Study on sedimentary architecture of single sand body in shallow water deltas based on dense well pattern and interwell tracer data： A case study of Es21 and Es22 in Shenger District of Shengtuo Oilfield， Dongying Sag

Abstract

Sand bodies in distributary channels and mouth bars of shallow water deltas are often distributed in continuous sheets， making it difficult to accurately classify the single sand body， limiting the accurate prediction of remaining oil distribution and restricting the further enhanced oil recovery （EOR）. Based on core， well logging， and other data， the characteristics of the sedimentary architectures of single sand bodies in shallow water deltas in the 1st Submember of the 2nd Member of the Eocene Shahejie Formation （Es21） and the 2nd Submember of 2nd Member of the Eocene Shahejie Formation （Es22） in Shenger District of Shengtuo Oilfield， Dongying Sag were systematically analyzed by using dense well pattern and interwell tracer data. The results show that shallow water delta deposits are developed in Es21 and Es22 in Shenger District of Shengtuo Oilfield， Dongying Sag， including plain subfacies and front subfacies of shallow water deltas. In addition， microfacies such as distributary channels， overbanks， mouth bars， and beach bars are developed. The sand bodies of shallow water deltas were divided into four architecture units （Levels 5-8）， and the single sand bodies in this study belong to the level-8 architecture unit. Six types of lateral contact patterns between single sand bodies were identified by comprehensively using dense well pattern and interwell tracer data： channel-overbank-channel splicing type， channel-channel cutting and stacking type， beach bar-beach bar splicing type， mouth bar-mouth bar splicing type， channel on dam cutting mouth bar type， and mudstone separating type. Interwell tracer data show that the sand body has the best connectivity in the channel on dam cutting mouth bar type， followed by channel-channel cutting and stacking type， mouth bar-mouth bar splicing type， and beach bar-beach bar splicing type. The worst connectivity is from the channel-overbank-channel splicing type. Finally， the sedimentary architecture models of single sand bodies in shallow water deltas in the study area were established. The microfacies type of the shallow water delta plain is mainly a distributary channel. The contact patterns between sand bodies in a single distributary channel mainly include lateral incising and overlapping， lateral contact with sand bodies on an overbank， vertical superposition， and oblique superposition. The microfacies types of sand bodies in the shallow water delta front are distributary channels， mouth bars， and beach bars. The contact patterns between sand bodies in a single mouth bar include vertical superposition， lateral splicing， oblique superposition， and mudstone separation. Two types of lateral splicing and vertical superposition exist between sand bodies in a single beach bar.

Keywords

• shallow water delta
• sand body architecture
• dense well pattern
• tracer
• dongying sag