Research and application of the prediction method for sweet spots of shale gas using geophysical data By Sheng Chen,
The W1 area in the Sichuan Basin is the first
Wenzhi Zhao,
area for shale gas exploration and development
the US, but shale gas production is more
Yonglin Ouyang,
in China.This is a case study carried out in the
challenging in China. Shale gas exploration and
Qingcai Zeng, Qing
area’s Lower Silurian Longmaxi Formation,
development has only recently begun in China
Yang Huaxing Hou,
which has great resource potential. Many
and seismic-based prediction of sweet spots is
Shaohua Gai, Shihai
scholars have carried out a great deal of
still in its infancy.
Bao and Xinyu Li.
research work, such as the division of sedi
Shale gas potential is similar in China and
Prediction of sweet spots is one of the most
mentary facies, selection evaluation, reservoir
important procedures in shale gas exploration
core experiments and so on, and the core area
and development. A sweet spot of shale gas is
has been preliminarily determined in the W1
defined as an area with moderate burial depth,
area. But geophysical prospecting of sweet
high organic carbon content, high maturity,
spots is just at its beginning and thus has not
high gas content, high brittle mineral content,
provided enough information for the deploy
well-developed natural fractures and the easy
ment of horizontal well drilling.
formation of complex fracture network by
In our study, firstly we used well log interpre
fracturing. It is the preferred target for acquir
tation to determine key evaluation parameters
ing and maintaining high productivity and
of the shale reservoir at the well point, and to
realising the effective production of shale gas.
study the vertical distribution and variation of
Gas content, which is one of the key elements
the shale reservoir; in this way we could deter
of sweet spots, has great significance to the
mine the longitudinal distribution of sweet spots.
commercial development of shale gas reservoirs.
Secondly, seismic rock physics analysis was used
Kevin J. Dodds et al. (2007), based on core
to find the elastic parameters that were sensi
analysis results and well log data, applied a
tive to the key evaluation parameters, such as
neural network method to establish a relation
total organic carbon (TOC) and the gas content
ship between seismic attributes and gas satur
of the shale gas reservoir. At the same time the
ation through a seismic attribute analysis and
quantitative relationships between them were
obtained some positive effects in computing
established. Finally, based on the results of
the gas saturation of a shale reservoir with
seismic rock physical analysis, high quality
seismic attributes.
pre-stack inversion was carried out with the
Daniel J.K. Ross et al. (2009), based on a
combination of well and 3D seismic data, which
detailed analysis of pore structure, TOC and
was used to predict the plane distribution of
pore fluid composition in the shale reservoir,
the thickness, TOC content, brittleness, pore
suggested that the gas content was closely
pressure and other key evaluation parameters
related to porosity and TOC, and basically
of shale reservoir. Comprehensive analysis of
established the quantitative relationship
the research results was used to determine the
between gas content and porosity or TOC
distribution of sweet spots.
on the basis of well data.
46 R e s e a r c h a n d a p p l i c a t i o n o f t h e p r e d i c t i o n m e t h o d f o r s w e e t s p o t s o f s h a l e g a s u s i n g g e o p h y s i c a l d a t a
