Abstract
The reservoir in different parts of buried-hill draping zone is often quite different, so it is of great significance to clarify the reservoir characteristics for exploration and development. Based on core, well logging, seismic data and production data, reservoir characteristics of oil layer Ⅱ in the lower second member of Dongying Formation of L oilfield, Bohai Bay Basin, offshore eastern China are systematically studied. Analyses of seismic facies, well-seismic combination, paleogeomorphology, and sedimentary characteristics are carried out. Sediment source supply, lake level and buried hill basement geomorphology all contribute to reservoir quality. The research suggests that the different parts of buried-hill draping zone can be divided into four types. Reservoir thickness and physical properties vary. The area where the provenance direction is consistent with the ancient valley direction is a favorable location for the development of high-quality reservoirs. Under the guidance of the results, oilfield production practices in L oilfield offshore China are successful. Knowledge gained from study of L oilfield has application to the development of other similar fields.
Highlights
In recent years, oil and gas fields of commercial value have been found in buried hills and overlying strata in various oil-bearing basins in China (Jin et al, 2019; Tong et al, 2017; Cui et al, 2018; Zhao et al, 2010; Liu et al, 2014; Dong et al, 2015)
Guided by the ascending cycle of regional base-level, the analyses of paleogeomorphology, seismic facies and well-section facies show that oil group II in the lower second member of Dongying Formation of the study area is a progressive braided river delta deposit under the background of lacustrine transgression, and that sedimentary distribution is affected by provenance, lake level and buried hill basement
Reservoir characteristics of the overlying strata in the buried-hill draping zone are controlled by paleogeomorphology, lake level change and provenance supply
Summary
Oil and gas fields of commercial value have been found in buried hills and overlying strata in various oil-bearing basins in China (Jin et al, 2019; Tong et al, 2017; Cui et al, 2018; Zhao et al, 2010; Liu et al, 2014; Dong et al, 2015). The structure, reservoir characteristics and reservoir-forming mechanics of such buried hills and their overlying strata have become a research hotspot (Zhao et al, 2010; Wang et al, 2017; Luo et al, 2008; Ma, 2004). The reserves of Dongying braided-river delta sandstones in the buried-hill draping zone remain untapped in recent years. In order to guide the efficient utilization of the reserves in the buried-hill draping zone of Bohai L oilfield, it is necessary to combine the existing data to study the sedimentary reservoir, establish the sedimentary evolution model and make a fine prediction of the reservoir. Based on the sedimentary characteristics of oil layer II in the lower second member of Dongying Formation of Bohai L oilfield, this paper analyzes the sedimentary evolution through fine paleogeomorphology analysis and guides the efficient exploration of untapped areas
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