Detection and Classification of High-frequency Cycles in the S3 Sand Member of Shanshan Oil Field, Xinjiang
QIU Yubo1, YI Haisheng1,2, ZHANG Jun3, WEN Jun1, WU Chihua1
1. Institute of Sedimentary Geology, Chengdu University of Technology, Chengdu 610059, China;2. State Key Laboratory of Oil and Gas Reservoir Geology and Exploitation; Chengdu University of Technology, Chengdu 610059, China;3. Tuha Oilfield Company, Shanshan Oil Production Plant, China National Petroleum Corporation, Shanshan 838202, Xinjiang Uygur Autonomous Region, China
Abstract：In an oilfield, the sublayers, sedimented at the same time, are the elementary units of its oil/gas development, as well as the main body of the sedimentary cycles of the reservoir bed. In the classification and correlation of sublayers, a sand body in the reservoir is usually taken as the reference. But the distribution of sand bodies in a strata space is often variable, which increases the uncertainty of the classification of sublayers. In this paper, the natural GR curves are used and the method of the evolutive spectral analysis is applied. Through the comparative analysis of several wells in Shanshan oil field, 6 cycle boundaries and 5 high-frequency cycles are identified in the S3 Sand Member of Sanjianfang Formation. The appearance of cycle boundaries is consistent with the abrupt interface of the cyclic wavelength peak in the frequency spectrum. The cyclic wavelength is found to be controlled by the sedimentation rate, but has not direct relation with the lithological change and the appearance of the sandbody. So this method can be used to deal with the classification of oil layers marked by lithology. The thicknesses of these cycles range between several meters and ten or more meters. They are very close to the cycle scale of a sublayer, and these cycle boundaries detected by an abrupt change of the sedimentation rate are isochronous in the regional geologic domain. These high-frequency cycles can also be laterally compared and be considered as an important geologic parameter and a criterion in the classification and the correlation of sublayers in the oilfield development.