Quantitative Discrimination Of Carbonate Sedimentary Microfacies By Using Well Log Data

The research on sedimentary facies and microfacies is the most basic geologicalstudies in the oil field. It is also an important part of the reservoir description. Inrecent years, with the continuous improvement of the level of exploration anddevelopment of oil and gas fields, reservoir sedimentary facies analysis must becarried out for looking for favorable reservoir facies. From the sedimentarymicrofacies study one can learn the distribution and the evolution of the sand bodiesin the skeleton facies in every deposition and can predict the heterogeneity and itschanges in the internal reservoir.Sichuan Basin is an important industrial base of natural gas in China. It is one ofthe important exploration areas of marine oil and gas exploration in the South. Inwestern Sichuan, the natural gas resource potential in deep marine strata is large,especially in the Leikoupo formation. However, due to the complex heterogeneous incarbonate reservoirs in western Sichuan, the sedimentary characteristics andsedimentary curve response characteristics in this area have a certain degree ofparticularity.The study of carbonate sedimentary reservoir is based on the interpretation of thestructure and composition of the rock. And the key of the sedimentary microfaciesacquaintance is to use a variety of mathematical methods to identify the log lithofacies.Due to the log facies of the complex carbonate has multiple solutions, the lithologiclogging identification has been a difficult problem. Gray correlation analysis methodis used to identify the complex carbonate log facies in the paper. Gray correlationanalysis method is also used to the log facies interpretation of well Chuanke1inLeikoupo formation. The application results show that the gray correlation analysishas a good practical application and it is faster and much simple than the othermathematical methods and its accuracy is higher.Since different sedimentary microfacies has different depositional environment and the hydrodynamic conditions are vary from each other, the different morphologicalcharacteristics of well logs show a certain structural features in the plane distribution.Thus, using multiple log facies elements which reflected related sedimentarycharacteristic for integrated estimation, sedimentary microfacies in the formation canbe determined in theory. The previous identifying methods of sedimentary faciesfocuses on quantitative analysis in mathematical statistics or just uses a fewmathematical parameters to identify, so it is obvious that the logging features of thesedimentary environment cannot be fully reflected. All log facies factors which canreflect the sedimentary environment are used for identification and modeling in thisstudy. Multiple mathematical models are built for quantitative description based onthe seven kinds of log facies elements such as logging curve shape, amplitude, cycle,curve smoothness and so on. Then log facies pattern is established according to logfacies elements by using the preferred log facies characteristic curve.The reservoir of the Leikoupo formation in West Sichuan Depression is developedwell. The reservoir mainly is the corrosion type dolomite reservoir of mesa flat faciesin carbonate rocks whose main controlling factors are diagenesis and sedimentaryfacies. The reservoir has small amount of the weathering crust corrosion typereservoir whose main controlling factors is the ancient tectonic activity. Thesedimentary facies in Leikoupo formation is divided by the sedimentology flag.Lithology flag is the major of sedimentology flag, such as rock types and rockformations. The sedimentary subfacies in Chuanxi Leikoupo formation is evaporationplatform facies, open platform and restricted platform. While the sedimentarymicrofacies in Leikoupo formation is open subtidal microfacies, limited subtidalmicrofacies, tidal lagoon, Salted lagoon microfacies and intertidal platformmicrofacies.Combined the quantitative identification conclusions on the logging facies and itspattern resulted by gray correlation analysis with the sedimentary microfaciesdescription of well Chuanke1at Leikoupo formation, we have obtained the lithology,logging facies and sedimentary microfacies associated characteristics of wellChuanke1near the Leikoupo formation in every formation and every layer. Thus thequantitative identification of the sedimentary microfacies in this formation is carriedout.In summary, using the gray correlation analysis method to identify the lithology andquantitative numerical logging elements can be convenient to the quantitativeidentification of the sedimentary microfacies in carbonate reservoirs. The study willbe used as a guild to the oil and gas exploration in the marine carbonate reservoirs inChuanxi.