Abstract:

As an important and special type of sedimentary system, deep-water gravity flow deposits have been widely studied since its discovery, and have been given increasingly more attention in the oil and gas exploration industry. Deep-water gravity flow system is developed in the Middle Member 3 of the Paleogene Shahejie Formation in the Dongying depression. We finely described the types and characteristics of deep-water gravity flow deposits, and the development and evolution in different sequences in the Shi 112 block (Haojia Oilfield), according to the seismic and core logging data. The gravity flow deposition pattern in this area is summarized, which provides an important reference for reservoir prediction in the developed wellblock. This study shows that the local deep-water gravity flow system is developed in the highstand system tract of third-order sequence, which comprises four fourth-order sequences ($\mathrm{SQQ}_{1-4}^{3}$) from bottom to top. The deep-water gravity flow deposits developed three major sedimentary types: slump, debris flow and turbidity current deposits. Furthermore, 12 types of lithofacies are identified. The gravity flow scale was relatively small in the $\mathrm{SQQ}_{3}^{2}$ period, but expanded in the $\mathrm{SQQ}_{3}^{3}$ period with the Dongying delta progressing towards the lake basin center. Slump deposits developed mainly at the deltaic front or the root of pro-delta slope, while sandy debris flow deposits were developed at the front of the slump deposits. Debris flow may have transformed to turbidites gradually during its forward transportation process. The turbidity current and debris flow in the deltaic front and pro-delta represent favorable sites for reservoir exploration in the developed wellblock.

Key words: deep-water gravity flow, slump deposits, debris flow deposits, turbidity current deposits, Dongying depression