A Method of Reservoir Connectivity Analysis for Single- and Dual-Porosity/Dual-Permeability Models
Authors: Madalimov Medet , Li Dachang , Saifutdinov Raif , Satybaldiyev Yernaz 
Published: October 2023

Reservoir connectivity analysis (RCA) is routinely performed in reservoir modeling/simulation, but its scope is limited by existing tools. Reservoir simulation is too expensive to do RCA at geologic scale while streamline simulation works only for single permeability models. This paper presents a game-change method for RCA that is capable to analyze geologic/dynamic models with 106 ~ 109 cells in a matter of seconds or minutes using a regular PC for single- and dual-porosity/dual-permeability models. Using the graph theory, a 3D model with single- or dual-porosity/dual-permeability is converted into a graph with nodes and connections. Local fluid travel time proxies are calculated from reservoir rock/fluid properties and assigned to each connection. Global fluid travel time proxies are generated using Dijkstra’s shortest path algorithm and calibrated with reservoir surveillance data, e.g., interference test, tracer flow simulation and PLTs etc. The calibrated fluid travel time proxies are applied to create connectivity map between wells, plumbing charts, swept volume, and vertical conformance at a given scale. Multiple geologic scenarios and their upscaled dynamic models are analyzed and compared.

The proposed method was successfully applied in a giant carbonate reservoir that consists of the matrix dominated platform and highly connected fractures/karst rim. Due to complex geology and high H2S content, a dual-permeability compositional model was created to model the compositional sour crude flow with 132 million geologic cells and 4 million dynamic cells. Performing RCA at the geologic scale is important but cannot be done using the company’s computing resources. In addition, the preservation of the reservoir connectivity of the fine-scale geologic model in the coarse-scale dynamic model cannot be confirmed easily. Using this novel method, the fluid travel time proxies from the fine-scale and coarse-scale models were effectively estimated and found to be strongly correlated with the field interference test, tracer flow and PLT measurements. As a result, a connectivity map between wells, plumbing charts, swept volumes, and vertical conformance can be created for the robust field development/optimization plans with plausible geologic scenarios and accurate static/dynamic models. The quality of upscaling from the fine-scale model to the coarse-scale model was checked and confirmed. Connectivity map was constructed to quantify and visualize the fastest flow paths between wells and plumbing charts were built in platform-rim regions to assess reservoir connectivity between geologic zones. Also, PLTs were matched without running expensive simulations.

The novelness of the proposed method for RCA is that it provides a tool that can reveal the detailed connectivity networks between wells, plumbing charts, swept volume, and vertical conformance at a very fine geologic scale using a regular desktop computer, which cannot be done effectively with any available commercial tools. It also, for the first time, gives a way to confirm the preservation of the reservoir connectivity from a fine-scale geologic model to its coarse-scale dynamic model.