Abstract
Fenchuganj Gas Field is located in the Surma Basin of Bangladesh and characterized by water-drive gas field. In the reservoir condition, water saturation increases as gas production rise. The fluid properties of the four individual gas zones of this reservoir at the present condition and at the gas depleted condition should be addressed with proper prediction. In this paper, we characterize the total reservoir with special emphasis on Upper Gas Zone and New Gas Zone I which are compared with other two gas zones (New Gas Zone III and New Gas Zone II) representing some modeling results (has done before by these authors) which evidences that the pore fluids have a significant effect on the acoustic impedance and the Poisson’s ratio of the reservoir rock which is directly correlated with seismic amplitudes at constant pressure with Batzle-Wang model and Gassman-Boit models. These models with varying pressure and water saturation conditions show the reasonable predicted fluid modulus against pressure for all four gas sands. The reservoir modeling from irreducible water saturation condition (90% gas saturation) to residual gas condition (10% gas saturation) provides a way to estimate values at reservoir conditions from logging conditions. Fluid bulk density increases when water saturation increases with constant pressure and stay around constant when water saturation increases with pressure drop. But overall it increases through the production path that we assumed. Amplitude versus Offset (AVO) analysis is also compared with other study models which show that seismic reflection of p-wave changes due to change of pressure and water saturation of the reservoir rock layers. This study is also showing that all four gas zones of the Fenchuganj are under gas sand category 3. We propose the modeling of fluid property in determining the convenience of time lapse seismic, predicting AVO and amplitude response, and forecasting in the study field and making production and reservoir engineering decisions.
Highlights
Reservoir characterization incorporates all the characteristics of the reservoir that are relevant to its ability to store hydrocarbons and to produce them
New Gas Zone III was found at a depth of 1656-1680m,with pressure16.3888 MPa (2377psi), temperature 46.67°C (116°F), porosity 27.3%, gas saturation 54%, water saturation 46% and salinity 8500 ppm
Using the Gassmann-Biot model at the reservoir condition, we found that the values of dry frame rigidity (G) are 6.58438 and 3.83328 GPA, bulk density (ρ) are 2.19998 and 2.1947707 g/cm3, fluid bulk modulus (Kf) are 0.068027 and 0.076594 GPA, saturated bulk modulus (KB) are 34.610512 and 16.74993 GPA, compressional wave velocity (Vp) are 4441.031 and 3118.338 m/s, shear wave velocity (Vs) are 1730.0079 and 1321.572 for Upper Gas Zone and New Gas Zone I, respectively (Table 6)
Summary
Reservoir characterization incorporates all the characteristics of the reservoir that are relevant to its ability to store hydrocarbons and to produce them. The Batzle and Wang [8] model determines fluid properties, whereas, the Gassmann-Biot model predicts the saturated rock properties in reservoir rock matrix and gives a forecast of future effects of saturated rock properties on seismic response. The AVO (amplitude variation with offset) model predicts the seismic response from the layered rock properties [11]. We aimed i) to predict the velocity, density and modulus of fluid/fluid saturated rock matrix samples for both varying saturation with constant/varying pressure using Batzle and Wang model and Gassmann-Biot model, and ii) to predict seismic response from the layered rock properties using. The formation of our targeted layers is Bokabil and Bhuban [17]
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