Seismic Attributes Application in Horizontal Drilling of Gas-Filled Carbonate Reservoir

Abstract

Understanding the heterogeneous nature of carbonates in oil & gas remains a challenge even in mature fields. In the development stage of carbonate fields, it is critical to have effective well trajectories and placements to achieve optimum production. Seismic data, which carry key information on rock properties and hydrocarbon fluid presence, should be heavily utilized to optimize reservoir penetration to target and achieve the desired outcome. In this paper, seismic amplitudes and acoustic impedance are visualized as powerful tools to recognize porous reservoir sections in gas-filled massive carbonate build-up to direct well trajectory to reservoir sweet spots in horizontal drilling. A horizontal infill well was proposed to further develop the mature carbonate field in offshore North Madura, targeting the Kujung-I reservoir. The well was designed to have a horizontal section in the carbonate reservoir target to optimize the gas production rate. However, due to the prognosed low contrast in the thick and clean carbonate that was initially thought to be of a homogenous character, the geo-steering tool originally planned to guide the horizontal well section was not deployed. Therefore, the drilling campaign was dominantly guided by the seismic analysis adjacent to all available real-time logging data. Seismic qualitative and quantitative approaches were conducted to observe the relationship between seismic and reservoir properties in the offshore North Madura carbonate field. Qualitatively, the DSTs and log data achieved a good correlation with the seismic bright spot and were further confirmed throughout the study by the results of Simultaneous Seismic Inversion. Moreover, well sensitivity analysis indicated that the Kujung-I reservoir had a good porosity trend with respect to the Acoustic Impedance (Inverted Zp). As a result, through the application of seismic attribute analysis in conjunction with Seismic Inversion and available real-time logging data, the well successfully reached TD in the targeted zone. Due to the horizontal section having penetrated and landed in the Kujung-1 section with good reservoir properties guided by the seismic attribute, the well achieved high production flow rate.