ANALISIS ATRIBUT LAMBDA-MU-RHO (LMR) PADA RESERVOIR BATUPASIR DI DAERAH “X”(STUDI KASUS DI PT. CHEVRON INDONESIA)

Abstract

It has been done analysis of Lambda-Mu-Rho (LMR) attributes of 3D seismic data at “X” area below X horizon. The purposes of this analysis are to identify rock lithology and fluid contents of a reservoir and map the gas reservoir. LMR attributes were generated from equation which proposed by Castagna with approximation of Vp/Vs ≈2, those are μρ=Zs 2 and λρ=Zp 2-2Zs 2. P Impedance (Zp ) and S Impedance (Zs) are inverted from P wave reflectivity (Rp) and S wave reflectivity (Rs) using model based inversion method, where P wave reflectivity (Rp) is Intercept and S wave reflectivity (Rs) was generated from equation Rs=1/2(Intercept-Gradient). Intercept and Gradient are the attributes of AVO inversion. Mu-Rho (μr) or rigidity value is used to discriminate rock lithology, especially between shale and sands, Lambda-Rho (lr) or incompressibility is used to discriminate gas-sand and wet-sand because it is sensitive at fluid content of rock. Lambda-per-Mu (l/μ) is used to make clear the gas-sands mapping. The results of crossplots of well log show gas presence at target zone. The analysis of crossplot Lambda- Mu-Rho (lr, μr, and l/μ) attributes is able to predict the spreading of gas reservoir. Based on the analysis, gassands lie on zone that has Mu-Rho (μr) value higher than 7 GPA.g/cc (μr > 7 GPA.g/cc) and Lambda-Rho value lower than 21 GPA.g/cc (lr < 21 GPA.g/cc). Wet sand lie on zone that has Mu-Rho (μr) value higher than 7 GPA.g/cc (μr > 7 GPA.g/cc) and Lambda-Rho value higher than 21 GPA.g/cc (lr > 21 GPA.g/cc). Shale lies on zone that has Mu-Rho (μr) value lower than 7 GPA.g/cc (μr < 7 GPA.g/cc).