Development law of gravity flow sandstone reservoir in the second Member of the Dongying Formation in the northeastern Nanpu Depression

Abstract

With the improvement of hydrocarbon exploration, turbidite reservoirs formed by deep-water gravity flow have become an important target for oil and gas exploration and development in faulted basins in eastern China. Due to the weak depositional differentiation and diagenesis damage, the overall quality of gravity flow sandstone reservoirs is poor. The prediction of high-quality reservoirs is becoming the key to restricting effective hydrocarbon exploration. In this paper, the authors study the distribution, lithofacies, and reservoir characteristics of gravity flow sandstone in the northeastern Nanpu Depression by cores, well-logging data, reservoir physical properties, and rock slices to explore the key control factor and development law of high-quality reservoirs. The result shows that the gravity flow sediments are mainly composed of eight lithofacies interpreted as slide-slump, sandy debris flow, muddy debris flow, and turbidity current. According to the statistical analyses of reservoir physical property parameters, it is proven that the gravity flow sandstone reservoir is with strong heterogeneity and that its quality depends on sandstone genesis, sand-mud structure, and dissolution intensity. The high-quality reservoirs are mainly from sandy debris flows and turbidity currents. Massive sandstones from sandy debris flows are usually high-quality reservoirs characterized by large single-bed thickness, strong calcareous dissolution of calcareous cement, and few muddy interbeds.In contrast, the sandstones from turbidity currents are of low quality due to small thickness, weak dissolution of calcareous cement, and many interbedded mudstones, and are formed in a closed diagenetic environment. This study provides an effective predictive idea for hydrocarbon exploration on deep-water gravity flow sandstone reservoir in a lacustrine basin based on analyses of sandstone genesis and sand-mud structure.

Keywords

• sediment gravity flow
• sandstone reservoir
• debris flow
• turbidity current
• sand-mud structure