Design and construction of the knowledge base system for geological outfield cavities classifications: An example of the fracture-cavity reservoir outfield in Tarim basin, NW China

Abstract

Tahe oilfield, located in NW Tarim Basin, is one of the largest and most difficult fracture cavity reservoirs in the world. Different fracture cavities, different generated mechanisms, and different oil production capacities. In order to study the significant parameters that can characterize the categories of facture-cavity. This research adopted outfield manual measurement, 3D digital modeling technique to obtain characterization parameters. According to experienced geological survey, typical outcrops were selected, then scanned by UAV (Unmanned aerial vehicle). Consequently, 3D digital models, including real coordinates and parameter information, were established by Agisoft Photoscan. Through geological testing results, various combination characteristic patterns of relative categories were analyzed. By using digital measure tool, combined with manually measured data, the parameters were extracted from the 3D digital model (DM). Then an initial geological database was established. For furtherly analyzing the database, the mathematic statistics methods of multiple linear regression (MLR), neural network technique (NNT) and discriminative classification technique (DCT) were applied. Using software of SPSS statistics 17.0, more than 200 groups of geological data (various categories of fracture-cavity) were optimally processed. Consequently, the significant characteristic parameters were interpreted to determine diverse categories. The results showed that: (1) cavity width, height, fracture length and cavity aspect ratio were significant parameters to classify runoff cavity categories. (2) Fault-controlled cavities could be accurately classified by fracture length and fracture density. (3) The main cavity categories could be distinguished by cavity width, cavity height and fracture density. Performances of the approach have been examined with 10 percentages of the samples, and a good agreement performed in the simulated results, and anastomosis rate was more than 80%. The researched results have critical guiding significance to evaluate types of fracture-cavity, develop and explore of fracture-cavity reservoirs. The construction technique of knowledge base can be applied for diverse fracture-cavity reservoirs in the various formations in different areas in the world.