WISE™ Integration Studies - Integrated Studies - Technology
Well Integration with Seismic and Electromagnetics
Advances in geophysical data acquisition and interpretation have led to significant improvements in the remote imaging of earth structure and properties. However, when only a single data type is considered, ambiguities in the interpretation can remain. Integration of different geophysical data types allows the strengths of each to be exploited: this idea is at the centre of the WISE approach in which seismic, CSEM and well log data are integrated to determine the structure and properties of the earth.
Well logs provide a high resolution measurement of the properties of a reservoir and the surrounding strata, however properties can only be determined in a small area local to the well. Often measurements of reservoir properties across the extent of a field are required. Geophysical methods provide the data necessary to investigate the earth between well locations.
Seismic data are commonly used to provide images of the sub-surface, and develop high resolution geological models of structure and stratigraphy. Amplitude variation with offset (AVO) and inversion for acoustic and elastic impedance may also be used to constrain properties such as elastic moduli and density. However seismic data alone in many situations cannot give a complete picture of the reservoir.
CSEM data can be interpreted to determine the resistivity structure of the seafloor. In many situations electrical resistivity is driven by the properties and distribution of fluids in the earth. Resistivity well logs often show that commercial hydrocarbon deposits may be many times more resistive than surrounding lithologies. In principal such variations should be readily detected using CSEM tools.
However, despite the increased sensitivity of resistivity data over seismic for the determination of saturation, there are two inherent challenges to interpreting CSEM data in isolation. Firstly, the structural resolution of CSEM data is poor. Secondly, the cause of resistivity anomalies (particularly high resistivity features) cannot be uniquely linked to the presence of hydrocarbons in the subsurface when taken in isolation. In many situations these are equally likely to be caused by other high resistivity material (for example, tight carbonates, salt or volcanics).
It is clear that a careful combination of all three data types can supply information that is not available, or is unreliable from any one data type alone. By integrating complementary sources of information and exploiting the strengths of each, estimates of rock and fluid properties such as hydrocarbon saturation, lithology and porosity can be obtained with greater confidence than from any one data type alone.
The WISE approach uses a range of workflows developed for the integrated interpretation of seismic, CSEM and well log data within a consistent rock physics framework, to provide quantitative measurements of sub-surface rock and fluid properties, leading to improved reservoir characterization.
