基于测井约束稀疏脉冲反演的低渗储层“甜点”预测及分类评价——以莺歌海盆地东方气田莺二段Ⅰ气组为例

Prediction and classification of “sweet spot” in low permeability reservoir based on logging constrained sparse pulse inversion:a case study ofⅠgas formation of Yinggehai Member 2 in Dongfang Gasfield, Yinggehai Basin

莺歌海盆地东方气田上新统莺歌海组二段发育滨浅海相沉积,岩性总体以厚层泥岩夹低渗粉砂岩为主。为实现东方气田天然气持续开发利用,亟需明确低渗储层“甜点”展布特征。以东方气田莺二段Ⅰ气组为例,综合应用三维地震、测井、生产动态等资料,采用测井约束稀疏脉冲反演方法,在明确沉积微相控制低渗储层“甜点”展布的基础上,开展“甜点”预测;优选纵波阻抗、含水饱和度、渗透率、产能等参数开展分类评价研究。研究结果表明莺二段Ⅰ气组低渗含气储层(“甜点”)的纵波阻抗小于5.6×10^(6)(kg/m^(3)·m/s),“甜点”可划分为3类:Ⅰ类、Ⅱ类“甜点”呈条带状分布,主要分布于临滨砂坝主体;Ⅲ类“甜点”呈片状分布,分布于临滨砂坝边缘。本方法主要适用于储层纵波阻抗特征差异明显的区域,可以通过该方法的合理应用有效厘定各类“甜点”的平面展布,从而为油气田持续开发提供指导。

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 theⅠgas formation of Yinggehai Member 2(N_(2)y^(2)-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 N_(2)y^(2)-Ⅰis less than5.6×10^(6)(kg/m^(3)·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 N2y~2-Ⅰ.There are three types of“sweet spot”.The typeⅠis located in the main body of shoreface bar,with the P-impedance less than5.0×10^(6)(kg/m^(3)·m/s),the permeability more than 20×10^(-3)μm^(2),the production more than 10×10^(4)m^(3)/(d·m),the thickness of gas formation more than 10 m,and the water saturation less than 55%.The typeⅡis also located in the main body of shoreface bar,with the P-impedance among(5.0-5.3)×10^(6)(kg/m^(3)·m/s),the permeability among(10-20)×10^(-3)μm^(2),the production among(5-10)×10^(4)m^(3)/(d·m),the thickness of gas layer among 5-10 m,and the water saturation among 55%~65%.The typeⅢis located at the edge of shoreface bar,with the P-impedance among(5.3-5.6)×10^(6)(kg/m^(3)·m/s),the permeability less than 10×10^(-3)μm^(2),the production less than5×10^(4)m^(3)/(d·m),the thickness of gas formation less than 5m,and the water saturation more than 65%.Generally,the“sweet spot”of typeⅠand typeⅡare mainly distributed in strips in the main body of shoreface bar;the typeⅢis 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.