A New Method for Modeling Braided River Delta Reservoirs Based on Sequential Gaussian Simulation Controlled by Paleogeomorphic Parameters

Braided river delta is a crucial target for oil development. However, its geological modeling has been challenging due to its highly complex and changeable geometric morphological characteristics, as well as the rapid thickness changes caused by erosion and deposition. The strong heterogeneity and unique shape of braided river delta present additional modeling difficulties. Geostatistics sequential modeling algorithm can accurately represent well data but fails to reflect the delta complex shape. Sedimentary forward modeling can simulate the delta intricate shape better but struggles with fidelity to the well data. To address these challenges, this study proposes an improved sequential Gaussian simulation that faithfully simulates well data while accurately reproducing the shape of braided river delta. The formation of braided river delta was controlled by paleotopography. Our proposed modeling method combines the advantages of sequential simulation, which ensures well data accuracy, and draws from the idea of paleotopography controlling flow movement in sedimentary forward simulation. Our method includes the following steps: (1) Building a 3D paleotopography map of the target formation. (2) Calculating the slope direction at each grid cell position of 3D paleotopography map. (3) Using sequential Gaussian simulation based on well points thickness to simulate the thickness variation in the 3D space. (4) SGS will randomly select a grid cell to start the modeling based on variogram. The variogram needs define the major range direction which indicates slope direction. Setting the major range direction of the variogram for each grid cell to be consistent with the slope direction of the paleotopography at the same location. (5) Performing the above simulation steps on all grid cells to complete the modeling. The proposed modeling method is a significant advancement in accurately simulating the complex shape and predicting the thickness distribution of braided river deltas. The proposed method is predominately controlled by the well data, stochastic, and reproduces the intricate shape of braided river delta. In Bohai C Oilfield, the simulated Facies distribution and thickness variations properties are the main output for the study. Hence, In Bohai C Oilfield, the development plan and drilling activities were guided and implemented based on the study results. This method is easy to popularize and apply, making it valuable for thickness prediction and reservoir modeling in braided river deltas.