Broadband Seismic: Ultimate Input for Quantitative Seismic Interpretation

Abstract

This article, written by Senior Technology Editor Dennis Denney, contains highlights of paper SPE 150821, ’Broadband Seismic: The Ultimate Input for Quantitative Seismic Interpretation,’ by Cyrille Reiser, Euan Anderson, and Yermek Balabekov, Petroleum Geo-Services, prepared for the 2012 SPE North Africa Technical Conference and Exhibition, Cairo, 20-22 February. The paper has not been peer reviewed. Predicting reservoir properties away from the well using seismic information is key to quantitative interpretation. Quantitative seismic interpretation combines well and seismic data with seismic interpretation or early geological information. This proposed workflow is integrated, and the quality and accuracy of individual constituents are highly important to estimate the volume of hydrocarbon in place in a particular reservoir interval accurately. If seismic data contain very strong low-frequency information and the seismic image is of high quality/resolution, it is possible to estimate the absolute impedance directly at each point within a seismic volume. Introduction The ultimate goal in finding the best places to drill exploration or production wells is to characterize the physical properties of rock formations before drilling. Ideally, it would be desirable to have quantitative information regarding key rock properties (e.g., lithology, porosity, clay content, and net-/gross-pay ratio) along with information regarding fluid types, saturations, and pore pressures of potential reservoirs. Historically, seismic images have not delivered this information because the seismic bandwidth was limited by the conventional- streamer design and acquisition method. The conventional-streamer acquisition with a single type of sensor (hydrophone) and conventional towing depth fails, in most cases, to fulfill the geoscientist requirement. Therefore, broader bandwidth is needed with as much low- and high- frequency extension as possible. There is an urgent need to characterize very complex reservoirs accurately and be able to resolve very thin remaining hydrocarbon columns. To achieve an improved seismic characterization of the reservoir and better reservoir- property prediction away from the well, high-quality broadband seismic is needed. Well data offer high vertical resolution but do not provide lateral information, whereas seismic data have densely spaced traces with limited vertical resolution. Quantitative interpretation, or seismic reservoir characterization, is a work-flow that combines well and seismic data with seismic interpretation or early geological information. This workflow is highly integrated, and the quality and accuracy of individual constituents are of great importance to develop an accurate estimate of the hydrocarbon-in-place volume in a particular reservoir interval with the main aim being to optimize the drilling location on the basis of 3D seismics. Data Acquisition New acquisition methods and technologies have been introduced to provide a broader seismic bandwidth. Advances include variable inline-streamer towing depth, acquisition with streamers at different constant depths, and dual-sensor towed streamer. The dual-sensor (combination hydrophone and vertical-velocity sensor) towed streamer enables effective removal of the sea-surface ghost by use of wavefield separation, allowing capture of the full bandwidth of the upcoming wavefield.