Evaluating and Mapping Gas Sand Reservoirs Using AVO Attributes and Geophysical Well Log Data in an Area of Block M9, Offshore Myanmar

Abstract

Gas sand reservoir determination is one of the challenge tasks in the petroleum industry. The study area is in the Gulf of Moattama, Mottama basin, Offshore Myanmar. It covers an area of about 275.9 square kilometers. The objective of this study is to detect gas in sandstone reservoir using amplitude versus offset attribute analysis and geophysical well log data. Amplitude crossplot of 3D seismic data set (near- and mid- angle stack) were used for AVO analysis. The geophysical well log data such as P-wave velocity, S-wave velocity, gamma ray, resistivity, density, Poisson’s ratio and acoustic impedance of four interesting reservoirs (Gas Sands A, B, C, and D) from Well 1 and Well 2 were crossplotted to determine the gas reservoirs. P-wave velocity, S-wave velocity, density and check shot data were used to create the AVO model by using Zoeppritz equation. The top of the elastic model of gas sands displayed a trough at normal incidence and the magnitude of the amplitude decreased with increasing offset. The resulting crossplot of intercept and gradient of AVO synthetic attribute of Well 1 and Well 2 showed cluster or “wet trend” about the origin and anomalous values in the second and fourth quadrants, which correspond to class IV AVO anomalies at Well 1 and Sand C and Sand D at Well 2. For the Gas Sand A of Well 2, the anomalous values fall in the first and third quadrants showing the characteristics of Class III AVO type. The RMS amplitude volume of Gas Sands A, B, C, and D with 5 ms windows showed distribution of each sand and new potential area of hydrocarbon accumulation. According to the results, AVO analysis can be used to distinguish between lithologic factors and hydrocarbons. This study can be applied for future development and locating infill wells and can also be used to evaluate the reservoir, understand more the relationship between rock and fluids.