水平井密度测井影响因素的蒙特卡罗模拟研究

Monte Carlo Simulation on Influence Factors of Density Logging in Horizontal Well

水平井随钻过程中的密度测井要受井眼尺寸、仪器和井壁的间隙、泥浆比重(含氢量)、泥饼、岩屑、水垫、泥浆侵入等环境影响。利用蒙特卡罗方法模拟水平井在改变井眼半径、地层岩性、孔隙度、岩屑厚度、储层厚度、水垫和泥浆侵入深度等条件的伽马能谱,则井眼尺寸和水垫厚度越大,远近探测器的伽马计数越高,且直线的斜率大小反映对远近探测器的影响大小;岩屑厚度越大,近探测器比远探测器的伽马计数率变化越快,地层的密度动态变化范围越小;泥浆侵入使远近探测器的伽马计数减小,且近探测器变化快,侵入深度达到12 cm后伽马计数率几乎不发生变化。水平井密度测井的探测深度大约为15 cm,为地质导向提供了理论指导作用。

The horizontal well technique has been used widely in oil development. The LWD density logging was influenced by several factors such as bore size, stand off between logging tool and borehole wall, mud density, mud cake, cuttings, water cushion and mud invasion. The gamma spectra were simulated by Monte Carlo method under different conditions of bore size, forma- tion lithology, porosity, reservoir thickness, thickness of cuttings layer and water cushion, and invasion depth in horizontal well. The count rate of far or near gamma ray detector increases as the bore size or water cushion thickness increases, and their slopes reflect different influences on the two detectors. When the thickness of cuttings layer increases, the near count rate increases faster than the far one; and the dynamic range of formation density decreases. Mud invasion causes decrement of both count rates, and the near one varies faster than the far one, but the gamma count rate will be changeless when the depth of invasion reaches 12 cm. The investigation depth of density logging in horizontal well is about 15 cm.