An intelligent recognition method of deep shale gas reservoir laminaset based on laminaset clustering and R-L-M algorithm

Abstract

Lamina structures, as typical sedimentary features in shale formations, determine both the quality of shale reservoirs and fracturing effects. In this study, through electric imaging logging, based on core scanning photos, thin sections, and other data from the Wufeng-Longmaxi Formation shale reservoirs in the western Sichuan Block, the characteristics and classification scheme of deep shale gas reservoir laminaset were clarified. In addition, with core scale electrical images, the electrical imaging logging response characteristics of different types of laminaset were identified. Based on electrical imaging logging images, a laminaset clustering algorithm was designed to segment the laminaset and then Levenberg-Marquardt (L-M) algorithm was improved by introducing a random forest to obtain the R-L-M algorithm, which was used to extract key parameters of laminaset such as attitude, type, density, and thickness. The average accuracy, recall rate, and F1 score of laminaset recognition results of this algorithm were 14.82 % higher than those of a well-known international commercial software (T). This method was used to evaluate the Longmaxi Formation shale gas reservoir in the western Sichuan Block. The development density of clay-siliceous (organic-lean) laminaset from the Longyi 1–4 small layer to the lower Wufeng Formation firstly decreased and then increased and the minimum value was found in Longyi 1-1 small layer. In contrast, the development density of siliceous-clay laminaset (organic-rich) first increased and then gradually decreased and the maximum value was found in Longyi 1-1 small layer. The clay-siliceous laminaset (organic matters-contained) and the calcareous-clay laminaset (organic matters-contained) showed a stable developmental trend.