Research On Logging Evaluation Method For Carbonate Reservoirs Of Dengying Formation In Gaoshiti-Moxi Area

The Gaoshiti-Moxi area located in the southeastern part of Sichuan and the structure located at the eastern end of the central Sichuan uplift.The resercoir in Sinian Dengying Formation is the main carbonate gas source in the Sichuan Basin.The pore space of the reservoir is complex and diverse,and the fractures are developed.The heterogeneity of the reservoir is very strong,which makes it difficult in logging evaluation.Based on the conventional well logging curves,the paper comprehensively uses the supporting data such as geology,mud logging,gas testing,coring,rock thinning,and core analysis data to conduct the study of routine logging evaluation methods for the Dengying Formation in the study area.The paper mainly studied five aspects:reservoir characteristics analysis,reservoir identification,modelling of reservoir parameters,identification of reservoir fluid properties,and evaluation of reservoir effectiveness.The understanding and results were obtained as following points:1)The reservoir is dominated by dolomite.Pore space is complex and diverse,and dissolved pores and fractures are developed.The three-porosity model can effectively identify connected or unconnected pore which are mainly from fractures and caves.The reservoir is divided into four types which are caved type,fracture-caved type,fracture type and dissolving hole type based on the fracture and cave identification results.But the data from the well logging curves of the caved type,fracture-caved type,fracture type reservoirs are heavily overlapped and are difficult to distinguish;2)The reservoir porosity is calculated by the three-porosity rock physics model,which has certain applicability in the study area.Based on the porosity-permeability relationship,the permeability calculation model is established in the stratified section.Because of the effect of cracks,the accuracy of the permeability model is lacking.The Archie formula with variable parameters can indicate reservoir water saturation to some extent.3)Six kinds methods are analyed to identify the layered fluid in the Dengying Formation reservoir.In addition to the absolute resistivity method,the other five fluid identification methods have certain applicability.Integrate multiple methods are better in fluid identification.4)The lower limit of reservoir physical properties is determined by two methods.The influence factors on reservoir effectiveness have been analyzed,such as sedimentary facies,structure,lithology and fractures.The results indicate that fracture-developed dolomite layers with less sand and siliceous content are the best reservoir.The paper establishes a set of routine logging evaluation methods,which is suitable for the Dengying gas reservoir in the study area.In the comprehensive evaluation of the reservoir and the preferred production interval,the paper provides a more accurate basis.