The Use of MIDST, an Expert System Building Tool for Solving Geological Problems

Abstract

Many geological problems can be solved using knowledge-based approaches, but system design is slowed by complex interactions that occur between knowledge engineers and geological experts. MIDST, a user-friendly set of tools, partially circumvents knowledge engineers and allows expert geologists to build expert systems directly. These tools address: (1) knowledge acquisition, and (2) knowledge refinement and updating. MIDST is a general purpose tool, and its application is demonstrated with the development of a system for characterizing fields, plays, and prospects (PLAYMAKER). Knowledge acquisition is driven by a graphic outliner which creates a conceptual hierarchical structure of nodes that defines the problem-solving domain (in this case field characterization). The user defines relevant geological classes and concepts (e.g., reservoir qualities, porosity and permeability, depositional setting, and facies), and provides relationships between nodal concepts as directed inferential links (e.g., depositional setting is linked to facies, and so to porosity and permeability). Next, a rule-editor is used to formulate rules that define links. Inferencing requires starting with low-level node characters in the conceptual structure (e.g., basin setting), and using results from these characters to successively infer characteristics at higher level nodes (e.g., porosity and permeability). Nodes can be created and removed, and links changed asmore » rules are developed. The knowledge refinement tool enables expert geologists to evaluate the effectiveness of expert systems by identifying deficiencies in rules when consultation results are unsatisfactory. This can be attributed to either incomplete rules, inconsistency between rule pairs, or lack of fine tuning in rule weights.« less