Data processing: measuring – calibrating – or testing – Measurement system in a specific environment – Earth science
Reexamination Certificate
2001-05-15
2004-06-22
McElheny, Jr., Donald E. (Department: 2862)
Data processing: measuring, calibrating, or testing
Measurement system in a specific environment
Earth science
C702S017000
Reexamination Certificate
active
06754588
ABSTRACT:
BACKGROUND OF INVENTION
1. Field of Invention
This invention relates generally to the field of quantitative sedimentologic and stratigraphic prediction, and more specifically, to quantitative prediction of sedimentologic and stratigraphic attributes at all locations within a basin, especially those that are remote from a set of specific data sampling locations. Sedimentologic and stratigraphic prediction is an important step in the discovery and recovery of oil, gas, and water resources.
2. Description of Relevant Art
Sedimentology is the study of rocks that are formed by: (1) the deposition of rock fragments which have been transported from their source to another location by water and/or air (e.g., sandstone and shale); (2) precipitation of minerals from a liquid or solution (e.g., salt, gypsum); and (3) remains (shells, skeletons and organic matter) of organisms (e.g., 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 and groundwater resources occur in sedimentary basins filled with strata of diverse compositions that contain fluids (water, oil, gas) in variable proportions and spatial distributions. The distribution of fluids is strongly controlled by petrophysical (e.g., porosity and permeability) and geometric (e.g., continuity and connectivity) properties of strata.
To recover 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 production 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 or gas well is drilled in a location that is most likely to achieve an economic success. In 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 or gas reservoir. In developing (producing) an oil or gas reservoir, geologic and seismic data are used to predict locations for drilling wells that will facilitate the extraction of more petroleum from the identified reservoir.
In groundwater and contaminant transport modeling, the scientific problems of correctly identifying the fluid-flow pathways are the same as they are for oil and gas exploration and production, even though groundwater typically occurs at much shallower depths. It is widely appreciated that the biggest problem in groundwater and contaminant transport modeling is the definition of subsurface stratigraphy.
Presently, several techniques are used to obtain direct or indirect information about sedimentologic and stratigraphic attributes. A common 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 other discontinuities that reflect acoustic waves 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. Seismic methods obtain indirect information (inferences) about rocks and fluids only at the sites of the seismic line. Other common techniques include coring cuttings and well logging, which involve taking samples of the various rocks and fluids encountered as a well is drilled, and inserting various instruments into the well to measure various rock and fluid properties. These techniques obtain direct and indirect information only at the coring or well sites.
Most techniques for obtaining sedimentologic and sedimentary data or inferences about their attributes are relatively expensive. Moreover, the results obtained from such techniques are limited and applicable only to the locations at which the data are taken; i.e., the data obtained by any one of these techniques at a particular location are not necessarily representative or predictive of the stratigraphy as it exists beyond a short radial distance from the precise 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. Equally important, the information is indirect, that is, the information generated are no more than geological inferences from proxy measurements. Because of these limitations, a model is needed that accurately predicts stratigraphical attributes within a given basin from a small number of data sets.
In the parent application, Ser. No. 09/239,634, filed on Jan. 29, 1999, applicant disclosed a method that solves such a problem in that it accurately predicts basin stratigraphy at locations remote from where initial geologic data sets are collected. The disclosed method utilizes data collected from a few distinct locations within a desired basin. These data are compared to a predicted set of data generated from a forward stratigraphic model that is fed a set of values for the model process parameters. The predicted and the actual data sets are compared, and if the difference is greater than a predetermined limit, the model is run again with the parameter values modified. This process is repeated until the predictions fall within the predetermined limit and are close to the measurements taken at the sample locations. In the parent application, the predicted data set produced an accurate two-dimensional depiction of the sedimentologic and stratigraphic attributes of the desired basin thus providing a significant advance over other existing modeling techniques. However, the disclosed method of the parent application lacked the capability to generate a three-dimensional model of the sedimentologic and stratigraphic attributes of the desired basin.
SUMMARY OF THE INVENTION
Accordingly, this invention is directed to using geological data generated from one or more locations to accurately predict the stratigraphy at a location or locations remote from where the geological data were initially collected to produce a three-dimensional model of the sedimentologic and stratigraphic attributes of the desired basin. In particular, geological data gathered at a specific location can be input into the disclosed process and the stratigraphy for a location as much as tens of kilometers or as close as tens of meters away from the initial data point can be accurately predicted. The ability to predict the stratigraphy is accomplished using a mathematical optimization technique known as inversion.
Quantitative stratigraphic predictions made using inversion techniques reduce risks associated with exploration and production of oil and gas, or definition of fluid-flow pathways in ground water, and enhance interpretations or predictions made from other available data sets. For instance, quantitative prediction of the stratigraphy can be used to: (1) refine what has been inferred about the stratigraphy at a remote location by other techniques; (2) explain what a particular seismic image means in terms of rock type or other stratigraphic property; (3) extend with greater confidence information recovered from a well to a volume of rock a significant distance from the well; or (4) eliminate stratigraphically unreasonable solutions from a population of possible solutions of subsurface geology predicted by other techniques.
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 realistic input parameters; (2) real stratigraphic data from a relatively small number of distinct locations within the sedimentary basin; and (3) an inversion technique that: (a) determine
Cross Timothy A.
Lessenger Margaret A.
Faegre & Benson
McElheny Jr. Donald E.
Platte River Associates, Inc.
Young James R.
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