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本文描述了将随钻测井(LWD)中子孔隙度和密度的耐温指标提高到175℃所进行的努力。已研制出新的锂6(Li-6)闪烁体探测器,并在不同的温度条件下测试评价了其性能。试验测试结果表明这种新的探测器在175℃时的寿命可与目前150℃时的探测器相媲美。为了预测新探测器外壳和防护层在高温、高压条件可能出现的变形,已对其力学部分进行了研究。有限元分析(FEA)模拟结果表明:该仪器在高温高压(175℃、30,000psi)情况下仍可保持机械完整性。采用蒙特卡罗N粒子输运代码系统(MCNP)验证探测器封装对仪器响应和中子孔隙度测量的影响。模拟结果表明新型探测器外壳在标准的孔隙度测量范围内对中子孔隙度测量的影响极小。另外,根据在不同温度下的大量模拟结果,开发出了一种新的用于中子孔隙度测量的温度校正算法。特别是当测井温度极高时,该算法比当前在用的更为精确。本底扣除算法已被精细调整以适用于高温度时的高噪音等级。采用不同孔隙度和井眼大小的水饱和的石灰石、砂岩和白云岩地层,在实验室对整个升级仪器进行了校正和表征。实验结果表明:该仪器读数与公认的实验室地层孔隙度具有很好的一致性。
This article describes the effort to increase the temperature tolerance of LWD neutrons to 175 ° C. New Lithium 6 (Li-6) scintillator detectors have been developed and tested for their performance under different temperature conditions. Test results show that the new detector at 175 ℃ life expectancy with the current 150 ℃ when the detector is comparable. In order to predict the possible deformation of the new detector shell and the protective layer under high temperature and high pressure conditions, the mechanical part has been studied. Finite element analysis (FEA) simulation results show that the instrument maintains its mechanical integrity under high temperature and pressure (175 ℃, 30,000psi). The Monte Carlo N-Particle Transport Code System (MCNP) was used to verify the effect of the detector package on instrument response and neutron porosity measurements. Simulation results show that the new detector shell has minimal effect on neutron porosity measurements within the standard porosity measurement range. In addition, based on a large number of simulation results at different temperatures, a new temperature correction algorithm for neutron porosity measurement has been developed. Especially when logging temperature is very high, the algorithm is more accurate than currently used. The background subtraction algorithm has been fine tuned for high noise levels at high temperatures. The limestone, sandstone and dolomite formations, saturated with water of varying porosity and borehole size, were calibrated and characterized throughout the laboratory using upgraded instrumentation. The experimental results show that there is a good agreement between the instrument readings and the accepted laboratory porosity of the formation.