Low Permeability Reservoir Characteristics And Hydrocarbon Accumulation Of Quan4 Formation In Longxi Area

The low permeability reservoirs is becoming more and more important, as well as the mid-high permeability old fields entered mid-high water cut stage with the development of oil gas exploration. In this paper, the research centering on low permeability reservoir characteristics and hydrocarbon accumulation in Longxi area is made, based on comprehensive utilization of seismic, well logging, coring and analysis of testing data and multi-disciplinary theoretical and methodological techniques.On the basis research on characteristics of structure, deposition and diagenesis, low permeability sandstone reservoir characteristics and influencing factors of Quan4 Formation in Longxi area of Songliao basin are systematically studied. Sandstone composition and structure maturity are lower with obvious characteristics of low porosity and low permeability. The pore spaces are completely dominated by the residual intergrannular and intragrannular solution pores. The heterogeneity of pore structure is intense, and the pore throats are fine. Due to the lower composition maturity, compressive strength is weak, and compaction is strong. The low composition maturity are mainly responsible for poor reservoir properties. Dissolution of K-feldspar contributed a large amount of secondary porosity, is an important effective factor. The relation between reservoir properties and particle size is positive. Reservoir properties and particle uniform level is a positive correlation. Fine particle and poor uniformity of Quan4 Formation sandstone are the internal factors of low porosity and low permeability. The interstitial material fills the pore space, and makes pore structure complicate.The high content of interstitial material is one of the reasons of poor reservoir properties. Compaction and cementation makes primary porosity decreased, and the physical properties deteriorate.Dissolution improves the reservoir properties. Structure changes in environment of diagenesis mainly through the depth and fluid nature of the reservoir, and has an impact on reservoir properties. Base on main factors controlling on hydrocarbon pooling of Quan4 Formation in Longxi area of Songliao basin, oil and gas generated from hydrocarbon source rock of Qing1 formation mainly migrate into Quan4 Formation in two ways. one is oil and gas generated from hydrocarbon source rock of Qing1 formation migrate down along the faults into Quan4 Formation under the large below -souce pressure difference. The large below-souce pressure difference is up to abnormal pressure of Qing1 formation formed by compaction and hydrocarbon generation and negative pressure of Quan4 Formation generated along with fault activity. The other one is oil and gas generated from hydrocarbon source rock of Qing1 formation lateral migrate into Quan4 formation under the conditions of hydrocarbon source rock of Qing1 formation on the dumping direction lateral connection to Quan4 Formation formed by fault activity. The activity of Aogula-HaJahai faulted zone formed the regional syncline in its west, where is not conducive to migration and accumulation of oil and gas. The eastern area of Aogula-HaJahai faulted zone is slope, where is conductive to lateral migration of oil and gas. The activity of Aogula-HaJahai faulted zone formed the mudstone of Qingshankou lateral connection to the sanstone of Quan4 formation on the dumping direction in the west side of Aogula-HaJahai faulted zone, where is conducive to accumulation of oil and gas. A large number of fault-lithologic oil and gas pools formed in the eastern area of Aogula-HaJahai faulted zone.