scholarly journals Seepage Behavior of Fractures in Paleogene Sandstone Reservoirs in Nanpu Sag, Bohai Bay Basin, Eastern China

2021 ◽  
Vol 9 ◽  
Author(s):  
Zhaosheng Wang ◽  
Meiri Muhtar ◽  
Donghao Xu ◽  
Jinchuan Fang ◽  
Jing Li ◽  
...  
Keyword(s):  
Fractured Reservoirs ◽  
Stress Sensitivity ◽  
Formation Mechanisms ◽  
Fracture Aperture ◽  
Bohai Bay ◽  
Natural Fractures ◽  
Well Pattern ◽  
Late Neogene ◽  
Nanpu Sag ◽  
Sandstone Reservoirs

Natural fractures play an important role in the seepage system of Paleogene sandstone reservoirs at Nanpu Sag. Characteristics and formation mechanisms of natural fractures and stress-sensitivity permeability are comprehensively investigated and their impact on water injection is discussed based on core and log data (FMI and diplog data) as well as stress-sensitivity permeability measurement. Results show that high-angle shear fractures, including NE-SW strike fractures and NW-SE strike fractures, are widely developed in the study area, which were primarily developed during the late Paleogene and late Neogene. The present maximum horizontal principal stress is orientated at N60°–80°E, approximately parallel to the NE-SW fractures, contributing greatly to the seepage system at the early oilfield development stage. Fractures in the study area can be divided into three phases and are characterized by obvious stress-sensitivity permeability, which is closely related to fracture aperture and throat size. Since the fracture occurrence enhances stress sensitivity of permeability, it is necessary to regulate well pattern based on dynamic behaviors of fractured reservoirs at different development stages.

Quantitative Multiparameter Prediction of Fractured Tight Sandstone Reservoirs: A Case Study of the Yanchang Formation of the Ordos Basin, Central China

SPE Journal ◽  
2021 ◽  
pp. 1-32
Author(s):  
Jingshou Liu ◽  
Wenlong Ding ◽  
Haimeng Yang ◽  
Yang Liu
Keyword(s):  
Fractured Reservoirs ◽  
In Situ Stress ◽  
Stress Sensitivity ◽  
Central China ◽  
Fracture Aperture ◽  
Sensitivity Index ◽  
Tight Sandstone ◽  
Porosity And Permeability ◽  
Sandstone Reservoirs

Summary Fractured reservoirs account for more than one-half of the global oil and gas output and thus play a pivotal role in the world’s energy structure. Under diagenesis, rocks become dense, and tectonic fractures easily form under subsequent tectonic movement. These tectonic fractures are the main seepage conduits of tight sandstone reservoirs and are important determinants of whether a tight sandstone reservoir can have high, stable oil and gas production. The influence of multistage tectonic movement has led to well-developed fractures in the Ordos Basin in central China. In the process of reservoir development, the effective stress on the fracture surface increases because of the decrease in pore pressure, and the fracture aperture, porosity, and permeability also change accordingly. Therefore, modeling of the dual porosity and dual permeability of fractured reservoirs requires a dynamic 4D modeling process related to time. In this paper, we propose a 4D modeling method of dual porosity and dual permeability in fractured tight sandstone reservoirs. First, the porosity and permeability distribution of the reservoir matrix are established based on reservoir modeling. Based on geomechanical modeling, the density and occurrence of natural fractures are predicted by the paleostress field. The in-situ stress field is used to analyze the fracture aperture, and the variation in the fracture aperture during the development process is analyzed along with the variation in the in-situ stress in the development process to realize 4D modeling of the porosity and permeability of fractured reservoirs. The total porosity of the fracture is 0 to 8 × 10−3%, and the principal value of the planar permeability of the fracture is 0 to 3 × 10−3 µm2; the principal value of the fracture permeability is concentrated in the direction of 65 to 70° east-northeast. The simulated fracture porosity stress sensitivity index is distributed between 0 and 0.2, and the fracture permeability stress sensitivity index is distributed between 0 and 0.4. The Young’s modulus of the rock, in-situ stress parameters, and sound velocity in the rock are important factors affecting the fracture stress sensitivity.

Origin and formation mechanisms of low oil saturation reservoirs in Nanpu Sag, Bohai Bay Basin, China

2019 ◽  
Vol 110 ◽  
pp. 317-334 ◽  
Author(s):  
Jin Lai ◽  
Xiaojiao Pang ◽  
Feng Xu ◽  
Guiwen Wang ◽  
Xuechun Fan ◽  
...  
Keyword(s):  
Formation Mechanisms ◽  
Bohai Bay ◽  
Bohai Bay Basin ◽  
Oil Saturation ◽  
Nanpu Sag

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.

Integrated Solutions for the Redevelopment Plan of Offshore Mature-Oilfield

2021 ◽  
Author(s):  
Hongfu Shi ◽  
Yingxian Liu ◽  
Lifu Jiang ◽  
Jingding Zheng ◽  
Liqin Gan
Keyword(s):  
High Water ◽  
Bohai Bay ◽  
Sand Body ◽  
Well Pattern ◽  
Open Hole ◽  
Average Water ◽  
High Water Cut ◽  
Water Cut ◽  
Stream Lines ◽  
Sand Bodies

Abstract Abundant faults, long oil-bearing intervals (up to 500m), and diverse fluids including conventional oil and heavy oil, result in P oilfield became one of the most complex oil fields in the Bohai Bay. The main characters ofinitial development plan are directional well with commingle production, open hole completion, large draw down, high oil production rate, and reverse nine-point well pattern. At present, the oilfield has entered a stage of high water cut, with average water cut more than 85%. What can we do next, decommissioning or rebirthing? An integrated solution was proposed to redevelop the oilfield which focus on the layers’ subdivision, the fine description of the sand body,a large number of horizontal wells on the top of the water-flooded layer are used to tap the potential, increase the water injector to transform the stream lines and rebuild the reservoir pressure, and search for potential sand bodies to increase reserves.

A Comprehensive Model Integrating the Stress Sensitivity for Pressure Transient Behavior Study on the Two-Zone System for Offshore Loose Sandstone Reservoirs

2021 ◽  
Author(s):  
Chong Cao ◽  
Linsong Cheng ◽  
Xiangyang Zhang ◽  
Pin Jia ◽  
Wenpei Lu
Keyword(s):  
Flow Regimes ◽  
Transient Behavior ◽  
Stress Sensitivity ◽  
Composite Model ◽  
Zone Model ◽  
Well Testing ◽  
Comprehensive Model ◽  
Pressure Transient ◽  
Sandstone Reservoirs ◽  
Sandstone Formation

Abstract Permeability changes in the weakly consolidated sandstone formation, caused by sand migration, has a serious impact on the interpretation of well testing and production prediction. In this article, a two-zone comprehensive model is presented to describe the changes in permeability by integrating the produced sand, stress sensitivity characteristics. In this model, inner zone is modeled as a higher permeability radial reservoir because of the sand migration, while the outer zone is considered as a lower permeability reservoir. Besides, non-Newtonian fluid flow characteristics are considered as threshold pressure gradient in this paper. As a result, this bi-zone comprehensive model is built. The analytical solution to this composite model can be obtained using Laplace transformation, orthogonal transformation, and then the bottomhole pressure in real space can be solved by Stehfest and perturbation inversion techniques. Based on the oilfield cases validated in the oilfield data from the produced sand horizontal well, the flow regimes analysis shows seven flow regimes can be divided in this bi-zone model considering stress sensitive. In addition, the proposed new model is validated by the compassion results of traditional method without the complex factors. Besides, the effect related parameters of stress sensitivity coefficient, skin factor, permeability ratio and sanding radius on the typical curves of well-testing are analyzed. This work introduces two-zone composite model to reflect the variations of permeability caused by the produced sand in the unconsolidated sandstone formation, which can produce great influence on pressure transient behavior. Besides, this paper can also provide a more accurate reference for reservoir engineers in well test interpretation of loose sandstone reservoirs.

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