The geological reservoir conditions of offshore fluvial oilfields in the Bohai region are characterized by their complexity, including thin reservoir layers, significant lateral variations, and poor connectivity. These conditions pose challenges in deploying production wells, finely describing reservoirs, and optimizing resource allocation. This study has developed several techniques to address these challenges effectively. These include fine description and quantitative characterization of reservoirs in areas with few wells, regional sedimentation analysis and identification of individual river reservoirs, optimization of well networks for single sand bodies, and a rolling technique for tapping potential in fluvial oilfields. The effectiveness of these techniques has been confirmed through their application in the development of 11 oilfields in Bohai, resulting in the addition of newly discovered reserves amounting to 5 billion tons during rolling development evaluations. The fine description technology has achieved a drilling accuracy rate of 98%, while the recognition technique for individual river reservoirs in fluvial environments has increased the recovery rate by an average of 3%. Moreover, the rolling development technique has enabled rapid resource transformation around the oilfields, facilitating the efficient development of oil and gas resources. The Bohai oilfield, situated in the Bohai Sea, is part of the offshore Bohai Bay Basin. After four decades of exploration and development, this field has produced significant oil reserves from the Neogene Minghuazhen and Guantao formations. In 2012, these reserves constituted 56.3% of the Bohai oilfield's total proven oil reserves, underscoring the critical role of efficient development strategies for these reservoirs in maintaining and enhancing oil production. These formations have undergone extensive fracturing due to recent tectonic activities, resulting in a highly broken structure and complex fault blocks. Post-Neogene, the Bohai Sea became a major drainage center for the Bohai Bay Basin, fostering not only traditional fluvial sedimentary systems but also shallow water delta systems, primarily around distributary channels or underwater channels. The fluvial oilfields discussed in this paper include reservoirs from both meandering and braided river systems, as well as parts of shallow water delta distributary channels. The reservoirs typically exhibit curved strip, ribbon, and dendritic shapes, and feature thin reservoir layers with substantial lateral variation. This complexity is further compounded by interactions between water and oil beds, leading to a distinct "one sand body, one oil reservoir" scenario. To effectively develop these fluvial oilfields, the research employs advanced techniques. These include detailed reservoir description and quantitative characterization in areas with sparse well distribution, study of regional sedimentary evolution and identification of individual river reservoirs, optimization of well networks for single sand bodies, and a rolling technique to tap potential in fluvial oilfields. These methods are essential for overcoming the geological challenges and optimizing oil extraction in such complex environments. The development of offshore fluvial oilfields encounters specific challenges, largely due to differences in the approach and conditions compared to onshore oil field development. For onshore fields in China, the development strategy typically evolves progressively, beginning with the establishment of a basic well pattern. This initial phase is followed by integrated geological and reservoir studies to determine optimal development and infill drilling patterns. In contrast, offshore oilfields are constrained by several factors that complicate their development. High operational costs limit the number of exploratory wells that can be drilled, resulting in sparse well patterns and consequently less data for making informed decisions. Additionally, the physical limitations of offshore platforms — such as available space, the lifespan of the platform, and finite well slot resources — prevent frequent adjustments to the drilling plan. To navigate these challenges and achieve efficient development, offshore oilfields require robust preliminary research. This involves a comprehensive and detailed geological description of the reservoirs, which forms the basis for strategic deployment of development wells. By adapting the well deployment strategy to the specific geological characteristics and constraints of offshore environments, developers can enhance the effectiveness and efficiency of oil extraction from these complex reservoirs. Keywords: geological reservoir condition, fluvial oilfields, geological challenges, seismic data, conventional method
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Nov 2, 2024
Shoucheng Xu + 5
Open Access
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