比图

Fig.4 Comparison diagram of the Late Eocene to Early Oligocene reservoir distribution characteristics,Wenchang B sag

图5 文昌B凹陷典型地震相识别特征(剖面位置已标识在图6平面图中)

Fig.5 Discriminating features of typical seismic facies in the Wenchang B sag

图6 恩平组多期次扇三角洲平面展布图

Fig.6 Planar distribution map of the multi-stages delta in the Enping Formation

图7 储层物性与岩石组分、填隙物含量、粒径、砂岩厚度相关性分析图

Fig.7 Correlation analysis diagram for the components, interstitial material, median grain size and sandstone thickness, and the reservoir physical properties

图7 储层物性与岩石组分、填隙物含量、粒径、砂岩厚度相关性分析图

Fig.7 Correlation analysis diagram for the components, interstitial material, median grain size and sandstone thickness, and the reservoir physical properties

图8 文昌组储层特征岩心照片与显微照片

Fig.8 Core photos and microphotos of the reservoir characteristics from the Wenchang Formation

图8 文昌组储层特征岩心照片与显微照片

Fig.8 Core photos and microphotos of the reservoir characteristics from the Wenchang Formation

表1 恩平组储层物性影响因子多元线性回归分析表

Table 1 Multiple linear regression of the impact factor of the reservoir properties in the Enping Formation

因素	系数	标准误差	tStat	P-value	标准系数	权重/%
const	31.154	23.679	1.316	0.193 841	12.923	/
H'(埋深)	-2.215	2.940	-0.754	0.454 331	-3.323	11
h'(厚度)	1.287	0.335	3.842	0.000 323	8.521	28
Q(石英)	0.015	0.029	0.522	0.603 728	1.143	4
F(长石)	-0.115	0.105	-1.096	0.278 073	-2.651	9
V_sh(泥质)	-0.197	0.071	-2.799	0.007 092	-5.921	20
C(胶结物)	-0.455	0.148	-3.073	0.003 321	-3.637	12
s(分选性)	0.059	0.042	1.408	0.164 865	4.757	16

表1 恩平组储层物性影响因子多元线性回归分析表

Table 1 Multiple linear regression of the impact factor of the reservoir properties in the Enping Formation

因素	系数	标准误差	tStat	P-value	标准系数	权重/%
const	31.154	23.679	1.316	0.193 841	12.923	/
H'(埋深)	-2.215	2.940	-0.754	0.454 331	-3.323	11
h'(厚度)	1.287	0.335	3.842	0.000 323	8.521	28
Q(石英)	0.015	0.029	0.522	0.603 728	1.143	4
F(长石)	-0.115	0.105	-1.096	0.278 073	-2.651	9
V_sh(泥质)	-0.197	0.071	-2.799	0.007 092	-5.921	20
C(胶结物)	-0.455	0.148	-3.073	0.003 321	-3.637	12
s(分选性)	0.059	0.042	1.408	0.164 865	4.757	16

图9 文昌B凹陷地震相与岩相组合、物性的对应关系

Fig.9 Corresponding relations between seismic facies, lithofacies assemblage and physical properties in the Wenchang B sag

图9 文昌B凹陷地震相与岩相组合、物性的对应关系

Fig.9 Corresponding relations between seismic facies, lithofacies assemblage and physical properties in the Wenchang B sag

表2 文昌B凹陷恩平组地震相与岩相组合、储层发育特征统计分类表

Table 2 Statistics of the seismic facies, lithofacies assemblage, and reservoir development features in the Wenchang B sag

井名	恩平组一段							恩平组二段
井名	地震相	岩相组合	砂地比/%	有效储层比例/%	孔隙度/%	泥质含量/%		地震相	岩相组合	砂地比/%	有效储层比例/%	孔隙度/%	泥质含量/%
2井	弱振幅、杂乱地震相	富砂岩相段,砂岩单层厚度大,泥质含量低,物性好	54	87.20	21.30	3.3~14.3	弱振幅、杂乱地震相		富砂岩相段,砂岩单层厚度大,泥质含量低,物性好	64	72.20	16.50	2~14.8
M1井	弱振幅、杂乱地震相	富砂岩相段,砂岩单层厚度大,泥质含量低,物性好	66	87.80	18.70	3~15	弱振幅、杂乱地震相		富砂岩相段,砂岩单层厚度大,泥质含量低,物性好	52	72.80	13.90	2~12
1井	中振幅、亚平行地震相	上段为厚层砂岩、泥质砂岩,下段砂泥岩互层,泥质含量高	78	74	16.80	6~18	中振幅、亚平行地震相		砂泥岩混杂堆集,单层厚度薄,物性差	46	0 (干层)	9	11~19
N1井	弱振幅、杂乱地震相	富砂岩相段,单层厚度大,物性好	未钻穿, 不参与统计	70	17.50	1.9~11.2	弱振幅、杂乱地震相		预测为富砂岩相段,单层厚度大,物性好

表2 文昌B凹陷恩平组地震相与岩相组合、储层发育特征统计分类表

Table 2 Statistics of the seismic facies, lithofacies assemblage, and reservoir development features in the Wenchang B sag

井名	恩平组一段							恩平组二段
井名	地震相	岩相组合	砂地比/%	有效储层比例/%	孔隙度/%	泥质含量/%		地震相	岩相组合	砂地比/%	有效储层比例/%	孔隙度/%	泥质含量/%
2井	弱振幅、杂乱地震相	富砂岩相段,砂岩单层厚度大,泥质含量低,物性好	54	87.20	21.30	3.3~14.3	弱振幅、杂乱地震相		富砂岩相段,砂岩单层厚度大,泥质含量低,物性好	64	72.20	16.50	2~14.8
M1井	弱振幅、杂乱地震相	富砂岩相段,砂岩单层厚度大,泥质含量低,物性好	66	87.80	18.70	3~15	弱振幅、杂乱地震相		富砂岩相段,砂岩单层厚度大,泥质含量低,物性好	52	72.80	13.90	2~12
1井	中振幅、亚平行地震相	上段为厚层砂岩、泥质砂岩,下段砂泥岩互层,泥质含量高	78	74	16.80	6~18	中振幅、亚平行地震相		砂泥岩混杂堆集,单层厚度薄,物性差	46	0 (干层)	9	11~19
N1井	弱振幅、杂乱地震相	富砂岩相段,单层厚度大,物性好	未钻穿, 不参与统计	70	17.50	1.9~11.2	弱振幅、杂乱地震相		预测为富砂岩相段,单层厚度大,物性好

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