Waterflooding Development Strategy Study for a Large Multi-layered Sandstone Reservoir

Abstract

Abstract M1 reservoir is a large multi-layered sandstone reservoir of deltaic environment with oil bearing area around 1500Km2. Sand bodies of M1 is influenced by fluvial, tide and wave, which results in great variations in sand bodies distribution, reservoir quality, vertical and lateral connectivity, etc. Furthermore, M1 is still under primary depletion and current reservoir pressure is around saturation pressure. So how to successfully conduct waterflooding and effectively develop this kinds of reservoirs are very important. Through detailed geological characterization and dynamic description, 4 reservoir types with different reservoir quality and connectivity are defined and classified. Then 3 equal-probability geological models for M1 are built, which stands for Upside model with good lateral and vertical connectivity, Expected model with medium connectivity and Downside model with poor connectivity. And optimized waterflooding development strategy for different reservoir types with different stacked styles are studied through reservoir simulation based on 3 sector models. The optimized development strategy includes pressure maintenance level, well pattern, well spacing, and perforation strategy. The results show that the optimized well pattern and well spacing for different reservoir types with different connectivity expectations are different. For reservoir Type A of good reservoir quality, 1000m well spacing with inversed 9-spot pattern is optimum for Upside, Expected and Downside models. But for Type C of poor reservoir quality, 1000m well spacing with inversed 9-spot pattern is optimum for Upside model, while 700m well spacing with 5-spot pattern is optimum for Expected model, and 500m well spacing with 5-spot pattern is optimum for Downside model. For M1 reservoir, because good quality reservoir Type A and Type B are mainly developed in the South part, 1000m well spacing with 5-spot pattern is recommended. While poor quality reservoir Type C and Type D are mainly developed in the North part of M1, 700m well spacing with 5-spot pattern is recommended for this area. For perforation strategy, all zones perforated for both producers and injectors are the optimum for 1000m inversed 9-spot pattern, and only Type C and Type D layers are perforated for the infilling producers of 700m well spacing pattern. This paper offers a waterflooding development strategy case study for deltaic sandstone reservoirs, which details the optimized development strategy for different reservoir types with different stacked styles and connectivity expectations. It also provides a methodology and reference case for engineers to develop other similar fields.