Analyzing sediment accumulation rates of the upper cretaceous Sarvak Formation based on well logging data in a cyclostratigraphic framework, southwestern Zagros Basin, Iran

Abstract

Carbonate Sarvak Formation is considered as one of the productive oil reservoir units in Dezful embayment of the Zagros Basin. The current study focuses on the cyclostratigraphic analysis of the Sarvak Formation by using evolutionary spectral analysis approaches of fast Fourier transform (FFT) spectrogram combined with wavelet transform (WT) scalogram and multi-Taper Method (MTM) periodogram. The Multi-Taper Method (MTM) periodogram utilized in this study to detect the Milankovitch cycles in the Sarvak Formation. In addition, the power spectrum of spectral gamma-ray and formation density (RHOB) logs, based on evolutionary FFT and WT Scalograms indicate strong astronomical signals of the Milankovitch cycles (E, e, O, P) in three wells of the Anaran block. Using the new approaches of evolutionary correlation coefficient and evolutionary significance levels, variations in sediment accumulation rates during deposition of the Sarvak Formation were compared in wells A-C. The minimum and maximum amount of sediment accumulation in the upper Sarvak Formation in the studied wells are estimated to be approximately 2 cm/kyr and 5.2 cm/kyr, respectively. According to spectral powers observed in the evolutionary correlation coefficient spectrogram, the sedimentation of the upper Sarvak Formation in well C was mostly influenced by the long-eccentricity cycle (E); on the contrary and based on the observed spectral powers, the sedimentation of the upper Sarvak Formation in wells A and B is mostly influenced by Obliquity (O) and long-eccentricity cycle (E). The contribution of other cycles is insignificant compared to E and O.