Reservoir Characteristics Of Tuff Tight Oil Reservoirs In Ma 56 Block Of Santanghu Basin And Research On The Geological Mechanism Of Enhanced Oil Recovery

The tight oil reservoirs of the Permian Tiaohu Formation in the Malang Sag of the Santanghu Basin are different from other well-disclosed tight sandstone,shale and carbonate reservoirs,but are dense tuff reservoirs with sedimentary organic matter.Based on the research results of many predecessors,this paper is based on cuttings observation,drilling core,thin slice identification,scanning electron microscopy,mercury intrusion analysis,etc.,guided by multidisciplinary theory,using a variety of analytical methods as a means.The characteristics of the tuff-tight oil reservoirs and the enhanced oil recovery geological mechanism of the Ma 56 Block and Tiaohu Formation in the Santanghu Basin were systematically studied.The following results were obtained:(1)The development and sedimentary evolution characteristics of tuff in the Tiaohu Formation of Malang Sag are defined.From 1 to 3 layers in the second section of the Tiaohu Formation in the Malang Sag,the water body gradually becomes shallow,the sedimentary facies gradually transitions to the continental facies,the deep lake-semi-deep lake facies gradually shrinks,and the shallow lake facies and delta facies develop gradually.The comparison between the measured thickness of the well and the original stratum thickness shows that the tuff at the bottom of the second member of the strip is deposited in the low depression of the depression,and the tuff of the second member of the strip lake is distributed along the northwest-southeast direction,which is basically coincident with the original sedimentary thickness center of the second member.Ma 56 block is a relatively pure powder-micro-scale tuff.Under the scanning electron microscope,pyrite can be seen,and the thickness of tuff reaches 10~30m,showing a large area of continuous distribution.It is judged that the tuff of the Tiaohu Formation is erupting in the north and south.The formation of the near-source volcanic ash"airborne"water,its development is mainly controlled by the volcanic eruption and paleo-geomorphology of the basin.(2)The reservoir characteristics of Ma 56 Block in the Tiaohu Formation are clarified.The lithology of the tuff reservoir of the Ma 56 Block Tiaohu Formation is mainly powder-micro-scale tuff.The composition is mainly vitric tuff,followed by crystal-vitric tuff.The reservoir has medium-high porosity,ultra-low permeability and high.Characteristics of oil saturation.Logging response characteristics are medium-high gamma,medium-high acoustic time difference,low density,high neutron,medium-high resistance.The electrical characteristics of the Ma 56 Block tuff reservoirs are characterized by medium-high gamma,medium-high sonic time difference,low-density,high-neutron,medium-high resistance.The logging standards are as follows:RD:10~200OMM,GR:40~90API,DEN:2.10~2.50g/cm~3,CNL:20~45%,AC:240~310us/m.(3)Explain the genetic mechanism of high porosity of dense tuff in Ma 56 Block of the Tiaohu Formation.There are three main types of reservoir space in the tuffs and reservoirs of Ma 56Block and Tiaohu Formation,including primary pores,secondary pores and cracks.In the volcanic ash empty water,a relatively pure acidic tuff with low Fe and Mg and rich in Si,K and Na is formed.The organic acid formed by the organic matter rich in tuff promotes the devitrification process and the development of dissolved pores.The strong devitrification forms a large number of micropores.Although it is microporous,it is huge.Corrosion pores and cracks are also developed.At the same time,a large amount of quartz and feldspar are produced along with devitrification.Quartz increases the rigidity of the rock,and the feldspar is brittle.It plays an active role in supporting the reservoir before the fracture pressure,and preserves the pores well.In addition,the supply of land source debris is low,the clay content is low,which further plays a positive role in the development of reservoir porosity.The large number of devitrified micropores combined with the more developed dissolution pores and fractures make the tuff reservoirs of the Tiaohu Formation a high porosity feature.(4)The geological mechanism of the intensive oil injection and puff development is studied in detail in Ma 56 Block of the Tiaohu Formation.Because the tight reservoirs of the Ma 56 block have a similar mechanism of water injection and throughput in conventional reservoirs,the geological conditions of the Ma56 block tuffs are complex and the lithology is special.The geological conditions must be thoroughly understood before conducting field experiments.Therefore,based on the analysis of the characteristics of the above tuff reservoirs,a detailed and comprehensive study on the geological mechanism of water injection and puffing in tuff reservoirs is carried out.The original tuff in the tight tuff of the Permian Tiaohu Formation of the Ma56 Block is hydrophilic.The Ma 56 tuffs composition are mainly vitric tuff,followed by swarf crystal-vitric tuff.The composition is mainly felsic,and the rock is brittle.The reservoir micro porosity and fracture are development,and due to the extremely low permeability of the Ma 56 Block tuff reservoirs,the single well has an independent closed space,and the reservoir has no energy replenishment;the Ma 56 Block tuff reservoir is a high oil saturation oil.The crude oil in most areas is low in viscosity.Based on the geological mechanism suitable for water injection and puffing,the water injection and puff test was carried out in the horizontal well of Ma 56 Block.At the same time,combined with laboratory experiments and field practice,it is proved the use of water injection and puffing is an effective method to improve the tuffs tight oil recovery of Ma 56 Block.