A discussion on features of sedimentary composition of shallow water delta fades: Taking BZ25 - 1S oilfield as an example

Based on comprehensive analysis of various geologic data, it is believed that the major pay zones in Neocene Minghuazhen Fm in BZ25 - 1S oilfield are deposits of shallow water delta facies. The shallow water delta facies is further divided into four microfacies, including distributary channel, natural levee, avulsion and interdistribu-tary, according on core observation and electrofacies analysis. Laterally, distributary channel microfacies and natural levee microfacies lie between interdistributaries and sometimes avulsion microfacies are also developed outside natural levee microfacies. According to shapes of channels and mechanisms of deposition, distributary channel microfacies can be divided into bed load type and mix load type. The characteristics of these two types of distributary channels are introduced and compared. Determination of stage, type and distribution of distributary channel micro-faices is critical to prediction of favorable reservoirs and placement of well patterns.