CLARİFİCATİON OF STRUCTURAL AND TECTONİC FEATURES İN COMPLEX DEPOSİTS (ON THE EXAMPLE OF GURGAN-DENİZ FİELD)
Authors: Sarvan Heydarli Sarvan Heydarli 
Published: January 2022

The article is devoted to the clarification of the structural and tectonic structure of newly drilled wells in the Gurgan offshore field, which has been under development for a long time.The Gurgan-Deniz field, located in the Caspian Sea, has sufficient residual reserves. The Gurgan-Deniz field was discovered in 1947. In the same year, well No. 7 drilled in the south-western wing was put into operation. The depth of the sea is between 0.5-8 meters. The average depth is 2.5 m. From the material and technical point of view, the mines are supplied by Pirallahi Island, which is connected to it by dams 1.7 km to the east. Pirallahi Island is connected to Baku by rail and highway. The area is protected from winds and waves by the island from the west and northwest. The average annual sea temperature is +14 ºC, ranging from +2 to + 25.4ºC. In summer, this price is + 30-35ºC.
The geological section of the Gurgan-Deniz field has been studied and the following results have been obtained. Surakhani, Sabunchu and Balakhani strata participate in the upper part of the productive layer. The Surakhani stratum consists of clays and fine-grained sands. The thickness is 310 m. The Sabunchu stratum consists of alternating fine-grained sands and clays. The thickness is 400 m. The Balakhani stratum consists of lithological clay and fine-grained sands. The total thickness of the group is 620 m.
Post-Kirmaky Clay Suite is composed of clayey lithofacies. The thickness of the group is 127 m.
Post-Kirmaky Sand Suite consists of sandy lithofasis and clay intermediate layers. The thickness is 40 m.
The sediments of the Girmaki stratum, as in other fields of the Absheron oil and gas region, consist of alternating lithological composition of sandstone, thin and fine-grained sand and clay. Oily sandstones predominate here. The sandiness of the section increases from the ceiling to the heel. The layer divides into 3 oil halves. The total thickness of the formation is 273 m.
It has been established from the data of six wells drilled with a small number of wells in the north-western wing that this group is composed of high carbonate dense rocks. In the south-western wing, the PG formation is oily and has a total thickness of 140 m.
The sediments of the Qala formation has been opened by numerous wells in the south-western wing. The clusters has taken the form of a lens-shaped lithological field.
The field's reserves were first calculated and approved in 1949. According to well data drilled to clarify its boundaries, in 1951 the Oil Expedition calculated only the recoverable oil and gas reserves.
Oil and gas reserves were recalculated in 1974 and approved by the State Reserve Commission of the former Soviet Union in 1976.
In 1995, the oil and gas reserves of the Gurgan-Deniz field were recalculated by the SeaOilGasProject Institute (Oil and Gas Mining Geology Laboratory). When re-specifying the geological structure on the basis of analysis and processing of data collected in the course of the research, the following was taken into account:
The main objects are GS, PG and GaS. These strata are in turn divided into several horizons. The cut layer group is divided into GStop and GSbot parts. The upper part is not oily and the upper part is oily. GStop is divided into GS1, GS2 and GS3 horizons. PG layer complex is divided into PG1, PG2 and PG3 horizons. In the field, the Gala layer is supported by logs divided into 4-6 horizons. It is a structurally complex anticline. The reason for the complication is the presence of thrust. In addition, the thrust is in the direction of field. There are 3 transverse fractures. New wells have been drilled in recent years. With these wells, the structure of the field has been redefined. Correlation schemes and geological profiles have been established with the participation of new wells. Stratigraphic boundaries were determined based on the correlation scheme. New wells were compared with wells drilled in previous years. It has been revealed that there are innovations. The results were confirmed by geological profiles. A transverse and longitudinal geological profile has been compiled. New wells are involved in the profiles. The existence of №3a fault in the transverse geological profile has been proved. The amplitude of the fracture is between 90-110 m. In addition, it is located in subthrust. Fracture №3a was first given on the basis of our study. The longitudinal fracture, which divides the field into two parts (subthrust and above thrust), is observed in the geological profile. The amplitude of the thrust is 1000-1200 m. According to the new wells in the field, a number of structural changes and stratigraphic innovations have been achieved in the subthrust. All the obtained results were proved by correlation and geological profiles, structural maps were compiled for the ceiling of GS, PG and GaS.
Keywords: field, structural map, well, geological profile, correlation scheme, subthrust, fault.