Remote Sensing Enhancement And Interpretation Of Surface Hydrocarbon-induced Manifestation In Western Slope Zone Of Songliao Basin, China

Hydrocarbon leakage or migration would result in rock, soil and botanical anomaly in near-surface sediments which can be identified in remote sensing image. Because of its wide region, simple surface cover and promising deposit of heavy oil in Western slope zone of Songliao basin, China, the area is suitable for remote sensing study. The present study used ETM+ (Landsat 7 Enhanced Thematic Mapper Plus) image to identify the hydrocarbon-induced area based on the diagnostic spectral characteristics of the hydrocarbon-induced manifestations and the spectral enhancement including Principal Component Analysis (PCA), band ratioing, Optimum Index Factor (OIF) and False Color Composition (FCC). The optimum principal components, band ratios and false color compositions were achieved. According to the theoretical characteristics of hydrocarbon-induced manifestation and the tonal characteristics around the existed well, the hydrocarbon-induced area were interpreted in the whole area. Then, the identified tonal anomalies were discussed in the context of geochemical data and cross sections to validate the reliability of the result. The geological setting of the tonal anomaly was noted and the geochemical characteristic resulted from hydrocarbon leakage on the ground was priamaryly achieved. Geochemical measurement results of the samples from exploratory well and logging interpretation were used to imply the geochemical characteristic along with the vertical pathway of hydrocarbon migration. Main conclusions and developments of this study are listed below:1. In Western slope zone of Songliao basin, China, there are four principal components (PCs) have relatively good enhancement for delineating mineral and sediment anomalies caused by hydrocarbon leakage. And there are four band ratios have relatively good enhancement for delineating mineral and sediment anomalies caused by hydrocarbon leakage.2. The selected principal components and band ratios are used for statistical multi-bands combination analysis of OIF. Then according to the OIF result, five false color compositions have good representation of the hydrocarbon-induced manifestation. The interpretation result shows that the hydrocarbon-induced areas have steady distribution and were related close to geological setting.3. The geochemical measurements of ground samples indicated that the tonal anomalous area in remote sensing image is related close to soil chemistry changes: (1) The acidolysis hydrocarbon measurement of ground soil samples from the first-order promising area reveals that light hydrocarbon concentration is larger in the first-order promising area and the spatial distribution of light hydrocarbon concentrations mostly agrees with the distribution of the promising area. (2) the delta-carbonate test (ΔC) of ground soil samples from the first-order promising area indicates that the occurrence of anomalous concentrations of delta-carbonate is positive evidence for the tonal anomaly. (3) It is noted that the direction of the magnetic susceptibility is NNE, coincident with the anomalous area. Though the variation image can't cover the whole anomaly because of the limited distribution of the surface samples, it implies that the correlation between magnetic properties and the surface anomalies caused by hydrocarbon is positive in this area. (4) The result of the Ce/La ratio in the third-order promising area is low indicating the reducing environment. The positive spatial correlation between tonal anomaly and reducing environment emphasizes the idea the identified anomaly has a geochemical origin.4. The strata section crossing the first-order promising area (southern Fulaer'ji) indicates that the most drilling wells around this anomalous area have met the oil-bearing layer. However, the surface anomalous area detected in the remote sensing interpretation is smaller than that which might be inferred from the profile and is often located updip and westward of the reservoir. And it is may caused by the eastward strata and the spectral disturbance of city zone and Nen River.5. The magnetic susceptibility (MS) and delta-carbonate (ΔC) of rock samples in wells Jiang 75 and Jiang 76 show the geochemical characteristics along with pathway of hydrocarbon migration as below: (1) MS value of near surface sample is smaller than that of deep-seated sample and the delta-carbonate content of near surface samples is much higher than that of deep-seated sample. (2) Above the oil-bearing layer, the magnetic susceptibility of sandy gravel sample is increasing along with the decrease of the depth. In contrast, the delta-carbonate content is decreasing when the depth is decreasing. And the lowest MS and highestΔC perfectly mark oil-bearing layer of the oil shale. (3) MS value and delta-carbonate content have very large variation in sandy gravel samples and decrease strongly when the depth is decreasing. (4) Samples of near surface exhibit an intense variation of the delta-carbonate content and relatively steady representation of magnetic susceptibility.The result suggests that the enhancement and interpretation of remote sensing image for the study area proposed are applicable and dependable for the study area. The relationship between the many kinds of field data and identified anomalies from remote sensing image suggests that the hydrocarbon-induced manifestation would cause characteristics both on the ground and along with the vertical pathway.