Application of Vertical P⁃Wave Slowness in Porosity Evaluation of Shale Gas Reservoirs in Highly Deviated or Horizontal Wells

摘要/Abstract

摘要： In Changning Shale Gas Pilot Development Area of Sichuan basin and based on vertical wells, a parameter model is built by using density, neutron, P-wave slowness, GR and resistivity logging data and core porosity and saturation to evaluate the resources. Horizontal well is used to develop the shale gas in the area. A parameter model is established with the same logging data from horizontal wells and core porosity and saturation from vertical wells to evaluate reservoirs in horizontal wells. P-wave slowness is the basic data for building the porosity and rock mechanical parameter model. The results show that the P-wave slowness measured in vertical wells is greater than those measured in highly deviated wells and horizontal wells in the Changning shale gas area. The P-wave slowness is greatly affected by well deviation, and the larger the well deviation, the greater the influence because of obvious velocity anisotropy in vertical and horizontal directions. In the same horizon and the same well interval, the porosity calculated from the model in highly deviated or horizontal wells is significantly different from the core porosity. In this study, we analyzed the relationships between P-wave slowness and well deviation in the same interval of the vertical, highly deviated and horizontal wells in the study area, and compared the P-wave slowness and porosities calculated by direct fitting method and anisotropic elliptic model method. It is considered that both of the two methods can reduce the influences of anisotropy and the anisotropic elliptic model method works better. Finally, the anisotropic elliptic model method has been widely used in porosity evaluation of shale reservoirs and good results have been gained in the study area.

关键词: Sichuan Basin, Changning Shale Gas Pilot Development Area, shale gas, highly deviated well, horizontal well, anisotropy, vertical P-wave slowness, porosity

Abstract: In Changning Shale Gas Pilot Development Area of Sichuan basin and based on vertical wells, a parameter model is built by using density, neutron, P-wave slowness, GR and resistivity logging data and core porosity and saturation to evaluate the resources. Horizontal well is used to develop the shale gas in the area. A parameter model is established with the same logging data from horizontal wells and core porosity and saturation from vertical wells to evaluate reservoirs in horizontal wells. P-wave slowness is the basic data for building the porosity and rock mechanical parameter model. The results show that the P-wave slowness measured in vertical wells is greater than those measured in highly deviated wells and horizontal wells in the Changning shale gas area. The P-wave slowness is greatly affected by well deviation, and the larger the well deviation, the greater the influence because of obvious velocity anisotropy in vertical and horizontal directions. In the same horizon and the same well interval, the porosity calculated from the model in highly deviated or horizontal wells is significantly different from the core porosity. In this study, we analyzed the relationships between P-wave slowness and well deviation in the same interval of the vertical, highly deviated and horizontal wells in the study area, and compared the P-wave slowness and porosities calculated by direct fitting method and anisotropic elliptic model method. It is considered that both of the two methods can reduce the influences of anisotropy and the anisotropic elliptic model method works better. Finally, the anisotropic elliptic model method has been widely used in porosity evaluation of shale reservoirs and good results have been gained in the study area.

Key words: Sichuan Basin, Changning Shale Gas Pilot Development Area, shale gas, highly deviated well, horizontal well, anisotropy, vertical P-wave slowness, porosity

ZHENG Jian, FU Yongqiang, CHEN Man, JING Cui, ZHANG Jing, ZHOU Hao, ZHANG Jiahao. Application of Vertical P⁃Wave Slowness in Porosity Evaluation of Shale Gas Reservoirs in Highly Deviated or Horizontal Wells[J]. 新疆石油地质, 2021, 42(zk(English)): 158-164.

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