Hydrocarbon Reservoir Formation Mechanism Amd Pattern For Saline Series In Wenliu Area, Dongpu Depression

Wenliu area is one of the primary areas for salt to distribute in the north of Dongpu depression. Exploration has proved that salt development has a primary effect in hydrocarbon formation. On the basis of previous research, this article has made full use of newest methods and techniques and theorys for hydrocarbon formation and reservoir formation such as confined space experimental modeling technique to conduct research on hydrocarbon formation mechanism of source rock, hydrocarbon migration mechanism, preservation mechanism and reservoir formation mechanism for salt lake environment in Wenliu area and has generalized reservoir formation pattern as well, which plays an important role in guiding further exploration in this area.Through comprehensive study on organic abundance, its type, sedimentary environment, generative characteristic and so on, source rock of Dongpu depression is divided into three types: good-high quality source rock in north salt area, medium-good source rock in north non-saline area and poor-medium source rock in south non-saline area. Abundant dinoflagellate fossils have been found in strata in salt area, available for preservation with high organic abundance and good type. Hydrocarbon generation and expulsion model has been built for limnic mudstone in north salt area and south non-saline area by using confined space experimental modeling technique. It has been determined that hydrocarbon potential of limnic mudstone in salt area is obviously higher than that of non-saline area and entered into hydrocarbon generation peak earlier. Critical pressure difference (3MPa) of effective longer distance migration for oil and gas obtained by simulated experiment is a great contribution for hydrocarbon reservoir formation study.By study on relation between therobaric field and hydrocarbon migration and distribution in Wenliu area and combined with oil sources correlation and transforming system study, hydrocarbon migration and accumulation unit in Wenliu area is divided into 4 subunits: Wendong hydrocarbon migration and accumulation subunit, Wenzhong hydrocarbon migration and accumulation subunit, Wenxi hydrocarbon migration and accumulation subunit, Wennan-Liuzhuang hydrocarbon migration and accumulation subunit, each of which shows different characteristic for hydrocarbon reservoir formation.Cap rock and reservoir bed are closely related with salt development in Wenliu area. As good regional cap rock, breakthrough pressure of salt is generally more than 20MPa. Abnormal pressure formed by salt development can slow down compaction apparently, restrain cementation, accelerate denudation and formation of mudstone and sandstone fissures, favorable for improving petrophysical property of deep reservoir bed.Study on essential factors of reservoir formation has helped to build up dynamic procedure of reservoir formation in salt lake environment and reservoir formation mechanism has been made definite. Three main stages for reservoir formation have different characteristics: during S2-Dongying depostional stage, C-P coal measure source rock was primary gas source rock and sub-salt Wen23 reservoir formed in top central uplift. Dongying movement stage was scale migration and accumulation stage for oil and gas. S3 source rock was taken as basis and reservoir mainly formed at structure high. During Guantao formation-present depositional stage, fault closure became better and reservoir mainly formed at structure low. Inhibition for reservoir formation produced by abnormal pressure caused generation of plenty of oil and gas in later period of soure rock, providing material base for reservoir formation in structural low. New view that reservoir formed in later period at structural low has provided theoretical basis for potential exploration of structural low.Based on reservoir formation mechanism study, there are four patterns of reservoir formation classified for Wenliu area:â‘ Wendong mix-sourced, multi stage, fault-sand body-salt controlled pattern,â‘¡Wenxi mix-sourced, multi stage, fault pattern,â‘¢Wenzhong out-sourced, single stage, fault-sand body pattern,â‘£Wennan-Liuzhuang mix-sourced, multi stage, fault-sand body pattern. The four patterns have different characteristics for hydrocarbon accumulation, which will be helpful for guiding exploration in corresponding area.