Patent Description:
The approaches described in this section could be pursued, but are not necessarily approaches that have been previously conceived or pursued. Therefore, unless otherwise indicated herein, the approaches described in this section are not prior art to the claims in this application and are not admitted to be prior art by inclusion in this section. Furthermore, all embodiments are not necessarily intended to solve all or even any of the problems brought forward in this section.

In the past, when a subsoil composition should be determined, a same paradigm is used: "the model used for said determination should be meshed before any modeling".

Indeed, for any modeling methods, the meshing is mandatory.

Nevertheless, it is well known that this meshing prior to any modeling has several drawbacks as the size of the meshes, the orientation of the meshes, the number of the meshes induce bias in the modeling.

For instance, this meshing prior to any modeling cannot take into account the sedimentary bodies of the subsoil which will be identified during the modeling phase.

It is noted that the accurate determination of the subsoil composition and structure is a key feature for determining hydrocarbon reservoirs and enabling a proper industrial extraction of hydrocarbons.

In addition, when working with pre-meshed model, it may be difficult to accurately satisfy the well constraints (i.e. log data) as the log data may be transformed with blocking methods to adapt the precision of the log data to the dimension of the cells.

Furthermore, in prior art methods, it may be difficult to associate the cells with facies or geophysical property as the dimension of the cell does not allow a proper identification of their respective position in the geological formations.

Examples and embodiments of prior art may be found in <CIT>.

The invention relates to the methods according to claims <NUM> and <NUM>, the non-transitory computer-readable storage media according to claims <NUM> and <NUM> and the devices according to claims <NUM> and <NUM>.

In an example not covered by the invention, a method for determination of real subsoil composition comprises:.

Thanks to said method, it is possible to adequately mesh part of the model and thus to effectively run method(s) to determine real subsoil composition. The meshing is far more accurate than a priori methods of the prior art.

Therefore, a last step of the method may be to determine real subsoil composition based on the meshed formation or/and output said result for future use in geophysical tools (e.g. prevision of hydrocarbon production, determination of a correct location of a well to be drilled, estimation of the reservoir capacity).

In addition, the determination of the at least one parametric surface may be based on NURBS curve or NURBS surface or NURBS volume.

In the followings, it is possible to use any "B-splines" or "splines" instead of "NURBS".

Relating to <NPL> describes any concepts and algorithms needed to manipulate NURBS.

Optionally, the determination of the fluvial trajectory may be based on a stochastic process.

Furthermore, the meshing of the fluvial zone may be based on a method in a group comprising Quadtree meshing method, the Octree meshing method, Front method, Delaunay method, Prograding grid, divergent grid, and aggrading grid.

In addition, the method may further comprise:.

In another example not covered by the invention, a method for determination of real subsoil composition comprises:.

Thanks to said method, it is possible to create a model that easily satisfies the constraints provided. This method is far better than prior art methods as the distortion is performed on surfaces (with is very simple by known algorithms) while prior art methods deal with cells inclusion/exclusion, far more complex.

Therefore, a last step of the method may be to determine real subsoil composition based on the distorted formation or/and output said result for future use in geophysical tools (e.g. prevision of hydrocarbon production, determination of a correct location of a well to be drilled, estimation of the reservoir capacity).

The parametric surface may be based on NURBS curve or NURBS surface or NURBS volume.

In addition, the distortion of the parametric surface may comprise a prior step of determining a point in said surface minimizing a distance between a distance of said point and a position of said constraint.

The geological constraints may be based on a constraint in a group comprising a data log constraint and a seismic constraint.

Optionally, the constraint may be satisfied when a position of said constraint is inside the geological formation.

In a first aspect, the invention relates to a method for determination of real subsoil composition according to claim <NUM>.

Thanks to said method, it is possible to easily associate facies to cells.

A last step of the method is to output the model for future use in geophysical tools (e.g. prevision of hydrocarbon production, determination of a correct location of a well to be drilled, estimation of the reservoir capacity).

In a second aspect, the invention relates to a method for determination of real subsoil composition according to claim <NUM>.

Thanks to said method, it is possible to easily associate property to cells.

A last step of said method is to output the model for future use in geophysical tools (e.g. prevision of hydrocarbon production, determination of a correct location of a well to be drilled, estimation of the reservoir capacity).

Another example, not covered by the invention, relates to a computer program product comprising a computer-readable medium, having thereon a computer program comprising program instructions. The computer program is loadable into a data-processing unit and adapted to cause the data-processing unit to carry out the method(s) described above when the computer program is run by the data-processing unit.

Other features and advantages of the method and apparatus disclosed herein will become apparent from the following description of non-limiting embodiments, with reference to the appended drawings.

The present invention is illustrated by way of example, and not by way of limitations, in the figures of the accompanying drawings, in which like reference numerals refer to similar elements and in which:.

In the following description, fluvial geological formations are described to exemplify the invention but it applies to any possible geological formations (e.g. lobes, turbiditic systems, etc.).

Therefore, in the following, "fluvial trajectory" may be replaced by "sediment trajectory" without significant modification.

<FIG> is a chart describing a possible process of the invention.

In this chart, the manipulated model is possibly a parametric model of the subsoil. A parametric model Mp(u,v,t) of the subsoil is a transformation of a 3D model M(x,y,z) of the subsoil.

A 3D model M(x,y,z) of a real subsoil describes the subsoil according to its real geographical coordinates (x,y,z) (i.e. at the present time).

A parametric model Mp(u,v,t) of said subsoil describes the state of the subsoil at a geological time t: each layer represents the state of the subsoil at the time t where the sedimentation occurs. One may say that the parametric model Mp(u,v,t) restore the horizontal layer for a given sedimentation/geological time t.

In the manipulated model, it is possible to simulate the geological formation of a fluvial zone. Said geological formation determination of a fluvial zone may comprise, as described in <CIT>, the displacement of particles (step <NUM>) in the manipulated model by superimposing:.

It is possible to take into account both the fluid flow of the particles in the zone, and to introduce a probabilistic perturbation.

When one speaks of superposition of two terms, it will be understood that the simulated displacement is composed from the sum of the deterministic term and of the stochastic term.

The stochastic term can comprise the superposition of a meandriform term and of a random perturbation. So doing, the modeling of the channel is rendered more realistic.

The meandriform term can comprise a superposition of at least one trigonometric function. Such a representation is realistic for a meandriform term, and easily parametrizable.

The observation data can comprise at least one of the following types of data:.

It is noted that the model does not need to be meshed up to this point. A parametric description of the trajectory may be easily determined in the model.

Once the respective trajectory <NUM> (see <FIG>, <FIG>) of geological formation(s) of a fluvial zone is/are determined (for the sake of the understanding, the singular is used in the following, considering that only one trajectory <NUM> is determined, but it is apparent that the plural may also be used), it is possible to determine surface(s) (step <NUM>) that represent the extend of the determined geological formation, the trajectory being inside said extends. This extends may represent the bed of a river/torrent/etc. or any geological formation of the fluvial zone (see element <NUM>, <FIG>, <FIG>).

To describe these surfaces, it is possible to use NURBS (or non-uniform Rational B-Splines).

Non-uniform rational basis spline (NURBS) is a mathematical model used in computer graphics for generating and representing curves and surfaces. It offers great flexibility and precision for handling both analytic (surfaces defined by common mathematical formulae) and modeled shapes.

Therefore there is no need to identify the bed of said formations by identifying the meshes/cells of the meshed model that are inside the bed: a parametric description of said formations enables a far better meshing performed at a later stage fitting the NURBS surfaces.

For instance, in <FIG>, a side view of the model is shown, the trajectory <NUM> being perpendicular to said view. In said figure, trajectory <NUM> is represented as a single point. When refering to "point <NUM>", one means the point corresponding to the intersection between the view plan of figure and the trajectory <NUM>.

To represent the extend of the determined geological formation, it is possible to represent the shape of bed by a plurality of NURBS <NUM>, <NUM> and <NUM>, ensuring that the contacts of these NURBS satisfy some parametric continuity (for instance C<NUM>, C<NUM> and/or C<NUM>) and/or some geometric continuity (for instance G°, G<NUM> and/or G<NUM>).

In the example of <FIG>, point <NUM> and <NUM> may be defined such that <NUM>, <NUM> and <NUM> are aligned, the respective distance between <NUM>-<NUM> and <NUM>-<NUM> may be function of the local curvature of the trajectory <NUM> (see <FIG>).

In said example, point <NUM> represents a point on the convex side of the curvature of the trajectory <NUM>; point <NUM> represents a point on the concave side of the curvature of the trajectory <NUM>. Thus, it is possible to compute the distances <NUM>-<NUM> and <NUM>-<NUM> as a function of the local curvature of the trajectory <NUM> and such that the distance <NUM>-<NUM> is lower than distance <NUM>-<NUM>.

Point <NUM> may be determined such that the line (<NUM>;<NUM>) is perpendicular to the line (<NUM>;<NUM>) and such that the distance <NUM>-<NUM> is either a predetermined value or function of the local curvature or function of the distance <NUM>-<NUM>.

In addition, once the positions of points <NUM>, <NUM> and <NUM> are determined, it is possible to determine a plurality of set of points <NUM>, <NUM><NUM> and <NUM>. These points may have a location function of the positions of points <NUM>, <NUM> and <NUM> and/or the curvature of trajectory <NUM>.

Points <NUM>, <NUM>, <NUM>, <NUM> may define a first NURBS <NUM>.

Points <NUM>, <NUM>, <NUM>, <NUM> may define a second NURBS <NUM>.

A third NURBS <NUM> may be defined to close the shape of the bed.

NURBS curves may be determined thanks to the Cox-de Boor's Algorithm.

This process is described in regard of a side view of the trajectory (perpendicular to said trajectory) but can be reiterated for a plurality of different side views of the trajectory (see <FIG> for instance). Then, NURBS surfaces may be defined thanks to the NURBS curves (or thanks to points that have been used to define the NURBS curves).

The use of the NURBS surfaces is very effective as it is very simple to "substract" volumes of determined geological formations. For instance, referring to <FIG>, if two geological formations <NUM> and <NUM> are determined and if their respective volumes intersect each other, available NURBS intersection algorithms provide accurate and effective method to subtract the volume of formation <NUM> to formation <NUM> (representing the replacement of the formation <NUM> by formation <NUM> due to hydrodynamic/fluvial erosion) to create the new volume <NUM> (<FIG>). Algorithms based on cells / meshes (i.e. identifying cells that are in both formations) are not as accurate and effective as the NURBS algorithms.

In addition, if the model has some constraints (e.g. a seismic or geological indication that a formation is present at a given location), it is possible to distort the closest NURBS <NUM> to ensure that this constraint <NUM> (see <FIG>, which is a top view of the model) is satisfied. The distortion methods for NURBS surfaces are well available. Therefore it is possible to satisfy all constraints of the model.

It is also possible to distort the formation vertically to match the constraints but within a given distance / zone. For instance, if one may want to satisfy the well-data (see <FIG>) represented by layer <NUM>-<NUM>, it is possible to use directly the logs without applying a blocking method (which was mandatory in the method of the prior art, i.e. the reduction to coarser layers <NUM>-<NUM>). Thanks to said method, if it is known that a fluvial formation is in the layer <NUM> and that the closest formation is at position <NUM>, it is easy to distort the NURBS to satisfy the constraints. With a blocking method, this constraint may not be satisfied as the layer <NUM> may disappear.

Once the formations are determined thanks to the NURBS surfaces, it is possible to mesh the formations (step <NUM> of <FIG>) according to the formations surfaces definition.

A plurality of meshing is possible as described in <FIG>. For instance, meshes <NUM>, <NUM>, <NUM> or <NUM> are possible. Well known methods such as the Quadtree meshing method, the Octree meshing method, Front method, Delaunay method, Prograding grid, divergent grid, aggrading grid, etc. are possible.

It is possible to understand that the meshing performed a posteriori (i.e. after the determination of the formation shapes) is far better (i.e. fits the shape of the geological bodies) than a meshing performed a priori (i.e. before any shape determination of geological formation).

In addition, based on the first geological formations determined, it is possible to create related formations such as lobes (i.e. at an end of the fluvial formation), bar, point bar (see <FIG>, the number of internal surfaces <NUM> or the distance between surfaces <NUM> may be set by the user), or Crevasse splay or levees (fluviatil or turbiditic). Each of these associated/related formations may have their own rules regarding the meshing of these formations (for instance, in <FIG>, the size of the cells in point bar zones <NUM> or in the levee zone <NUM>.

Thanks to this method, it is possible to adequately mesh the model according to the needs and to the specific shape of the formations. If a meshing was performed prior to any formation determination, it is apparent that this meshing cannot fit the need of the modeling.

In addition the shape of other geological formations may be determined based on a distance to a previously determined formation or/and to a probability of existence of a surface of said other geological formations (function, for instance, of a distance (e.g. radial or lateral) to previously determined formations).

It is also possible to associate a facies (step <NUM> of <FIG>) to each cell of the newly created mesh (i.e. for each geological formation) as shown in <FIG>.

In this example of <FIG>, the quality index distributions are function of the distance to the vertical axis <NUM>-<NUM> of the shape of the bed and of the distance to the base <NUM> of the bed, but other geological formations may have quality index distributions function of other parameters set by the operator (i.e. the person setting the modeling).

For each cell of the geological formation that is considered, said cell having a position p, a cell quality index QIcell is computed as being <MAT> (i being the current driver, N being the total number of drivers).

Then, the following process (see <NUM>) may be used for associating a facies to a cell in a formation (having a plurality of cells):.

It is apparent that the "lowest" words may be replaced by the "biggest" in said process.

It is also possible to associate a geological property (e.g. permeability, porosity, etc.) (step <NUM> of <FIG>) to each cell of the newly created mesh (i.e. for each geological formation) as shown in <FIG>.

This association may be based on property quality index distributions QIi(p) for each driver i function of the considered (absolute or relative) position p (element <NUM> and <NUM> being respectively the property quality index distribution function of the distance to the vertical axis <NUM>-<NUM> of the shape of the bed and the property quality index distribution function of the distance to the base <NUM> of the bed) and on property distribution (curve <NUM>).

In this example of <FIG>, the property quality index distributions are function of the distance to the vertical axis <NUM>-<NUM> of the shape of the bed and of the distance to the base <NUM> of the bed but other geological formations may have property quality index distributions function of other parameters set by the operator (i.e. the person setting the modeling).

Then, the following process (see <NUM>) may be used for associating a property to a cell in a formation (having a plurality of cells):.

It is apparent that the "lowest" (respectively "biggest") words may be replaced by the "biggest" (respectively "lowest") in said process.

For part(s) of the model that is/are not determined geological formations (i.e. background zone), it is possible to mesh (step <NUM> of <FIG>) it/them with common method(s) and to associate its/their cells with property/facies (step <NUM> of <FIG>) according to the relative position of the cells in regard of the geological formation determined (e.g. facies probabilities may be set by the operator according to a radial/lateral distance of a determined geological formation).

<FIG> is a possible embodiment for a device that enables the present invention.

In this embodiment, the device <NUM> comprise a computer, this computer comprising a memory <NUM> to store program instructions loadable into a circuit and adapted to cause circuit <NUM> to carry out the steps of the present invention when the program instructions are run by the circuit <NUM>.

The memory <NUM> may also store data and useful information for carrying the steps of the present invention as described above.

This computer comprises an input interface <NUM> for the reception of data/model/input used for the above method according to the invention and an output interface <NUM> for providing a complete model.

To ease the interaction with the computer, a screen <NUM> and a keyboard <NUM> may be provided and connected to the computer circuit <NUM>.

Expressions such as "comprise", "include", "incorporate", "contain", "is" and "have" are to be construed in a non-exclusive manner when interpreting the description and its associated claims, namely construed to allow for other items or components which are not explicitly defined also to be present. Reference to the singular is also to be construed in be a reference to the plural and vice versa.

Claim 1:
A computer-implemented method for determination of subsoil composition or structure comprising:
- receiving a model representing the subsoil, said model comprising at least one parametric volume describing a geological formation in said model, said volume having a plurality of cells;
- for each cell in the plurality of cells, determining an index (QIcell) function of a respective position of the cell in the geological formation;
- receiving a set of facies, each facies in said set being associated with a proportion and an index ordering in said formation; and
- associating a facies to each cell,
characterised by
said step of associating comprising:
/a/ selecting a cell with a lowest index within cells in the plurality of cells having no facies associated to;
/b/ associating, to said cell, a facies with a lowest index ordering within facies of the set of facies for which the respective proportion is not reached in the formation;
/c/ reiterating steps /a/ to /c/ until all cells in the plurality of cells are associated with a facies; and
- outputting the model determined in step /c/ for future use in geophysical tools.