Academic Journal of Science and Technology 
ISSN: 2771-3032 | Vol. 14, No. 2, 2025 

 

288 

Development	Unit	Division	of	Low	Permeability	
Reservoir	in	Y	Block,	Ordos	Basin	
Ruijun He, Jiaxi Huang and Tao Shen 

School of Xi’an, Shiyou University, Shaanxi 710000, China 

 

Abstract: The Y block reservoir in Ordos Basin is a typical low porosity and permeability tight sandstone reservoir with poor 
physical property and strong heterogeneity. On the plane, the small layer sand body Changes quickly, the continuity is poor, the 
pressure distribution is uneven, and the principal side effect is uneven. In the section, the liquid production in the stratification 
is not clear, the washing degree of the small layer is different, and the water contradiction in the multi-direction of the single 
layer is prominent. At present, the overall reservoir decline is fast, some Wells have low productivity and high water cut, and 
most of the Wells have more open layers. In this paper, based on geological factors and development dynamic factors, combined 
with fracture identification, the first development unit of Y block reservoir is divided, and on the basis of the first development 
unit division, the second development unit is further divided according to the situation of small layer division and correlation. 
The division of the secondary development units can correspond the development contradiction to the small layer, and has 
guiding significance for the evaluation of the subsequent reservoir development effect and the fine adjustment of development 
policy. 

Keywords: Low permeability reservoir; Partition parameter correlation analysis; Development unit division. 
 

1. Introduction 
Oil and gas resources are a relatively important energy in 

our country. China has been committed to developing 
traditional conventional oil and gas energy. However, with the 
application of energy, traditional conventional oil and gas 
energy gradually becomes unable to support daily 
consumption, so energy development gradually shifts from 
conventional oil and gas energy to unconventional oil and gas 
energy. Unconventional oil and gas resources mainly refer to 
shale oil, shale gas, coalbed methane and tight gas. It is of 
great significance to accelerate the development of 
unconventional oil and gas energy. Block Y, located in the 
middle part of Yishan Slope in Ordos Basin, is a typical large 
complex stratigraphic and lithologic trap gas reservoir with 
low permeability, low abundance and low production. The 
main development horizon is the Middle Jurassic Yan 'an 
Formation and the Upper Triassic YanChang Formation. The 
reservoir type is mainly dolomite solution cavity, and the 
reservoir plane has strong heterogeneity. Due to the "three-
low" characteristics and strong heterogeneity of gas reservoirs, 
it brings great challenges to the balanced exploitation of gas 
fields. The division of development units is an important 
means to improve the management level of gas fields. 
Through the reasonable division of development units, gas 
Wells with similar regional production dynamic 
characteristics are regulated, and targeted development 
technology policies are formulated to achieve fine dynamic 
evaluation and adjustment of gas reservoirs, so as to improve 
the development effect of gas sacks.  

2. Geological Setting 
Ordos Basin, located in the central and western part of 

North China Plate, is the second largest sedimentary basin in 
China. It is a giant craton superimposed basin with a total area 
of 37×104km2 formed by continuous cyclic evolution and 
various sediments. The whole shape of the basin is rectangular, 

in which the east and west span is large, surrounded by 
mountains, and there are 6 structural units. From the overall 
structural characteristics, it is a monoclinal structure with 
high east and low west slope. The surface is covered with 
Quaternary loess, the surface gullies are interlinked, the 
landform belongs to the typical northwest Danxia landform, 
the climate is dry. At present, the accumulation area of oil and 
gas resources in the basin has the characteristics of large area 
and wide distribution, and the formed reservoirs are 
characterized by simple structure, stable sedimentation, 
complex pore throat structure and natural micro-fracture 
development, etc. Most of them belong to low porosity and 
ultra-low permeability sandstone reservoirs. The study area is 
Tiebiancheng Block of Ordos Basin, whose structural 
location belongs to the transitional zone between Yishan 
Slope and Tianhuan depression of Ordos Basin. The overall 
structural morphology is relatively gentle, the overall regional 
stratum relief Angle is < 1.0°, and a series of low-amplitude 
nose uplift structures are developed in the east-west direction, 
with a uplift amplitude of 10~20m and a nose uplift axis width 
of 2~5km. The structure has good inheritance; The main oil-
bearing development strata are the Middle Jurassic Yan 'an 
Formation and the Upper Triassic YanChang Formation.  

3. Development Unit Division Basis 

3.1. Geological basis 
The geological basis for the division of development units, 

starting with the division and comparison of small layers, 
studies the planar distribution of sedimentary microfacies and 
the thickness distribution of sand bodies in block Y, defines 
the characteristics of sedimentary microfacies, and analyzes 
the distribution and connectivity of single sand bodies on the 
basis of the study of sand body distribution. Finally, combined 
with the identification of cracks, the geological basis is 
analyzed comprehensively. 

3.1.1. Small layer division and contrast 
In this paper, based on the application of logging and 



 

289 

drilling data in Block Y, the Chang 4+5 oil formation in Block 
Y is divided into two sand groups: Chang 4+51 and Chang 
4+52, and the Chang 4+51 subgroup is subdivided into Chang 
4+51

1 and Chang 4+51
2 subgroups, and the Chang 4+52 

subgroup is subdivided into Chang 4+52
1 and Chang 4+52

2 
subgroups. Further Chang 4+51

1 layers can continue to be 
divided into 3 sub-layers, Chang 4+51

2 layers can continue to 

be divided into 2 sub-layers, Chang 4+52
1 layers can continue 

to be divided into 3 sub-layers, Chang 4+52
2 layers can 

continue to be divided into 2 sub-layers. The Chang 61 sand 
formation is subdivided into Chang 61

1 and Chang 61
2 layers, 

and the further Chang 61
1 layers can be further divided into 

two secondary layers. The Chang 61
2 layers can be further 

divided into three sub-layers (Figure 3-1). 
 

 
Figure 3-1. Y small layer correlation scheme 

 
3.1.2. Small layer division and contrast 

The distribution of sedimentary microfacies in Y block was 
characterized through core observation and literature 
investigation in the study area. The sedimentary microfacies 
of each small layer in Block Y are mainly composed of 

underwater distributary channels and underwater 
interdistributary bays. According to the sedimentary 
microfacies Changes of each small layer, it can be seen that 
the sedimentary process from Chang 61

2-3 to Chang 4+51
1-1 is 

a three-stage sedimentary process with large water recession-
water inflow and then fluctuation (FIG. 3-2~ FIG. 3-5). 

 

Figure 3-2. Sedimentary microfacies map of 
Chang 4+51

1-1 reservoir in block Y 
Figure 3-3. Sedimentary microfacies map of 

Chang 4+52
1-3 reservoir in Block Y 

 

Figure 3-4. Sedimentary microfacies map of 
Chang 61

2-2 reservoir in Block Y 
Figure 3-5. Sedimentary microfacies map of 

Chang 61
2-3 reservoir in Block Y 

AC
150 350us/m

ILD
0 50ohm·m

GR
0 201API

SP
50 100MV

解
释
结
论

分
层

D
E
P
T
H

长4+51
1

长4+51
2

长4+52
1

长4+52
2

长61
1

长61
2



 

290 

 

3.1.3. Small layer division and contrast 
Through the core observation of Block Y in Tiebiancheng 

area, this study confirms that the reservoir in this area is 
mainly gray sandstone. On the basis of core observation and 
small layer division and analysis of logging data, the 
thickness distribution of sand body in Y block is obtained. The 
sand bodies are distributed in a NE-SW direction, controlled 
by the microfacies of distributary channel. The sand bodies of 
main reservoirs in Y block Chang 61

2-2, Chang 61
1-2, Chang 

4+52
2-2 and Chang 4+52

1-3 have large overall thickness and 
good continuity, and the sand bodies at the intersection of 
channels have large thickness. 

3.1.4. Small layer division and contrast 
On the basis of the study of sedimentary microfacies 

distribution and sand body thickness distribution in the study 

area, the plane distribution of single sand body in the study 
area is obtained according to the distribution map of sand 
body thickness, sedimentary microfacies and single sand 
body in block Y: The underwater distributary channels control 
the single channel, with a total of 8-15 single sand-body 
channels, and the lateral contact relationship of each single 
channel is mainly superimposed and cut overlapping. The 
sand thickness is large at the intersection of the single channel 
(Figure 3-6, Figure 3-7). In the direction of parallel source, 
the single sand body has good connectivity, and the 
superposition relationship is mainly characterized as 
superposition and cut superposition. In the vertical source 
direction, the overall connectivity of the sand body is 
relatively weak, and the superposition relationships are 
mainly isolated, superimposed, and occasionally tangential. 

 

  
Figure 3-6. Plane layout of single sand body of 

reservoir Chang 4+52
1-3 in block Y 

Figure 3-7. Plane layout of single sand body of 
reservoir Chang 61

2-2 in block Y 
 

3.1.5. Small layer division and contrast 
The porosity distribution of Chang 4+5 layer samples in 

block Y ranges from 0.51% to 27.69%, with an average 
porosity of 13.11%. The porosity distribution of Chang 6 
layer samples ranges from 0.51% to 27.69%, and the average 

porosity is 13.07%. The permeability distribution of Chang 
4+5 layer samples ranges from 0.01 to 58.91mD, and the 
average permeability is 0.63mD. The permeability 
distribution of the long 6 layer samples ranged from 0.01 to 
11.54mD, and the average permeability was 0.65mD (Figure 
3-8 to Figure 3-9). 

 

 

Figure 3-8. Histogram of porosity distribution 
in block Y 

Figure 3-9. Histogram of permeability distribution in 
block Y 

 

3.1.6. Small layer division and contrast 
The characteristics of fracture development in the study 

area are studied by the method of dynamic and static 
combination. The qualitative and quantitative evaluation of 
fractures is carried out by means of static core observation and 

tracer test, and the influence of fracture development on 
actual production is analyzed dynamically by combining 
production dynamic data and water flooding law. In Block Y, 
42 Wells were identified as having developed fractures 
(Figure 3-10). 

 



 

291 

 
Figure 3-10. Crack identification map of block Y 

 

3.2. Development basis 
3.2.1. Development status 

The oil reservoir in Block Y was established in 2005, with 
an oil bearing area of 99.49km2, geological reserves of 
34.654,000 tons, and annual oil capacity of 81,000 tons. 
Currently, the main reservoirs are long 4+522 and long 612, 
and the well pattern adopts 480×160m diamond-shaped 
reverse nine spot well pattern. The average reservoir 
thickness of the reservoir parameters is 10.9m, and the 
porosity is 12.2%. Permeability 0.83mD. In area Y, water 
injection has been developed since November 2006. 
According to the production dynamic data, by the end of 
December 2023, 258 oil Wells and 100 water Wells have been 
drilled, with a daily production level of 164.4t and a single 
well production capacity of 0.64t/d. Daily injection level 
2084.8m3 The daily injection water of a single well is 20.8m3, 
and the current comprehensive water cut is 59%. At present, 
the reservoir is developed with a set of multi-layer well 
pattern, and the reservoir is highly heterogeneous. In the plane, 
the small layer sand body Changes rapidly, the continuity is 

poor, the pressure distribution is uneven, and the main lateral 
efficiency is uneven. The stratified liquid production is not 
clear, the washing degree of small layers is different, and the 
water contradiction of single layer is prominent in multiple 
directions. In the process of division of development units, the 
development basis mainly refers to the current water content, 
pressure distribution and water-seeing effect type. 

3.2.2. Current moisture content and type of water-seeing 
effect 

According to the current water cut data of Y reservoir, the 
water cut map for 2023 is drawn (FIG. 3-11). By using the 
water intake profile and combining with the dynamic 
production data, the water-seeing effect types of the 
producing oil Wells in the whole area of Y block are identified. 
The proportion was 72.48%, and the effective water-seeing 
type accounted for 23.39%. The effective water-finding type 
occupies a certain proportion, reflecting the existence of 
reservoir fractures or waterflood hyperpermeability zones in 
the study area. (Figure 3-12) 

 

  
Figure 3-11. Y reservoir water cut distribution 

map for 2023 
Figure 3-12. Y reservoir oil well water response 

type diagram 
 

3.2.3. Current pressure distribution and individual well 
productivity 

Based on the current pressure measurement data of block 

Y, the pressure distribution map in 2023 is drawn (FIG. 3-13), 
and the production dynamic data is used to draw the 
production capacity map of the oil Wells in the whole region 
Y in 2023 (FIG. 3-14). 

 



 

292 

  
Figure 3-13. Y Reservoir pressure profile for 

2023 
Figure 3-14. Y reservoir single well productivity 

map 
 

4. Develop Unit Partitioning Methods 
The division method of development units is based on the 

basic geological research, the comprehensive evaluation of 
reservoir as the starting point, the identification of fractures 
and the actual development dynamics, and the division results 
of development units are obtained, which are convenient for 
later development effect evaluation and development policy 
adjustment. 

4.1. Partition parameter correlation analysis 
Based on the correlation analysis of sand thickness, sand-

ground ratio, porosity, permeability, effective reservoir 
thickness, and individual well productivity of the main oil-
producing layer 4+521 in block Y, the system cluster analysis 
pedigree and correlation heat map of each parameter are 
obtained. By analyzing the cluster analysis pedigree and 
correlation heat map, the correlation characteristics of each 
parameter can be obtained. In other words, the sand thickness 
is strongly positively correlated with the effective thickness 
of the oil reservoir, the sand-land ratio is strongly positively 
correlated with the effective thickness of the oil reservoir, and 
the porosity is weakly positively correlated with the effective 
thickness of the oil reservoir. (Figure 4-1, Figure 4-2) 

 

  
Figure 4-1. Chang 4+52

1 small reservoir parameters 
cluster analysis pedigree 

Figure 4-2. Parameter correlation heat map of Chang 
4+52

1 small reservoir 
 

4.2. Development unit division 
In this research, the division of development units is mainly 

based on sand thickness, sand to ground ratio and effective 
reservoir thickness, and is modified in combination with 
fracture development characteristics, production horizon, 
current water cut and response type, so as to divide the Y 
block reservoir into primary development units. On the basis 
of the division of primary development units, according to the 
division and comparison of small layers, four main 
production small layers are selected, and the four main 
production small layers are divided into secondary 
development units by mainly referring to sand thickness, sand 
to ground ratio and effective oil layer thickness, and 
combining with the distribution of single sand body, fracture 
development characteristics, current water content and 

effective type. 

5. Development Unit Division Results 

5.1. Result of division of first-level 
development units 

In order to provide a basis for the further development of 
the oilfield, this study divided the reservoir of block Y into 8 
first-level development units (Figure 5-1) based on the 
previous geological knowledge and relevant development 
dynamic research results, combined with the identification of 
fractures, and considering the maximum integrity of 
injection-production units and the convenience of the 
adjustment of the water injection scheme in the later stage. 

 



 

293 

 
Figure 5-1. Division and sand thickness of primary 

development unit in Y reservoir 
 

5.2. Results of secondary development unit 
division 

On the basis of the division of first-level development units, 
the reservoir in Block Y was divided into 16 second-level 
development units according to the four main production 
units according to the division and correlation of small layers, 

in order to map the development contradictions to the small 
layers in a targeted way, and analyze the injection and 
production correspondence of small layers, the distribution of 
fractures in small layers, and the main controlling factors of 
water breakthrough effect in a more intuitive way (Figure 5-
2~ Figure 5-5). 

 

  
Figure 5-2. Plot and porosity of Chang 4+52

1 
small layer development units 

Figure 5-3. Mapping and sedimentary microfacies 
of Chang 4+52

2 small layer development units 

  
Figure 5-4. Chang 61

1 small layer development 
unit division map and water content 

Figure 5-5. Chang 61
2 small layer development 

unit division map and permeability 
 

6. Summary 
In order to provide a basis for the further development of 

the oilfield, this project takes the previous geological 
understanding and relevant development dynamic research 
results as a reference, combined with the identification of 
fractures, considering the maximum integrity of injection-
production units and the convenience of later water injection 

plan adjustment, and divides the Y block reservoir into first-
level development units, and on the basis of first-level 
development unit division, The four main production zones 
are divided into 16 secondary development units. After the 
division of the primary development units, the effective 
thickness distribution, water cut distribution, fracture 
distribution and individual well productivity distribution in 
each area of the Y block reservoir can be generally grasped, 



 

294 

which helps to refine the development status and development 
contradictions into small layers when the secondary 
development units are divided. These 16 secondary 
development units are divided into 4 main production zones 
respectively. According to the division results of secondary 
development units, subsequent work such as natural decline 
rate, horizontal waterflood rule, injection-production 
correspondence, and waterflood development effect 
evaluation of each development unit can be targeted at the 
small-layer level to analyze the fine correspondence of 
injection-production, fracture distribution, and main control 
factors of water emergence effect. This study is of guiding 
significance for the subsequent refinement and adjustment of 
reservoir development policy of this subject, and can also 
provide reference for the preliminary preparation for the 
evaluation of the development effect of similar reservoirs. 

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