Induced Polarization Effects Associated With Hydrocarbon Accumulations: Minimization and Evaluation of Cultural Influences

The use of induced polarization (IP) methods in oil and gas exploration dates back to the 1930s, but the validity of anomalies has been difficult to establish. Although recent geochemical and downhole research has verified the source of IP anomalies in some geologic environments, the influence of cultural (anthropogenic) features on the electrical data remains a serious stumbling block to the acceptance of electrical methods in oil exploration. Spurious effects from power lines, pipelines, fences, and well casings can be misinterpreted as anomalies from hydrocarbon alteration or can mask true alteration anomalies. The cultural problem is not insurmountable, however, and it is not valid to assume automatically that all IP anomalies measured over oil fields are the result of culture. A case study of the development of an oil field near Post, Texas, illustrates how proper survey design can be used to minimize and evaluate the effects of culture in the interpretation of IP survey data. Evaluation of before-and-after IP data sets and two-dimensional finite element modeling strongly support the interpretation that the observed IP anomaly results from hydrocarbon-induced alteration and not from well casing or other cultural effects. Furthermore, the interpreted extent of the IP anomaly as defined in 1982 agrees well with the productive limits of the field as it exists more than 12 years later.