A Study On Sedimentary Characteristics In Badin Area Of Pakistan

Research indicates that there are very good conditions for oil accumulation and considerabledevelopment prospect in the overland Badin area of lower India River basin,Pakistan.But because the exploration degree of the area is generally low,intensiveand systemicstudies on depositional systems,sedimentary facies belts and the exhibition of the reservoir are lacking,which restricts the oil-gas explorationseverely.By the method of sequence stratigraphy which is mainly through core observation and analysis of drilling or logging information,this articlesets up the isochronous formation framework of the area's interval of interest,research on the types and their distribution of sedimentary facies,and make a study on the characteristics of the reservoir.Furthermore,it also clarifies the facies of every sequence,establish the sedimentary model,and predicts the types and distribution of favorablefacies,which is expected to guide the exploration.With a combination of logging,seismics and lithofaciesinformations,the sequence boundary symbols which include interface of tectonic regime transition,interface oftruncation or overlap,interface of sedimentary transition and interface of lithofaciesmutation,can be recognized.On the basis of recognization of sequence boundary and studies on cycle spatial pattern,the strata from Sembar Formation to Lower GoruFormation in the India River basin,Pakistan,can be divided into 19 third-order sequences from bottom to top,in which C1-C4 cycles belong to SembarFormation,C4-C15 cycles belong to Lower GoruFormation.Meanwhile the Lower Goru can also be divided into Lower basal sand(C5-C8),Upper basal sand(C9-C10),Lower shale—Middle sand(C11-C14)and Upper shale—Upper sand(C15-C19,from bottom to top.The distribution of strata and reservoir within the isochronous formation framework is also worked out.Through the recognization of facies indicator,analysis of single well facies and profile facies,we recognize 4 kinds of facies which include fan-delta controlled by river,coastal barrier,tide-dominated delta,continental shelf,and 20 kinds of subfacieswhich includebarrier island,tideway,subaqueous distributary channel,etc.At thesame time,the sedimentary model of 4 main facies such as fan-delta controlled by river,coastal barrier,tide-dominated delta,continental shelf are also established.Spatial distribution offacies are studied on the basis of isochronous formation frameworkdivision.River-dominated delta,which includes subfacies such as subaqueous distributary channel and mouth bar,mainly develops in Lower basal sand and distributes widly in the east of the area.barrier islandis mainly composed of barrier bar and tideway,and develops in Upper basal sand,distributes in the middle east area such as well Ghunghro-1,well Golarchi-3.Tide-dominated delta,which is generally composed of tideway and tide-modified mouth bar,develops in Middle sand and spreads in parts of Tarai block and Siran block.As for continental shelffacies,which includes neriticcarbonate shelf margin and tidal sand ridge,mainly develops in Upper sand and spreads in the middle-west area.