水平井随钻C/O能谱测井影响因素的蒙特卡罗模拟研究

Monte Carlo simulation for C/O spectroscopy logging while drilling in the horizontal well

C/O能谱测井是确定含油饱和度的主要测井方法,在随钻条件下可以通过记录非弹性散射伽马能谱,根据C/O值来确定原始地层的含油饱和度。利用蒙特卡罗方法模拟水平井条件下不同岩性、孔隙度、饱和度、井眼尺寸、钻井液性质以及钻井液侵入、地层水矿化度、泥质含量、油气类型和源距时的非弹性散射伽马能谱,研究C/O值与含水饱和度、孔隙度的关系以及各种因素对测井响应的影响。在水平井条件下C/O值与含水饱和度呈线性相关,油基钻井液和石灰岩地层的C/O值大;井眼尺寸越小、地层水的矿化度越高、骨架中泥质越多以及源距越大时,地层的C/O值越大;钻井液侵入随着侵入深度、岩性、孔隙度和钻井液类型的不同对C/O的影响规律不同。钻井液侵入越浅、井眼尺寸越小、孔隙度越大、油质越重,利用C/O能谱测井识别地层流体越有利。

C/O logging is a main logging method that can determine oil saturation.The oil saturation of initial formation can be determined by C/O according to the inelastic gamma spectroscopy in LWD（logging while drilling）.The inelastic gamma spectrum were simulated using the Monte Carlo method under the condition of different lithology,porosity,saturation,borehole size,mud and mud invasion,water salinity,shale content,hydrocarbon and source-receiver spacing in horizontal wells.The response of C/O and porosity and saturation was studied,and the effects of several factors on C/O values were given.It is concluded that the relationship of C/O value and oil saturation is linear.C/O values are high when with oil-based mud in boreholes or in limestone formation.The smaller the hole size,the higher the formation water salinity,the more the shale content in the matrix and the bigger the spacing,the greater the formation C/O value.C/O values are affected differently as mud invasion depth,lithology,porosity and drilling mud change.It is favorable to identify formation fluid by using C/O spectroscopy logging under the condition of small mud invasion depth,small borehole size,high porosity and heavy oil.