Evaluation method for low to ultralow permeability reservoirs based on pore-throat structure: A case study in the eastern Nanpu Sag, Bohai Bay Basin, China

2020 ◽  
pp. 1-47
Author(s):  
Xiaodong Zhao ◽  
Shilin Wang ◽  
Jingxu Yang ◽  
Boming Zhang ◽  
Liang Li ◽  
...  
Keyword(s):  
Physical Properties ◽  
Evaluation Method ◽  
Maximum Pressure ◽  
Bohai Bay ◽  
Pore Throat ◽  
Bohai Bay Basin ◽  
Throat Radius ◽  
Thin Sections ◽  
Nanpu Sag ◽  
Ultralow Permeability

The pore-throat structure of low to ultralow permeability reservoirs is complex, causing the permeability to vary greatly under similar porosity conditions. And the pore-throat structures are the key factors that controlled the physical properties of such kind of reservoirs. Therefore, conventional reservoir evaluation methods can hardly meet the research needs of low to ultralow permeability reservoir exploration and development. We conducted our research on Paleogene Shahejie and Neogene Dongying low to ultralow permeability reservoirs in the eastern Nanpu Sag of the Bohai Bay Basin in order to address this issue. Cores, thin sections and scanning electron microscope were used to analyze the pore-throat structures in order to determine the characteristics of low to ultralow permeability reservoirs and a new parameter for evaluating low to ultralow permeability reservoirs is proposed. The results of this research show that primary pores, secondary pores and micro-fractures are developed in the study area, and the pore-throat shape is mainly flaky or curved flaky. The microscopic pore-throat structure controlled the reservoir physical properties and fluid mobility of these reservoirs, the permeabilities of these reservoirs are dependent on the pore throats, and the correlation between connected pores and permeability is strong. Based on the analysis of the pore-throat structure, as well as the maximum mercury saturation and the residual mercury saturation at the maximum pressure and the minimum pressure obtained by the mercury injection test, an evaluation of the reservoir by using the mobility parameter of fluid is proposed, and the pore-throat radius R15 obtained by the mercury intrusion experiment has the best correlation with the fluid mobility parameters. The mobility parameters of fluid can effectively improve the accuracy of logging interpretation of low to ultralow permeability reservoirs and provide a scientific basis for the scale stimulation and effective development of low to ultralow permeability reservoirs.

scholarly journals The influences of sedimentary environments on organic matter enrichment in fine-grained rocks of the Paleogene Shahejie formation in Nanpu Sag, Huanghua Depression, Bohai Bay Basin

2021 ◽  
pp. 014459872110310
Author(s):  
Min Li ◽  
Xiongqi Pang ◽  
Guoyong Liu ◽  
Di Chen ◽  
Lingjian Meng ◽  
...  
Keyword(s):  
Organic Matter ◽  
Source Rocks ◽  
Bohai Bay ◽  
Bohai Bay Basin ◽  
Humid Climate ◽  
High Productivity ◽  
Fine Grained ◽  
Huanghua Depression ◽  
Shahejie Formation ◽  
Nanpu Sag

The fine-grained rocks in the Paleogene Shahejie Formation in Nanpu Sag, Huanghua Depression, Bohai Bay Basin, are extremely important source rocks. These Paleogene rocks are mainly subdivided into organic-rich black shale and gray mudstone. The average total organic carbon contents of the shale and mudstone are 11.5 wt.% and 8.4 wt.%, respectively. The average hydrocarbon (HC)-generating potentials (which is equal to the sum of free hydrocarbons (S1) and potential hydrocarbons (S2)) of the shale and mudstone are 39.3 mg HC/g rock and 28.5 mg HC/g rock, respectively, with mean vitrinite reflectance values of 0.82% and 0.81%, respectively. The higher abundance of organic matter in the shale than in the mudstone is due mainly to paleoenvironmental differences. The chemical index of alteration values and Na/Al ratios reveal a warm and humid climate during shale deposition and a cold and dry climate during mudstone deposition. The biologically derived Ba and Ba/Al ratios indicate high productivity in both the shale and mudstone, with relatively low productivity in the shale. The shale formed in fresh to brackish water, whereas the mudstone was deposited in fresh water, with the former having a higher salinity. Compared with the shale, the mudstone underwent higher detrital input, exhibiting higher Si/Al and Ti/Al ratios. Shale deposition was more dysoxic than mudstone deposition. The organic matter enrichment of the shale sediments was controlled mainly by reducing conditions followed by moderate-to-high productivity, which was promoted by a warm and humid climate and salinity stratification. The organic matter enrichment of the mudstone was less than that of the shale and was controlled by relatively oxic conditions.

scholarly journals Microscale Pore Throat Differentiation and Its Influence on the Distribution of Movable Fluid in Tight Sandstone Reservoirs

Geofluids ◽  
2021 ◽  
Vol 2021 ◽  
pp. 1-7
Author(s):  
Fengjuan Dong ◽  
Xuefei Lu ◽  
Yuan Cao ◽  
Xinjiu Rao ◽  
Zeyong Sun
Keyword(s):  
Ordos Basin ◽  
Pore Throat ◽  
Tight Sandstone ◽  
Throat Radius ◽  
Thin Sections ◽  
Small Pore ◽  
Sandstone Reservoir ◽  
Sandstone Reservoirs ◽  
Classification Evaluation ◽  
Better Than

Tight sandstone reservoirs have small pore throat sizes and complex pore structures. Taking the Chang 6 tight sandstone reservoir in the Huaqing area of the Ordos Basin as an example, based on casting thin sections, nuclear magnetic resonance experiments, and modal analysis of pore size distribution characteristics, the Chang 6 tight sandstone reservoir in the study area can be divided into two types: wide bimodal mode reservoirs and asymmetric bimodal mode reservoirs. Based on the information entropy theory, the concept of “the entropy of microscale pore throats” is proposed to characterize the microscale pore throat differentiation of different reservoirs, and its influence on the distribution of movable fluid is discussed. There were significant differences in the entropy of the pore throat radius at different scales, which were mainly shown as follows: the entropy of the pore throat radius of 0.01~0.1 μm, >0.1 μm, and <0.01 μm decreased successively; that is, the complexity of the pore throat structure decreased successively. The correlation between the number of movable fluid occurrences on different scales of pore throats and the entropy of microscale pore throats in different reservoirs is also different, which is mainly shown as follows: in the intervals of >0.1 μm and 0.01~0.1 μm, the positive correlation between the occurrence quantity of movable fluid in the wide bimodal mode reservoir is better than that in the asymmetric bimodal mode reservoir. However, there was a negative correlation between the entropy of the pore throat radius and the number of fluid occurrences in the two types of reservoirs in the pore throat radius of <0.01 μm. Therefore, pore throats of >0.1 μm and 0.01~0.1 μm play a controlling role in studying the complexity of the microscopic pore throat structure and the distribution of movable fluid in the Chang 6 tight sandstone reservoir. The above results deepen the understanding of the pore throat structure of tight sandstone reservoirs and present guiding significance for classification evaluation, quantitative characterization, and efficient development of tight sandstone reservoirs.

Intense faulting and downwarping of Nanpu Sag in the Bohai Bay Basin, eastern China: Response to the Cenozoic Stagnant Pacific Slab

2019 ◽  
Vol 109 ◽  
pp. 819-838 ◽  
Author(s):  
Rui Zhao ◽  
Si Chen ◽  
Hua Wang ◽  
Huajun Gan ◽  
Guanhong Wang ◽  
...  
Keyword(s):  
Eastern China ◽  
Bohai Bay ◽  
Bohai Bay Basin ◽  
Pacific Slab ◽  
Nanpu Sag

A double-cycle lake basin formed in extensional to transtensional setting: The Paleogene Nanpu Sag, Bohai Bay Basin, China

2017 ◽  
Vol 349 ◽  
pp. 15-32 ◽  
Author(s):  
Jianguo Zhang ◽  
Zaixing Jiang ◽  
Elizabeth Gierlowski-Kordesch ◽  
Benzhong Xian ◽  
Zhenpeng Li ◽  
...  
Keyword(s):  
Lake Basin ◽  
Bohai Bay ◽  
Bohai Bay Basin ◽  
Nanpu Sag

The Law of Reservoir Property Change both before and after Water Flooding in Liaohe Oilfield

2015 ◽  
Vol 733 ◽  
pp. 31-34
Author(s):  
Yan Zhang ◽  
Shuang Yu
Keyword(s):  
Physical Properties ◽  
Water Flooding ◽  
Pore Throat ◽  
Reservoir Properties ◽  
Throat Radius ◽  
Liaohe Oilfield ◽  
Before And After ◽  
Mouth Bar ◽  
Oilfield Development ◽  
Distributary Channel

In order to explore the change laws of physical properties and pore throat radius of reservoir both before and after water flooding to guide the oilfield in-depth fluid diversion, the reservoir properties are analyzed on the basis of core data of early exploratory well and inspection well in the middle and later stages of oilfield development. The theory of reservoir geology and development geology is used to study the change laws of reservoir properties both before and after water flooding in May 20th Development Area of Liaohe oilfield. The research result indicates that reservoir physical properties and pore throat radius have changed in the different period and different microfacies types of sand body [1-3].The permeability is changed far outweigh porosity in the physical properties of reservoir. And with the increase of time, the biggest change is the porosity and permeability of distributary channel, the next are margin of channels, mouth bar. The thin layer of channels and distal bar of physical properties have changed lesser or not. The pore throat radius has declined following distributary channel, mouth bar, thin layer of channels and distal bar in the sedimentary microfacies [4-5].The study results are helpful for the establishment of production measures at the later stage of oilfield development.

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