| Author's Name: CHENG Tao, MA Yongxin, ZHOU Wei, LIU Pengchao, HUI Zengbo,
GE Jiayu, CHEN Jia, FENG Congjun |
| The Pliocene Yinggehai Member 2 of Dongfang Gasfield in Yinggehai Basin is characterized by littoral and
shallow marine facies, which is mainly composed of thick mudstone intercalated with low permeability siltstone. In order
to realize the sustainable development and utilization of natural gas in Dongfang Gasfield, it is urgent to clarify the “sweet
spot” distribution of low permeability reservoir. Taking the Ⅰgas formation of Yinggehai Member 2 (N2 y2-Ⅰ) of Dongfang
Gasfield as an example, based on the comprehensive application of 3D seismic data, logging data, production data, and
other data, the research on prediction and classification of “sweet spot” in low permeability reservoirs is carried out by the
use of logging constrained sparse pulse inversion method, and the analysis of the main controlling factors (sedimentary
microfacies) of “sweet spot”.
The results show that the P-wave impedance of the low-permeability gas-bearing reservoir (“sweet spot”) in N2 y2-Ⅰis
less than 5.6×106 (kg/m3•m/s). The classification and identification criteria for “sweet spot” of low permeability reservoirs
has been established through the crossplot analysis of P-impedance between porosity, permeability, water saturation, and
thickness in N2y2-Ⅰ. There are three types of “sweet spot”. The type Ⅰ is located in the main body of shoreface bar,
with the P-impedance less than 5.0×106 (kg/m3•m/s), the permeability more than 20×10-3 μm2, the production more
than 10×104 m3/(d·m), the thickness of gas formation more than 10 m, and the water saturation less than 55%. The type
Ⅱ is also located in the main body of shoreface bar, with the P-impedance among (5.0-5.3) ×106 (kg/m3 •m/s), the
permeability among (10-20)×10-3 μm2, the production among (5-10) ×104 m3/(d·m), the thickness of gas layer among 5-
10 m, and the water saturation among 55%~65%. The type Ⅲ is located at the edge of shoreface bar, with the P-impedance
among (5.3-5.6) ×106 (kg/m3•m/s), the permeability less than 10×10-3 μm2, the production less than 5×104 m3/(d · m), the
thickness of gas formation less than 5 m, and the water saturation more than 65%. Generally, the “sweet spot” of type Ⅰ
and type Ⅱare mainly distributed in strips in the main body of shoreface bar; the type Ⅲ is distributed in flaky shape on
the edge of shoreface bar. This method is mainly applicable to the reservoirs with obvious P-impedance difference, and its
reasonable application can effectively determine the plane distribution of “sweet spot”, so as to provide guidance for the
sustainable development of oil and gas fields. |
