Research On Remaining Oil Distribution Of Chang 4+5 Formation Of Z Well Area In A Oilfield In Northern Shaanxi

Z well area in A oilfield is located in the south-central of the northern Shaanxi slope of the Ordos Basin.The internal structure is stable and the fault is not developed.Nose-shaped uplift develops in regional area.The chang4+5 reservoir is the main production layer,the lateral distribution of the sand body is stable,and the reservoir has low porosity and low permeability.With the further study of reservoir exploration and development,there are some problems such as high water content,low production capacity and unclear potential of residual oil in some production wells in chang4+5 reservoir.Therefore,this paper studies the remaining oil distribution and the influencing factors of the chang4+5 reservoir,providing a certain theoretical basis and reference value for the development plan of chang4+5 reservoir and potential direction of remaining oil.This paper by reservoir geology,oil geology and oil and gas field development geology theory as the instruction,takes the regional geological background data,core data and logging data as the basis.Firstly,the sedimentary microfacies and reservoir heterogeneity of the chang4+5 reservoir are studied.Secondly,based on the study of sedimentary microfacies and reservoir heterogeneity,combining with the production dynamic data and well history data analysis,the remaining oil in the single well of the study area was quantitatively evaluated by single well control geological reserve calculation method,and summarized the distribution characteristics and influencing factors of remaining oil.The main results achieved and understanding are as follows:(1)The period of chang4+522 is mainly the delta front of the underwater distributary channel.The sand body thickness is lager,with wide distribution area,and well continuity.The sand body thickness is between 7.75m and 21.8m,the average thickness is 12.18m.Chang4+521and chang4+51 period of the main development of distributary bay,and the average thickness of sand bodies are 4.8m and 8.15m respectively.The results show that the main production chang4+522 reservoir with good reservoir properties,and the underwater distributary channel sand body is the most facies beltis of remaining oil.(2)The regular rhythm,homogeneous rhythm and compound positive and negative rhythm of chang4+5 reservoir is obvious,and the intercalation is developed.The chang4+522,chang4+521 reservoir heterogeneity belongs to the weak-medium,chang4+51 reservoir heterogeneity belongs to medium-strong,three layers are integrated contrast,chang4+522 reservoir heterogeneity is significantly weaker than the other two layers.(3)The remaining oil geological reserves of the single well chang4+522 reservoir is calculated quantitatively,the results show that chang4+522 reservoir oil geological reserves is 164.6×104t,the accumulated oil production is 15.07×104t,the recovery degree of geological reserves is 9.14%,the remaining oil geological reserves is 149.53×104t,and remaining recoverable reserves is 11.88×104t.Especially,z-153,z-154,z-172 well area in the west of the study area,and z-12,z-18,z-28,z-30,z-31 well area in the central,as well as z-41,z-42,z-113,z-110,z-109,z-118,z-124,z-125,z-126 well area in the east remaining oil is enriched.(4)The remaining oil distribution characteristics of the chang4+522 reservoir is mainly controlled by influence of sedimentary microfiches,reservoir heterogeneity and production development,the remaining oil is mainly enriched in underwater distributaries channel sand body with good physical properties,relatively weak heterogeneity and not perfect injection-production system.