Characteristics And Distribution Of The Lower-middle Ordovician Fault-controlled Karst Carbonatite Reservoirs Of The Shunbei Area In The Tarim Basin

Ordovician carbonatite reservoirs in Shunbei area of Tarim Basin have achieved good exploration results,but different from the typical weathered crust Karst reservoirs,the reservoirs in Shunbei area are obviously controlled by faults.Based on the analysis of thin slice,core,outcrop,logging data,seismic data and dynamic production data,this paper defined the basic characteristics of reservoir,synthesized the outcrop types and geophysical responses in order to discuss the structural characteristics of reservoir and summarized the distribution law of reservoir after analyzing the controlling effect of fault and karst on reservoir development.On the basis of thin slice,core and logging data,the study shows that the main lithology of the reservoir is mudstone,the sedimentary facies is mainly open platform facies with little high energy reef beach facies,the main reservoir space is secondary dissolution pore and structural fracture.The diagenesis is complex,mainly including comprises,compaction,dissolution,recrystallization,mud crystallization,dolomitization,dedolomitization,dissolution,cementation and filling.and there are at least two phases of dissolution and three stages of cementation and filling.Based the observation of karst outcrop in Bachu area,four kinds of karst spatial types of outcrop in field are summarized: the dissolution system near large fault,the dissolution system near small fault,the dissolution system of network crack and cave type corrosion system;After analyzing the logging data,it is found that the Ordovician strata has caves,fractures,dissolution pores and other types of reservoir space.At the same time,some types of seismic response can be identified from the 3D seismic response such as anomalous and beaded seismic reflection along with main faults,anomalous and beaded seismic reflection along with secondary fault,beaded formation reflection,the clutter outside the fault and the strong plate reflection.Based on the forward modeling experience of various kinds of seismic reflection in carbonatite rocks around the world,the relationship between outcrop,geological model and seismic reflection characteristics in the study area is discussed,and the reservoir structure of anomalous and beaded seismic reflection related to faults is analyzed.The spatial characteristics of fault-centered hole and fracture reservoir are defined.Based on drilling,seismic data and dynamic production date,the effects of fault level,sectional property and activity on the distribution of reservoir are summarized,results show that the main fault,the intersection of faults,the junction of en-echelon faults,and the reformed part of late fault are favorable parts for reservoir development.After discussing the karst background of the fresh water in the northern area of Shunbei area,results show that the karst in the middle and late stage of Caledonian has a favorable effect on the reservoir,The petrological evidence of the existence of the hydrothermal karst were also analysed.Based on the prediction of the earthquake attributes,combined with the constraint of the dynamic production date and the analysis of the control factors,It is concluded that the reservoir has a fault-control feature along the plane,and the distribution law of a certain layer-controlled feature in the vertical direction.