Lithofacies Types and Reservoir Characteristics of Mountain Shale in Wufeng Formation-Member 1 of Longmaxi Formation in the Complex Structural Area of Northern Yunnan–Guizhou

Abstract

The mountain shale in Wufeng Formation-Member 1 of Longmaxi Formation in the complex structural area of northern Yunnan−Guizhou has great potential for exploration and development. In order to clarify the differences of reservoir quality and the longitudinal distribution law of different lithofacies, the lithofacies in Wufeng Formation-Member 1 of Longmaxi Formation was divided combined with core, logging, and analytical test data. Based on the data of total organic carbon, laminate structure, reservoir porosity types and physical properties, and gas content, the reservoir characteristics and advantageous lithofacies shale reservoir distribution were determined. The results show that the mountain shale lithofacies in the study area are divided into 7 major types and 20 subtypes. The high-carbon siliceous shale has the highest degree of organic pore development, specific surface area (average 28.55 cm 2 /g), and pore volume (average 0.0397 cm 3 / g). Two types of advantageous lithofacies shale reservoir in the study area were identified. The high-carbon siliceous shale reservoir could be considered as an excellent shale reservoir for shale gas and is mainly concentrated in the first section. It is mainly developed in layer-1 and the bottom of layer-2 of the Longmaxi Formation, providing favorable source-reservoir conditions for shale gas enrichment. The medium-carbon siliceous shale, medium-carbon clay siliceous shale, and medium-carbon calcareous siliceous shale, developed in the top of layer-2 and the bottom of layer-3 of the Longmaxi Formation, are assumed to be moderately promising for shale gas. Therefore, the research results deepen the understanding of the longitudinal distribution of the dominant shale reservoirs in the study area and are of great significance in promoting strategic transfer of the main shale gas exploration system in the south from the Sichuan basin to the outer basin.

On the Pore Geometry and Structure Rock Typing

“…• Based on mechanical properties, mineralogy, and organic geochemistry 7 • The use of permeability, porosity, and irreducible water saturation data either empirically 5,8−10 or with a hydraulic flow unit (HFU) approach; 1,3,11 • Involvement of capillary pressure data and J-function 12−14 and combined with radius; 5 • Consideration of thin section descriptions and interpretations such as rock fabrics, 15 depositional facies, 16 and rock textures; 17,18 • Geostatistics and machine learning implementation such as clustering, 19,20 ANN, 21 self-organizing map, 22,23 and fuzzy logic; 24 • Grouping based on the dimensionless form of absolute permeability, relative permeability, porosity, and phase viscosity, the so-called true effective mobility TEM function; 25,26 • The use of resistivity data and porosity to yield in electrical flow unit; 27 • Further development of analytical models, such as the pore geometry and structure (PGS) method. 28−31 The PGS method is built on the basis of the Kozeny−Carman and capillary bundled model equations, ending up with a plot between y k/ and x � k/ϕ 3 within a power function y = ax b28, 29 such that The inspiration came from the facts that many physical phenomena in nature are in a power law scaling relationship.…”