Diagenetic facies identification and distribution prediction of Jurassic ultra-deep tight sandstone reservoirs in Yongjin Oilfield， Junggar Basin

Abstract

Deep-buried tight sandstone reservoirs have strong heterogeneity and complex distribution patterns， which makes it difficult to predict geological sweet spots in those reservoirs. In order to achieve efficient exploration and development， it is urgent to research the accurate identification and prediction of the diagenetic facies of reservoirs among the wells. The identification and distribution prediction of diagenetic facies were carried out using core， well logging， and 3D seismic data based on the diagenesis of Jurassic ultra-deep reservoirs in Yongjin Oilfield， Junggar Basin. It was considered that the diagenesis types of reservoirs mainly include compaction， cementation， dissolution， and metasomatism， which can be divided into five diagenetic facies， such as strong dissolution with chlorite enclave， medium dissolution with authigenic kaolinite， medium calcareous cemented dissolution， strong calcareous cementation， and strongly tight compaction. Based on logging data， petrophysical and physical parameters were used to identify diagenetic facies types of the reservoirs and determine their vertical distribution. The results find that the two dominant diagenetic facies， namely strong dissolution with chlorite enclave and medium dissolution with authigenic kaolinite， are mainly located in the sand body of the main distributary channel of the delta， with suitable reservoir property， and they are the main parts of the oil reservoir development. Based on the analysis of the corresponding relationship between diagenetic facies and seismic P-wave impedance， it is found that the P-wave impedance of the dominant diagenetic facies is relatively low， and the distribution of the dominant diagenetic facies can be predicted by the numerical distribution characteristics of P-wave impedance. Therefore， diagenetic facies distribution is predicted using the inversion results of 3D seismic P-wave impedance， and the development area of the dominant diagenetic facies is determined according to the corresponding relationship between P-wave impedance and different types of diagenetic rocks. The result indicates that the dominant diagenetic facies are mainly located in the Y301-Y302 well area in the northeast of the study area and the Y1 well area in the northwest， showing a locally continuous distribution pattern. Identification of diagenetic facies in reservoirs can provide an essential basis for the distribution prediction of ultra-deep geological sweet spots.

Keywords

• tight sandstone reservoir
• diagenetic facies
• diagenesis
• yongjin oilfield
• junggar basin