Cyrille Reiser

Time-lapse simulator-to-seismic study - Forties field, North Sea.

Summary A Simulator-to-Seismic (S-to-S) study is conducted over the Forties field, North Sea, by combining petrophysical, engineering and geophysical data into an integrated workflow. Based on a calibrated rock physics model, static and dynamic properties from a reservoir model are converted into time-lapse synthetic seismic attributes that can be used in conjunction with conventional seismic attributes to get more insights into the interpreted 4D anomalies. The aim of the study is to better understand the drainage patterns of the reservoir and help validate the planned position of additional producer wells to ultimately reduce drilling risks.

Broadband Seismic: The Ultimate Input for Quantitative Seismic Interpretation?

Ideally, geoscientists would like to have quantitative information about rock properties, along with information about fluid content of potential reservoirs relatively directly from the seismic as this information is available as oppose to the well data. Historically, seismic images have stopped short of delivering this, as the seismic bandwidth was limited due to the conventional streamer design and acquisition method. The ability to predict reservoir properties away from the well using seismic information is a key element in quantitative interpretation. Quantitative seismic interpretation combines various types of data: well, seismic and seismic interpretation or geological prior information. Thus, this workflow is integrated and the quality and accuracy of each individual constituent is of great importance to the accurately estimate the volume of hydrocarbon in place in a particular reservoir interval. Seismic plays a key role in this, and if the seismic data contains very strong low frequency information and the seismic image is of high quality/resolution, it is possible to directly estimate the absolute impedance at each point within a seismic volume. Over the last few years, new acquisition methods and technologies exist aiming to provide a broader seismic bandwidth: streamer towed shallow at the front and going deeper at the mid of the streamer, towed acquisition with some streamers at shallow and deeper depth, and the dual-sensor towed streamer. These new broadband seismic data volumes are bringing the seismic a step closer to the reservoir and this is what we will try to demonstrate in this presentation. We will have the latest look at some of the newest and most exciting improvements in reliably unraveling the rock properties from the 3D seismic data. Introduction The ultimate goal of the oil and gas company geoscientists seeking to find the best places to drill an exploration or production well is to be able to characterize the physical properties of rock formations in the earth before the drilling. Ideally, they would like to have quantitative information regarding key rock properties such as lithology, porosity, clay content, and net-to-gross, along with information regarding fluid types, saturations and pore pressures of potential reservoirs. Historically, seismic images have stopped short of delivering this, as the seismic bandwidth was limited due to 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: broader bandwidth with as much low and high frequencies extension as possible. In this paper, we look at some of the latest and most exciting improvements in reliably unraveling the rock and fluid properties from the extended bandwidth 3D seismic. The industry is moving towards maximizing the recovery rate of the hydrocarbons already discovered. The time of easy oil is behind us. Therefore, there is an urgent need to accurately characterize very complex reservoirs, as well as being able to resolve very thin remaining hydrocarbon columns. In order to achieve an improved seismic reservoir characterization and better reservoir properties prediction away from the well, high quality broadband seismic is needed. Well data offers high

Value of the Broadband Seismic for Interpreter and Reservoir Geophysics

Ideally, geoscientists would like seismic to provide clear, objective information about the subsurface in terms of: identification of the main geological features and stratigraphic sequences, structural elements, elastic/rock properties, potential prospects and lithology-fluid content of potential reservoirs. 3D seismic has offered the greatest benefits to seismic interpreters and reservoir geoscientists in the last few decades, but historically, seismic images have stopped short of delivering on these requirements, as the seismic bandwidth was limited due to the conventional streamer design and acquisition method. Over the last few years, starting in 2007 (Tenghamn et al. 2007) with the introduction of the dualsensor towed streamer technology, new acquisition methods and technologies have been made available with the aim of providing broader seismic bandwidth without any compromise in data quality or tradeoffs in acquisition efficiency. On one side, the combination of two sensors in the streamer cable itself enables an effective removal of the sea-surface ghost by wavefield separation, allowing us to capture the full bandwidth of the upcoming wavefield. More recently, a time and depth distributed source enables the removal of the sea surface ghost on the source side (Parkes, 2011) expanding further the frequency bandwidth. Thus, interpreters and reservoir geophysicists can now have ghost free seismic enabling a significant broadening of the seismic frequency bandwidth on the low and high side of the spectra. Some results of this latest development will be presented with an end-user perspective.