应用激发极化、视电阻率和电磁感应法探测石油和天然气

为了探测石油和天然气,自从1977年以来,在电法方面进行了广泛的研究,提出了各自的有意义的结果,但其中有些是和石油工业界人士最近的调查结果不一致的。在逆掩断层带,帕拉道克斯盆地,温德河盆地,波德河盆地,盆地和山脉区,丹佛盆地和得克萨斯狭长地带等地区条件下所作的种种调查,得出了下列结果:所测得的真正的激发极化异常还不到我们在已知油气田上调查总数的30％,明显的视电阻率异常则占不到实例总数的60％。然而,如果从野外测量结果的总体中将激发极化和均匀大地的理论响应消除后,将测得的谱的剩余部分称作剩余电磁或REM资料,则它在92％的调查地区中给出了真实的与油气相关的异常。REM的穿透深度正比于趋肤深度,而视电阻率和激发极化法的穿透深度则决定于标准的电流传导深度,电子计算机数字模拟和野外测量结果都指示REM的最大有效穿透深度是偶极距的四倍到六倍。在犹他州圣胡安县,位于帕拉道克斯断层和褶皱区中的里斯本油田证明了是一个油气异常的好例子。生油层的平均深度是8500英尺,上覆的帕拉道克斯盐岩的厚度在3000到7000英尺之间变化,形成了一个特别有趣的探测目标。调查的结果同在其它油田上收集到的资料一致,即激发极化的资料是没有说服力的,电阻率资料显示了良好的异常,REM资料显示了与油气的

HYDROCARBON EXPLORATION USING INDUCED POLARIZATION, APPARENT RESISTIVITY AND ELECTROMAGNETIC SCATTERING

Extensive research since 1977 in electrical methods for hydrocarbon exploration has yielded several interesting results, some of which are inconsistent with recent findings by others in the industry. A variety of surveys in the Overthrust Belt, Paradox Basin, Wind River Basin, Powder River Basin, Basin and Range Province, Denver Basin and Texas: Panhandle environment has yielded the following results: bonafide polarization anomalies were measured in less than 30% of our surveys over known hydrocarbon accumulations, and apparent resistivity anomalies were evident in less than 60% of the cases. When ground polarization and the theoretical homogeneous earth response are separated from the total field measurement, however, the remaining portion of the spectrum, called residual electromagnetic or REM data, has shown bonafide, cor-relatable anomalies in 92% of the sites surveyed.The depth of penetration for REM data is proportional to skin depth, while standard galvanic depths of penetration apply to the apparent resistivity and induced polarization data. Both computer modeling and field measurements indicate that the maximum effective depth of penetration for REM data is four to six times the dipole spacing.The Lisbon Oil Field in too Panadox Fault and Fold Province in San, Juan County, Utah, proved to be a good example of hydrocarbon anomalies. Average production depth is 8500 feet, and a variation in thickness of the overlaying Paradox Salt from 3000 to 7000 feet made this a particularly interesting target. Survey results were consistent with data collected over other oilfields, i.e., polarization data were inconclusive resistivity data showed good anomalies, and REM data showed strong anomalies, well-correlated with the hydrocarbon reservoir.Electrical anomalies associated with hydrocarbon accumulations have been measured by a number of researchers, but the actual anomaly me-chanism(s) remains in question. The fact that induced polarization eff-ects are measured over some oilfields but not others, while conductive resistivity and REM anomalies are much more consistently found, suggests-that more than one anomaly mechanism is at work and that the mechanisms vary with geologv.