关键词: 花岗岩, 风化壳储层, 动态成因模式, 分布模式, 东营凹陷

Abstract: With the continuous discovery of granite reservoirs at home and abroad, granitic weathering crust reservoir have attracted more and more attention. Predecessors have done a lot of basic researches on the geological characteristics and reservoir features of granitic weathering crust. However, there is less research on the formation and evolution process of granitic weathering crust, as well as its transformation and preservation. Aiming at the problems about the formation mechanism and distribution regularity of granitic weathering crust reservoirs, based on the borehole core observation, rock thin section analysis, field outcrop survey, logging curve analysis and comprehensive seismic reflection interpretation on granitic weathering crust reservoirs, this paper systematically explores the dynamic mechanism of the formation, transformation and preservation of granitic weathering crust reservoirs, and obtains the following main understandings. (1) This paper proposes the dynamic genetic pattern of the "double-decker texture" of granitic weathering crust. It is considered that the weathering crust reservoir is composed of two layers, the top eluvium or dissolution layer and the bottom disintegration layer. As the same interval, the dissolution layer and the eluvium are actually the products of the top surface of the disintegration layer in different stages of evolution. In the early evolution of the weathering crust, the disintegration layer began to develop into a dissolution layer, and a double-decker texture with dissolution layer and disintegration layer appeared; in the middle-stage evolution of the weathering crust, the dissolution layer evolved into an eluvium, forming a double-decker texture with eluvium and disintegration layer. In the late evolution of the weathering crust, only the disintegration layer was preserved. (2) It is pointed out that the granitic weathering crust reservoir has undergone structural tilting, fracture destruction, fluvial abrasion and other transformation effects when it is formed, and it is believed that the preservation effect brought by the later stratigraphic coverage is crucial to the granite weathering crust. The earlier the later stratigraphic coverage occurs, the better it is for the preservation of granitic weathering crust reservoirs. (3) It is believed that there is a huge difference in the types of weathering crust on different elevations, different slopes and different structural belts. Only disintegration layers are developed at the top of the structure, eluvia are developed in the marginal areas of the high structural part, and dissolution layers are developed in middle-low structural parts. The disintegration layer is widely distributed. (4) This paper clarifies the exploration direction for the favorable reservoirs of granitic weathering crust, and believes that the development zone of dissolution layer preserved in the structural middle-lower parts are the most favorable development zones of reservoirs. The proposed dynamic genetic model of the double-decker texture of granitic weathering crust and the formation-transformation-preservation mechanism of weathering crust reservoirs have important reference significance for understanding the geological origin and exploiting hydrocarbon resources in granitic weathering crust reservoirs in other related basins.

Key words: granite, weathering crust reservoir, dynamic genetic model, distribution model, Dongying sag