Data processing: measuring – calibrating – or testing – Measurement system in a specific environment – Earth science
Reexamination Certificate
1999-01-29
2001-06-12
McElheny, Jr., Donald E. (Department: 2862)
Data processing: measuring, calibrating, or testing
Measurement system in a specific environment
Earth science
Reexamination Certificate
active
06246963
ABSTRACT:
FIELD OF INVENTION
The invention relates generally to the field of quantitative sedimentologic and stratigraphic prediction.
BACKGROUND OF THE INVENTION
Sedimentology is the study of sedimentary rocks that are formed by: (1) the deposition of rock fragments which have been transported from their source to another location by water or air (sandstone and shale); (2) precipitation from a liquid or solution (salt, gypsum); and (3) remains (shells, skeletons and organic matter) of organisms (limestone, coal). Sedimentary rocks are deposited in layers known as strata. Stratigraphy is the study of the origin, composition, distribution and succession of these strata.
Oil and gas reservoirs occur in sedimentary basins. To recover the petroleum from these reservoirs typically requires drilling through thousands of feet of overlying rock. The drilling of oil and gas wells is normally a very expensive endeavor. Consequently, before incurring this expense, those involved in the exploration for or exploitation of oil and gas reservoirs seek to obtain an understanding of the basin geology and, in particular, the basin sedimentology and stratigraphy so that an oil/gas well is drilled in the location that is likely to achieve the desired result. In the case of oil and gas exploration, geologic and seismic data are used to predict the location of sedimentary rocks and structures that are likely to contain an oil/gas reservoir. With respect to developing an oil/gas reservoir, geologic and seismic data are used to predict locations for drilling wells that will facilitate the extraction of more oil from the reservoir.
Presently, there are many different techniques available for obtaining sedimentologic and stratigraphic data. One technique is seismic surveying, which involves: (1) transmitting sound waves from the surface into the earth; (2) recording the waves that are reflected back to the surface when the transmitted wave encounters interfaces between strata, fractures and the like in the underlying earth; and (3) analyzing the reflected signals to make geological inferences about sedimentary rocks and fluids encountered by the waves as they propagate through the earth. Other techniques that are also used are coring and well logging, which involves taking samples of the various rocks and fluids encountered as a well is drilled, noting the extent of each particular kind of rock that is encountered during the drilling, and inserting various instruments into the well that measure various rock and fluid properties, such as porosity.
Most of the techniques for obtaining sedimentologic and sedimentary data are also relatively expensive and are limited to the locations in which the data are taken, i.e. the data obtained by one of these techniques at a particular location are not representative of the underlying geology for more than a short distance away from the location at which the data were taken. As a consequence, any conclusions drawn with respect to sedimentological and sedimentary attributes are subject to increasing uncertainty as the location of interest becomes increasingly remote from the locations at which the data are taken.
SUMMARY OF THE INVENTION
The invention is directed to the use of geological data from one or more locations to accurately predict the stratigraphy at a remote location, i.e. a location that is distantly located from the location or locations with which the geological data are associated. In one instance, geological data were used to accurately (less the 5% error) predict the stratigraphy 50 kilometers (roughly 30 miles) away from the location at which the geological data were obtained. The ability to accurately predict the stratigraphy is accomplished using a mathematical technique known as inversion. Quantitative stratigraphic predictions made with inversion reduce risks associated with exploration and production and enhance interpretations or predictions made from other data sets. For instance, quantitative prediction of the stratigraphy can be used to: (1) refine what has been inferred about the stratigraphy at the remote location; (2) explain what a particular seismic image means in terms of rock type or other stratigraphic property; or (3) extend with greater confidence information recovered from a well to the volume of rock a significant distance from the well.
In the context of sedimentology and stratigraphy, inversion involves the use of: (1) a forward model to predict stratigraphy throughout a sedimentary basin based upon the values of input parameters; (2) real stratigraphic data from a relatively small number of locations within the sedimentary basin; and (3) an inversion technique that: (a) determines the difference between the real stratigraphic data and the predictions made by the forward model for the locations at which the real stratigraphic data were obtained; and (b) if the difference is unacceptable, modifies the values of the input parameters to the forward model to achieve a closer match between the predicted stratigraphic attributes and the real or observed stratigraphic attributes. The process of using the forward model to predict the stratigraphy throughout the basin and the modification of the values of the input parameters continues until the predictions made by the forward model for the locations associated with the real stratigraphic data match or are reasonably close to the real stratigraphic data. At this point, the forward model has been tuned such that it accurately predicts the stratigraphy not just at the locations associated with the real data but also at other locations in the three dimensional volume that are remotely situated relative to the locations associated with the observed stratigraphic data.
Even though inversion had been applied in a number of geoscience and geoengineering disciplines (including seismic signal processing, well logging, potential field geophysics, petrophysics, hydrology, contaminant transport and oil maturation analysis), it has not been applied to stratigraphic analysis or to prediction of rock attributes beyond and/or between points of control. One principal reason that inversion has not been applied to stratigraphic analysis is that it was regarded as theoretically impossible. Ian Lerche, one of the world's leaders in applying inverse and other optimization techniques to geoscience and geoengineering problems, co-authored an influential paper in 1987 which concluded that the application of inversion and other optimization techniques to the analysis of sedimentary rocks was theoretically impossible (Burton et al., 1987).
The conclusion by Burton et. al. that inversion of stratigraphic data was theoretically impossible was based upon their determination that the different processes involved in producing the stratigraphy of a sedimentary basin and the different parameter values (e.g., magnitudes, rates) associated with these processes can substitute or compensate for each other to produce the stratigraphy in the sedimentary basin of interest. If different combinations of processes can produce the same stratigraphy, then it is impossible to uniquely determine the values of the input parameters of the forward model to accurately predict the stratigraphy over a three dimensional volume of earth. In mathematical terms, this condition is known as nonuniqueness.
In the development of the present invention, it was discovered that the nonuniqueness conclusion reached by Burton et. al. was attributable to two aspects of the forward model that was employed. First, the philosophies incorporated in the forward model reflected stratigraphic paradigms which we now know are not true, including: (1) the assumption that stratigraphic processes substitute for each other to produce identical products; (2) a belief that the stratigraphic record is dominantly composed of the deposits of rare, haphazard events that lack pattern and which are therefore not invertible; and (3) that conservation of mass is not a requirement of the stratigraphic process-response system. Second, the forward model used to test whether inversi
Cross Timothy A.
Lessenger Margaret A.
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