Amplitude variation with angle analysis for deepening of a well planned as an infill opportunity: A case study of a mature oil field in the Niger Delta

Abstract

A challenge in mature fields is the enhancement of field life to maximize investment. To meet this challenge, well-recovery optimization, robust geosteering for efficient well placement in terms of drainage and sweep, and the targeting of nearby undeveloped prospects or infill opportunities (IFOs) are routinely applied to prolong productivity. Quantitative interpretation schemes such as amplitude variation with angle (AVA) analysis and seismic inversion play important roles in targeting IFOs. We present the application of AVA analysis to an IFO located in a mature oil field in the Niger Delta. To mitigate a decline in oil production, an infill campaign was launched to identify IFOs in undrained areas of the field that could be combined as multilayer objectives for a well. One such IFO is the Zebra Miocene Z12 reservoir, an undeveloped reservoir that would serve as a secondary objective if a well proposed for drilling is deepened. The IFO was screened using an AVA characterization methodology that involved the integration of rock-physics analysis, comparative quality controls of the available seismic data vintages, AVA attribute analysis, and direct hydrocarbon indicator evaluation. Results from the AVA analysis indicated a high probability of finding hydrocarbons in the Z12 reservoir and thus resulted in a recommendation to extend the well into the secondary objective. The infill well was successful with results confirming hydrocarbons in the IFO, with oil production from the Z12 reservoir alone representing an increase of 17% in the field's production. The infill well has produced about 1.3 MMbbls of oil and 4.2 Bscf of gas from the Z12 IFO since startup three years ago. This has enhanced the life of the oil field, thus validating the robustness of AVA characterization in screening new IFOs.