Natural Gas Geoscience ›› 2021, Vol. 32 ›› Issue (12): 1859-1866.doi: 10.11764/j.issn.1672-1926.2021.10.006

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Considerations on the strategy of volume fracturing for shale oil horizontal wells in Ordos Basin

Kuangsheng ZHANG(),Meirong TANG,Xianfei DU,Liang TAO()   

  1. Oil and Gas Technology Research Institute of Changqing Oilfield Company,PetroChina,Xi’an 710018,China
  • Received:2021-06-16 Revised:2021-10-09 Online:2021-12-10 Published:2021-12-27
  • Contact: Liang TAO E-mail:zks_cq@ petrochina.com;taoliangyouxiang@163.com
  • Supported by:
    The China National Science & Technology Major Project(2017ZX05069)

Abstract:

Shale oil in Ordos Basin has the characteristics of low pressure coefficient, low brittleness index and vertical multi-interlayer. Horizontal well and volume fracturing technology can greatly increase the production of single well, but it is difficult to achieve economic and effective development under low oil price. On the basis of big data's field practice in the basin, a quantitative evaluation method of volume fracturing effect was established, which puts forward the volume fracturing transformation strategy and the direction of the next project. On the basis of the establishment of a new sectional classification evaluation standard for the comprehensive geological engineering quality of horizontal wells and the fine classification of reservoir types, and based on the test results of fluid production profiles of 112 sections of nine horizontal wells, it was concluded that the fracturing segments of I and II reservoirs account for 85.2%, and the output accounts for 96.4%, which was the main productivity contribution section. The fracturing segments of III reservoirs account for 14.8%, and the output accounts for only 3.6%, with the lowest contribution. Therefore, priority is given to fracturing type I and II reservoirs, and selective fracturing of III reservoirs. The main factors affecting productivity are reservoir length, fluid injection strength, fracture density, brittleness index, sand addition strength, permeability, discharge, porosity, horizontal stress difference and oil saturation. The material basis of reservoir is the first condition to obtain high productivity, and increasing the sweep volume of fracture net is an important way to maximize the productivity of unconventional oil and gas. The research results can provide a scientific basis for the optimal design of volume fracturing of shale oil horizontal wells and effectively promote the scale benefit development of shale oil.

Key words: Ordos Basin, Shale oil, Volume fracturing, Fluid production profile, Reconstruction strategy

CLC Number: 

  • TE234+.1

Table 1

Characteristic parameter comparison of the shale oil in Ordos Basin and that in other areas home and abroad"

特征参数鄂尔多斯盆地 延长组国内盆地国外盆地
准噶尔盆地芦草沟组三塘湖盆地条湖组松辽盆地白垩系北美二叠盆地
沉积环境湖相湖相湖相湖相浅海相
埋深/m1 600~2 2002 700~3 9002 000~2 8001 700~2 2002 134~2 895
油层厚度/m5~1510~135~2010~30400~600
孔隙度/%6~128~14.68~185~188~12
渗透率/(10-3 μm20.11~0.140.01~0.0120.1~0.50.02~0.50.01~1.0
含油饱和度/%67.7~72.478~8055~76.548~5575~88
气油比/(m3/t)75~12218~22//50~140
原油黏度/(mPa·s)1.21~1.9611.7~21.558~834.0~8.00.15~0.53
压力系数0.77~0.841.2~1.60.91.1~1.321.05~1.5
水平应力差/MPa4~65~91~53~61~3
脆性指数/%35~4550~5131~54/45~60

Fig.1

Plane display map of microseismic events of volume fracturing in horizontal wells"

Fig.2

Correction of fracture net sweep volume productivity of shale horizontal wells"

Fig. 3

Comparison of effective fracture net sweep volume and coefficient of typical platform"

Table 2

Evaluation criteria for RQ and CQ classification of shale oil horizontal wells in Ordos Basin"

综合

品质

储层品质(RCQ)
I类II类III类

工程

品质

A

Φe≥5%,So≥70%

σh≤30 MPa,BI≥50%

3≤Φe<5%,50≤So<70%

σh≤30 MPa,BI≥50%

Φe<3%,So<50%

σh≤30 MPa,BI≥50%

B

Φe≥5%,So≥70%

30<σh≤34 MPa,40≤BI<50%

3≤Φe<5%,50≤So<70%

30<σh≤34 MPa,40≤BI <50%

Φe<3%,So<50%

30<σh≤34 MPa,40≤BI <50%

C

Φe≥5%,So≥70%

σh>34 MPa,BI <40%

3≤Φe<5%,50≤So<70%

σh>34 MPa,BI <40%

Φe<3%,So<50%

σh>34 MPa,BI <40%

Fig.4

Test pattern of fluid production profile of each fracturing section of shale oil horizontal well"

Fig.5

Comparison diagram of the number, input and output ratio of different types of shale oil reservoirs"

Fig.6

Correlation diagram of some geological engineering parameters and production of shale oil horizontal well"

Fig.7

Ranking chart of factors affecting production"

Fig.8

Correlation diagram between different types of shale oil reservoirs and cumulative oil production"

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