Determine the Plan Extension of Sedimentary Microfacies by Means of GR Digit Judgment

It is a hard problem to determine the plan extension of sedimentary microfacies in cases of lacking the coring wells in oil fields. This paper discussed the method of the digit judgment using. GR log data, and mapped the plan extension of the sedimentary microfacies in Wenliu area, Dongpu Depression GR has sensitive response to the petrography of clastic rock.The GR's amplitude is affected by the intermediate value of mud content, so it is available to determine the ratio of sand to mud in strata, and the composing features of GR amplitude is a symble of sedimentary rhythm on sections. The digit judgment and analysis using GR logging data involves the following steps: 1) Chose one or more core wells, analyse their sedimentary microfacies by means of petrography, sedimentary structures, grain size and so on; 2) Evaluate the judgment criterion corresponding to microfacies and establish the GR model of them; 3) Judge the types of the microfacies using GR data in no-core wells, determine and map the plan extension of sedimentary mirofacies in study area. 2) and 3) can be finished in IBM-PC XT. The plan extension of sedimentary micrlfacies of the 3+4 and 5+6 intervals in upper Sha-4 member are provided. Through the analysis of the petrography, sedimentary structure, the featuer of grainsize and the trace fossils the core of well-109, the following microfacies can be outlined: overflow, channal point bar, midfan slump turbidity, midfan shallow water turbidity and externalfan fine turbidity. The GR standard model is established and criterion values of the facies are mapped. The maps (Fig.5 and Fig.6 ) showed: 1) 3+4 intervals in upper Sha-4 member, from north to south, vary from midfan slump turbidity, midfan shallow water turbidity to externalfan fine turbidity; 2) 5+6 intervals in lower Sha-4 member are subjected to the ephemeral facies complex in which the channal . poit bar deposit distributes along the line joining well-109, well-64, well-22, and overflow deposite cover others.