A Study On Reservoir Characteristics Of Yan 969 Well Area In Yan'an Gas Field

The Shanxi Formation reservoir in the Yan 969 well area of Yan'an Gas Field is located in the southeastern part of the Yishan Slope in the Ordos Basin.It is a typical tight sandstone gas reservoir with extremely low porosity and permeability,complex pore structure and strong reservoir heterogeneity.Seriously restricting the subsequent production and development of the gas field.Conventional single test methods are difficult to effectively evaluate the microscopic pore structure characteristics and seepage characteristics of ultra-low permeability gas reservoirs,thus restricting the exploration and development process of gas reservoirs.Based on the analysis of the petrophysical properties and pore structure of the reservoirs in the study area,this paper combines physical testing,casting thin sections,particle size analysis,high pressure mercury intrusion,nuclear magnetic resonance,infiltration experiments,and phase infiltration experiments.Based on the analysis of the basic sedimentology and petrological characteristics of the study area,the microscopic pore structure characteristics,the characteristics of the movable fluid,the characteristics of the seepage,the characteristics of gas-water phase infiltration and its influencing factors were studied..Mainly achieved the following understanding:(1)The type of sandstone in the study area is dominated by quartz sandstone(61.54%);the grain size of sandstone is dominated by fine sand(54%);the interstitial is dominated by clay,calcite and dolomite;the pore type is dissolved in rock debris,The feldspar dissolved pores,the residual intergranular pores,the intercrystalline pores and the heterogeneous dissolved pores are dominant;the throat type is mainly sheet-like and curved-shaped.(2)According to the high pressure mercury intrusion test,the pore structure of the reservoir is divided into three categories according to the discharge pressure less than 1 MPa,between 1 and 2.5 MPa,and greater than 2.5 MPa: the first type is the low discharge pressure-micro-fine throat The type of the road is type II,which is the medium-displacement drive pressure-micro-throat type,and the third type is the medium-high discharge pressure-nano-adsorption throat type,of which the type II reservoir accounts for 66.7%.The displacement pressure,the mainstream pore throat radius,the reservoir quality factor,and the mean coefficient have a great influence on the microscopic pore structure and physical properties of the reservoir.(3)The reservoirs are classified according to the fluid saturation.The study area is mainly composed of Class III(medium)(30%)and V(very poor)(30%)reservoirs.The T2 cutoff value of the sample is between 0.91 ms and 126.04 ms,with an average of 41.39 ms,which shows the characteristics of ultra-low permeability sandstone heterogeneity.Permeability is the main factor affecting the fluid saturation and T2 spectrum,and it can reflect the changing trend of the movable fluid.(4)According to the infiltration rate and the final water saturation,the reservoirs are divided into four different types.The study area mainly focuses on the I and II types of infiltration curves,accounting for 60%.Both show a high initial infiltration rate and a low water saturation.The wettability of the rock directly determines the strength of the reservoir's ability to absorb.(5)According to the morphological characteristics of the phase infiltration curve,it can be divided into three types: type I low-binding water saturation large seepage interval type;type II medium irreducible water saturation medium seepage interval type;type III high irreducible water saturation small seepage interval The curve,in which the type III curve accounts for the largest proportion,is 45%.The permeability and the average pore throat radius play a dominant role in the morphology of the phase infiltration curve.(6)Combining the rock characteristics,sedimentary characteristics,microscopic pore structure characteristics and seepage characteristics of the reservoirs in the study area,taking the size of the displacement pressure as a precondition,the reservoirs of the Shanxi Formation in Yan'an gas field Yan969 well area are divided into three types: Class I low-displacement drive pressure,Class II discharge pressure,Class III medium-high discharge pressure,respectively,showed good,moderate,poor physical properties,microscopic pore structure and seepage characteristics,and the reservoirs in the study area were mainly Class II.The reservoir is dominated,accounting for more than 50%.The research results in this paper lay a good theoretical foundation for improving the tight sandstone gas reservoirs in the Yanying gas field of Yan'an gas field,and have certain guiding significance for the development of similar gas reservoirs.