Middle-deep Reservoir Characteristics Of Paleogene Of Shahejie Formation In Langgu Sag

Langgu Sag is the northernmost hydrocarbon-bearing sag in Jizhong depression,has higher degree of exploration.At present,the main exploration targets are hidden reservoirs in the middle-deep stratum.However,the heterogeneity of the middle-deep reservoirs is strong,hydrocarbon distribution is complex,increasing the difficulty of hydrocarbon exploration.Based on the basic theory of oil and gas reservoir geology,this paper uses the core observation,thin film identification and image analysis,mercury injection data,logging data,fluid inclusions analysis and other technical methods.Comparing to previous research results,the reservoirs characteristic of the Es3 and Es4 s of the Paleogene in the Langgu sag which the depth is over 2000 m have been studied,including petrological characteristics,physical characteristics,pore throat structure,reservoir space dstribution situation,reservoir control factors etc.The rock types of middle-deep reservoir rocks of the Paleogene Shahejie Formation in the Langgu sag are mainly composed of feldspar sandstone,lithic feldspar sandstone and feldspathic lithic sandstone.Debris maturity is low composition maturity and medium structure maturity.There are many types of cements in the porosity of the reservoir,the content is medium,the carbonate minerals are mainly calcite cement and clay minerals are mainly kaolinite.The specific content of interstitial material in different tectonic zones is different.The reservoir porosity of the Paleogene Shahejie Formation in the Langgu sag is dominated by mesoporous-low porosity,and the permeability type is characterized by very low permeability and ultra-low permeability.Physical properties of Liuquan-caojiawu structural belt is better than the other two tectonic belts,the reservoir physical properties of Es3 are better than those in the Es4 s.The reservoirs of the Shahejie Formation has three abnormal high porosity zones,respectively for 2400 ~ 2600 m,2750 ~ 3250 m and 3800 ~ 4500 m.According to the existing measured physical properties,logging data,mercury intrusion test data,combining with the domestic clastic reservoir porosity and permeability type classification criteria,the middle-deep reservoir of Paleogene of Shahejie Formation in the Langgu sag are divided into?,?(?a,?b),?,? class,reservoir physical properties in turn deteriorated.The reservoirs of Es4 s in the study area are mainly ? and ? reservoirs.The reservoirs in the sub of Es3 are mainly ?b and ? reservoirs.The reservoirs in the middle of Es3 are mainly ?b and ? reservoirs,also a small amount of class ?,?a reservoir.The good quality of the reservoir is mainly developed in the bottom of the lake fan,braided river delta front underwater distributary channel sand,shore shallow lake beach sand body.The reservoir development of Paleogene of Shahejie Formation in Langgu sag is affected by sedimentation,diagenesis,tectonism,hydrocarbon filling,abnormal high pressure and other factors.The Sedimentary action control sand body development.There is a coupling relationship between diagenetic evolution process and pore evolution.Tectonic action under the cracks improve the transport channel of the reservoir,magma activity baking superposition effect so that the oil generation threshold ahead and promote hydrocarbon generation.The early hydrocarbon filling slows down the formation of authigenic minerals,the intermixing of minerals,and inhibits the filling of late carbonate cements,thus protecting the primary pores and playing a positive role in the evolution of reservoir properties.The development of abnormal high pressure mainly protect and transform the reservoir properties.The sedimentary factors,the reservoir physical properties and the exploration status are predicted in the favorable reservoirs of the middle-deep reservoirs of Es3 and Es4 s in Langgu Sag.