The Formation Mechanism And Reservoir Accumulation Characteristics Of The Salt-eave Structure In The D Block Of The Precaspian Basin

The Precaspian Basin extends from the east to the west, which is1000km long, and the largest width is650km.The figure of the basin is an oval, and the area of it is54.2×104km2.The largest deposition thickness is more than20km, which is the largest and the deepest area in the Russian platform, and it is also one of the deepest basin in the world. Administrative divisions,85%of the total basin area of the Republic of Kazakhstan, and the remaining15%belongs to Russia.The Precaspian Basin has rich oil and gas resources. According to data reported, the basin had proven272×108tons reserves, and it has found more than200fields, and it is the main oil and gas producing area in Kazakhstan, and it is also one of the important oil and gas producing areas in Russia.The depth of the Precaspian basin basement varies greatly. According to the shape of the substrate structural top, the basin is divided into four major tectonic units, north and northwest fault zone, central depression zone, Astrakhan-Actobe uplift zone and the southeast depression zone.D block is located at the east side of the central depression zone and the Astrakhan-Aktobe uplift zone in the eastern part of the Precaspian Basin. It had found11small-medium-sized fields in the block, and it is a favorable area for the oil and gas accumulation.Salt-eave structure is a new structural model summarizes by the exploration research work in D block, and the concept of the structural model derived from its shape and structural positions. Salt-eave structure is a fault-anticline or fault-nose structure on top of a flank of the salt. Salt-eave structural reservoir is common in D block. Currently, there are a lot of salt-eave structures with oil and gas discovered in D block. With the exploration strategy changes, salt-eave structure as the main exploration targets. Strengthen the research of this new structural reservoir’s characteristics will be an important guiding significance for the oil and gas exploration work in D block.Based on collecting the data of geophysical prospecting, drilling, logging, mud logging,core laboratory and the exploration results analysis in D block, in order to describe the trap characteristics of salt-eave structure, and analyze the causes of the oil reservoir characteristics, the conditions of its oil resources, oil and gas migration conditions and reservoir conditions. Analysis the forming elements of the reservoir, and summary of the salt-eaves structural reservoir forming characteristics.The studies suggest that:1.The salt-eave structures is developed in the Middle Triassic strata attached to the top of the salt constructed attached to the salt bodies. It’s a new type concept which describes the structure position and its relative to the salt bodies,and the structure type may be anticline, faulted anticline and fault block.2.Based on the classification of the salt-eave structures have been drilled in D block, it mainly develops three types of traps:①The salt-eave anticline or faulted anticline traps;②The salt-eave faulted nose or faulted block traps;③The salt-eave unconformity traps;3.Contrast with the other post-salt structures, the salt-eave structure has more favorable accumulation conditions:The spatial location of the structure is located in a favorable hydrocarbon accumulation; The salt-eaves structure constructed with better preservation conditions; It has various types of traps,and the traps buried moderate.4.The master factors for the reservoir constructed of the salt-eave structure:The effective salt windows are the necessary conditions for the accumulation of salt eaves; Good preservation conditions is the key to constructing reservoirs.