Well placement and fracture design optimization system, method and computer program product

A well design system that utilizes geological characteristics and fracture growth behavior along of a vertical stratigraphic column of the formation in order to optimize well placement and fracture stimulation designs for the entire formation.

The present application is a U.S. National Stage patent application of International Patent Application No. PCT/US2012/054266, filed on Sep. 7, 2012, the benefit of which is claimed and the disclosure of which is incorporated herein by reference in its entirety.

FIELD OF THE INVENTION

The present invention relates generally to hydrocarbon reservoir modeling and, more specifically, to a system which optimizes well placement and fracture stimulation design for wells in layered reservoirs.

BACKGROUND

At the present time, horizontal wells and hydraulic fracturing are the typical approaches utilized to exploit natural gas, condensate and oil from low quality shale reservoirs. Shale reservoirs include a wide range of rock types, with most being unproductive. Nevertheless, the industry has viewed these shale assets as resource plays and approached treatment under the assumption that they are homogeneous reservoirs. As such, “cookie cutter” well designs having uniform well and fracture spacing are traditionally adopted for well construction and fracture treatments.

Although efficient, there is at least one drawback to the conventional approach. In reality, the shale reservoirs are highly laminated and heterogeneous, having extreme variation in reservoir properties along the vertical direction. For example, due to variation in mechanical properties and stresses over the vertical strata, hydraulic fracture growth behavior will change significantly depending on the exact fracture initiation points and the properties around the initiation points. In some places, fracture height growth may be significant, while in other locations fracture height growth may be severely restricted. Therefore, the current approach of using the same treatment for each stage in each well can be very ineffective.

In view of the foregoing, there is a need in the art for a cost-effective wellbore optimization technique which considers the heterogeneous properties of the reservoir in determining well placement and fracture design.

DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

FIG. 1shows a block diagram of wellbore placement and fracture optimization (“WPFO”) system100according to an exemplary embodiment of the present invention. As will be described herein, WPFO system100provides a platform in which to determine optimal well trajectories, fracture initiation points and fracture treatment designs for a given wellbore. More specifically, exemplary embodiments of the present invention provide a design methodology which greatly increases understanding of fracture growth behavior as a function of the fracture initiation point along the vertical stratigraphic position of the reservoir. The stratigraphic position refers to the position with respect to the formation layering in the vertical plane. Since the mechanical properties, stresses and characteristics of the reservoir can vary significantly in this environment, the fracture growth behavior will change significantly dependent upon where the fracture initiation point lies within the stratigraphic column. In contrast, however, the reservoirs tend to be much more consistent in the horizontal direction, meaning that vertical slices of the formation will tend to have similar stratigraphic behavior along a horizontal well or a significant portion of a horizontal well.

Accordingly, through utilization of the present invention, optimal well placements are determined, as well as optimal fracture initiation points and fracture treatment designs along the stratigraphic layer. Such well placements could be horizontal, deviated, high angle or vertical depending upon the reservoir characteristics and the desired reservoir contact achieved through stimulation. Other benefits of the present invention include, for example, determination of well trajectories to optimize stimulation performance; optimization of fracture treatment designs (e.g., injection rates, fluid type and viscosity, proppant type or concentration, etc.) based upon the stratigraphic well location and the desired fracture properties including length, height and conductivity; avoidance of poorly producing wellbore sections due to low probability of achieving successful stimulation treatments; and identification of stratigraphic sequences requiring multiple wellbores to effectively drain due to conditions that prevent complete fracture coverage.

Referring toFIG. 1, WPFO system100includes at least one processor102, a non-transitory, computer-readable storage104, transceiver/network communication module105, optional I/O devices106, and an optional display108(e.g., user interface), all interconnected via a system bus109. Software instructions executable by the processor102for implementing software instructions stored within WPFO application110in accordance with the exemplary embodiments described herein, may be stored in storage104or some other computer-readable medium.

Although not explicitly shown inFIG. 1, it will be recognized that WPFO system100may be connected to one or more public and/or private networks via one or more appropriate network connections. It will also be recognized that the software instructions comprising WPFO application110may also be loaded into storage104from a CD-ROM or other appropriate storage media via wired or wireless methods.

In certain exemplary embodiments, WPFO application110comprises fracture simulation module112and earth modeling module114. WPFO application110utilizes fracture simulation module112to model a given fracture design. In this regard, fracture simulation module112provides full integration between actual well properties and the fracture design criteria such as, for example, pumping rates, fluid efficiencies, or treatment volumes. Accordingly, WPFO application110provides the ability to accurately model, optimize and execute fracture operations. Exemplary fracture simulation platforms include, for example, FracXpert™, StimPlan™, GOHFER™ or FracPro™. However, those ordinarily skilled in the art having the benefit of this disclosure realize a variety of other fracture simulators may also be utilized with the present invention.

Still referring to the exemplary embodiment ofFIG. 1, WPFO application110also includes earth modeling module114which provides well planning features and subsurface stratigraphic visualization including, for example, geo science interpretation, petroleum system modeling, geochemical analysis, stratigraphic gridding, facies and petrophysical property modeling. In addition, earth modeling module114models well paths, as well as cross-sectional through the facies and porosity data. Exemplary earth modeling platforms include DecisionSpace®, which is commercially available through the Assignee of the present invention, Landmark Graphics Corporation of Houston, Tex. However, those ordinarily skilled in the art having the benefit of this disclosure realize a variety of other earth modeling platforms may also be utilized with the present invention.

Moreover, WPFO application110also includes multi-domain workflow automation capabilities that may connect any variety of desired technical applications. As such, the output from one application, or module, may become the input for another, thus providing the capability to analyze how various changes impact the well placement and/or fracture design. Those ordinarily skilled in the art having the benefit of this disclosure realize there are a variety of workflow platforms which may be utilized for this purpose.

Referring toFIGS. 2A-2G, exemplary methodologies of the present invention will now be described. At step202, WPFO application110, via earth modeling module114models the desired subsurface strata116(FIG. 2B), which may be displayed on a user interface via display108. As shown, subsurface strata116comprises a plurality of formation layers118reflecting vertical heterogeneity. Some formation layers118are relatively thick, while others are very thin, each having different physical properties and stress tolerances. However, as previously mentioned, those properties of formation layers118are much more consistent in the horizontal direction.

Thus, at step204, WPFO application110extracts a representative snapshot of subsurface strata116along a vertical column that reflects a True Vertical Stratigraphic Depth (“TVSD”)120, as shown inFIG. 2C. Since formation layers118tend to be consistent over a long horizontal distance, WPFO application110essentially collapses subsurface strata116horizontally to create TVSD120. As such, TVSD120comprises data representing properties of subsurface strata116along the vertical column such as, for example, effective porosity, effective permeability, natural fracture density, pore pressure, Young's Modulus, Poisson's Ratio, brittleness coefficient, maximum horizontal stress magnitude and direction, minimum horizontal stress magnitude and direction, rock strength, total organic content, reservoir fluid saturations, etc. Thus, through analysis of TVSD120, WPFO application110applies the subsurface properties of the vertical column over the entire subsurface strata116. Accordingly, through analysis of a single vertical column of subsurface strata116, TVSD120embodies the physical characteristics of the entire length of the subsurface strata116along a horizontal or vertical wellbore.

Utilization of TSVD120is especially beneficial in that, without TVSD120, wellbore placement and fracture optimization as described herein would require modeling of vertical slices for each proposed fracture stage along a horizontal wellbore. In some cases, each stage could include up to 4 perforated intervals, and a single well could have in excess of 30 stages leading to 120 fracture designs for analysis. Such an analysis would be very cost-prohibitive. However, the present invention reduces the analysis down to a single input file, using TVSD120, and the other process features described herein for varying the initiation points so that optimized well placement and fracture designs can be established over an entire lateral length with minimal effort.

At step206, WPFO application110populates fracture simulation module112with the data embodied within TVSD120. Once fracture simulation module112has been populated with TVSD120, the fracture growth behavior of the entire length of subsurface strata116can be evaluated for any number of imitation points within the vertical stratigraphic layering sequence. The fracture growth behavior includes, for example, the specific fracture geometries (e.g., gradient, length, height, width, conductivity, etc.) for each initiation point. Accordingly, at step208, WPFO application110determines the fracture initiation points along TVSD120. The fracture initiation points may be manually selected via a user interface (not shown), using display108& I/O devices106, or may be determined by fracture simulation module112itself. For example, WPFO application110may select fracture initiation points for each formation layer118captured in earth modeling module114. In an alternative embodiment, WPFO application110may select fracture initiation points at the interface of each formation layer118, as well as in the center of each formation layer118.

Moreover, the user interface may be interactive and provide the ability to click on portions of TVSD120in a 3D space, thus selecting the desired fracture initiation points. As understood in the art, the fracture behavior will change significantly depending upon where the fracture is initiated along the formation. Those ordinarily skilled in the art having the benefit of this disclosure realize that fracture simulation module112, or similar platforms, have deterministic algorithms to select fracture initiation points, and such algorithms are envisioned within the present invention.

Nevertheless, referring toFIG. 2D, a plurality of fracture initiation points122have been selected along TVSD120. At step210, WPFO application110, again using fracture simulation module112, models the fracture growth behavior of initiation points122along TVSD120. As shown inFIG. 2D, ellipses124represent the fracture growth behavior (e.g., fracture height, length or width) of each initiation point122. However, in the alternative, a more complex representation of the fracture growth behavior as represented by fracture simulation module112may be utilized. Thus, having performed this analysis, WPFO application110now has modeled and analyzed the necessary data to “understand” the variable fracture behavior along subsurface strata116. WPFO application110can now determine the behavior of various fracture treatment plans based upon a specified well path through any portion of subsurface strata116. Accordingly, as will be further described below, certain exemplary embodiments of the present invention utilize the modeled fracture growth behavior as a geosteering tool to assist in optimal wellbore placement in order to maximize stimulation operations.

Still referring to the exemplary methodology shown inFIGS. 2A and 2E, at step212, WPFO application110then models a wellbore126utilizing the data received from TVSD120, the fracture growth behavior represented by ellipses124, and fracture initiation points122. In this exemplary embodiment, WPFO application110determines the optimal trajectory and fracture initiation points122for wellbore126. However, in an alternative embodiment, selection of the optimum well path can be manually selected or computed by WPFO application110based upon specified results. Exemplary specified results include, for example, maximum number of proposed fracture stages, desired stimulated reservoir volume and desired reservoir contact achieved with the fracture designs.

Nevertheless, in this exemplary embodiment, wellbore116is a deviated well such as, for example, a horizontal or high angle well. However, those ordinarily skilled in the art having the benefit of this disclosure realize the present invention may also be applied to vertical wells. As shown inFIG. 2E, wellbore126has been modeled along the entirety of subsurface strata116such that fracture initiation points122and fracture growth ellipses124have been mapped onto wellbore116. Although only a few fracture initiation points122and their respective fracture growth ellipses124have been mapped onto wellbore116for simplicity, note that certain exemplary embodiments may map more or less such points122and ellipses124as desired.

Still referring toFIG. 2E, it is further illustrated how modeling fracture growth behavior along TVSD120allows analysis of an infinite number of wellbores. As shown, fracture initiation points122and their respective growth ellipses124, received from analyzing TVSD120, have been mapped onto subsurface strata116along wellbore126. Since the properties of formation layers118are homogeneous in the vertical direction, WPFO application110can now predict the behavior of any number of well trajectories and fracture designs.

FIG. 2Fillustrates an alternative exemplary trajectory for wellbore126in which WPFO application110has determined (at step212) the optimal well path to cover only an upper portion of subsurface strata116.FIG. 2Gillustrates yet another exemplary path for wellbore126in which WPFO application110has determined the optimal well path to cover only a lower portion of subsurface strata116

In an alternative exemplary embodiment of the present invention, after step212, WPFO system100may also allow alteration of wellbore126. For example, the well path of wellbore126may be altered using a click and drag functionality and/or fracture initiation points122may be deleted or added. In the alternative, real-time or other well data may be received by WPFO system100affecting the analysis. As such, at step214, WPFO application110determines whether the characteristics of wellbore126have been altered. If the determination is “yes,” WPFO application110re-models the altered wellbore126as previously described. If the determination is “no,” WPFO application110will output the model at step216in a variety of forms such as, for example, a 3D interactive graphical display, chart or text report.

The exemplary embodiments and methodologies described herein may be utilized at a number of points along the wellbore design or operational processes. For example, the present invention may be utilized during the initial planning stage in order to determine where to position the wellbore and fracture initiation points. In another embodiment, however, the present invention may be utilized in real-time as the wellbore is being drilled in order to guide further operations. In yet another embodiment, the present invention may be used to determine optimal fracture initiation points along a wellbore that has been previously drilled. These and other aspects would be appreciated by those ordinarily skilled in the art having the benefit of this disclosure.

FIG. 3illustrates an alternative exemplary embodiment of the present invention whereby well placement is optimized. As stated previously, since a given fracture will not always achieve sufficient height to contact the entire subsurface strata, well placement becomes a critical component of wellbore design. Accordingly, utilizing the present invention, well placement can be optimized so that fractures more effectively contact the better quality sections of subsurface strata116.

FIG. 3illustrates subsurface strata116modeled by WPFO application110at step212. However, in this exemplary embodiment of step212, WPFO application110also determines the location of a high quality reservoir section128. As would be understood by those ordinarily skilled in the art having the benefit of this disclosure, such high quality reservoir sections may be determined by a grouping of 2 or 3 reservoir attributes in an unconventional asset. For example, combinations of the following may be utilized to identify layers that have the highest stimulation and production potential (i.e., high quality reservoir section128): Young's Modulus, Poisson's Ratio, Brittleness Index, effective porosity, effective permeability, natural fracture density, stress anisotropy, and total organic content. Moreover, although illustrated as a single section, high quality reservoir section128may comprise a plurality of formation layers118. Once the position of high quality reservoir section128has been determined, WPFO application110models wellbore126and fracture initiation points122accordingly, thereby determining the optimal well placement of wellbore126along high quality reservoir section128.

In yet another exemplary embodiment of the present invention, WPFO application110extracts representative snapshots of subsurface strata116along 2 or more vertical columns in order to determine TVSD120. In some instances, wellbore126may cross one or more faults. Therefore, WPFO application110would extract a corresponding number of vertical columns representing snapshots of subsurface strata116on each side of the fault, and then utilize this to model TVSD120. Accordingly, exemplary embodiments of the present invention are also adapted to optimize well placement and fracturing design in reservoirs that exhibit significant heterogeneity in the lateral direction.

A number of addition features may be integrated within the present invention. For example, display108may render subsurface strata116as a 3D earth model, having color coded portions reflecting formation layers118, high or low quality reservoir sections, etc. A depth scale may also be included to indicate the depth. In addition, earth modeling module114may capture all of the key parameters required to populate a reservoir simulator to predict production capability, as well as those parameters required to populate a fracture simulator module112in order to predict fracture dimensions. Exemplary key parameters include, for example, Young's Modulus, Poisson's Ratio, Brittleness Index, effective porosity, effective permeability, natural fracture density, stress anisotropy, and total organic content.

Moreover, in instances where the growth of a fracture initiation point122might extend outside a desired formation layer118or subsurface strata116, exemplary embodiments of the present invention may generate an alert indicating a danger situation such as potential contamination of a water aquifer, a gas cap that could result in production of undesirable fluids or a low pressured zone that could result in cross flow or fluid communication reducing the production potential. Accordingly, those ordinarily skilled in the art having the benefit of this disclosure realize these and other features may be integrated into the present invention.

Accordingly, significant benefits are realized through utilization of the exemplary embodiments of the present invention. As described herein, a representative stratigraphic slice, or TVSD, is used to populate a fracture simulator, which can then be used to evaluate fracture growth behavior for a multitude of initiation points within a stratigraphic sequence. Through analysis of formation geology, geophysics, petrophysics and fracture initiation placement and geometry, fracture designs are optimized. Some of the treatment parameters which may be optimized for each fracture initiation point include, for example, injection rate, fluid type and fluid viscosity, treatment volume, proppant type, proppant concentration and proppant volume.

Moreover, through analysis of the fracture behavior growth and reservoir quality, exemplary embodiments of the present invention determine if there is an optimum fracture initiation point and where that point is within the stratigraphic sequence. Thus, more effective well planning is realized which results in the maximization of stimulation performance and production. Accordingly, the present invention provides the ability to design completions in a very complex environment where effective engineering has proven be very difficult and often ignored.

The foregoing methods and systems described herein are particularly useful in planning, altering and/or drilling wellbores. As described, the system utilizes a representation of the TVSD of the subsurface strata to conduct a fracture simulation of the entire length of the strata, thus determining the optimal wellbore placement and fracture stimulation plan. Accordingly, based on the determined wellbore placement and/or fracture stimulation plan, a wellbore is planned, deviated in real-time and/or further operations are altered. Thereafter, well equipment is identified and prepared based upon the well placement or stimulation plan, and the wellbore is drilled, stimulated, altered and/or completed in accordance to the well placement or stimulation plan.

Those of ordinary skill in the art will appreciate that, while exemplary embodiments and methodologies of the present invention have been described statically as part of implementation of a well placement or stimulation plan, the methods may also be implemented dynamically. Thus, a well placement or stimulation plan may be modeled and the data utilized as a geosteering tool to update the well plan for the drilling of wellbores. After implementing the well placement or stimulation plan, the system of the invention may be utilized during the completion process on the fly or iteratively to determine optimal well trajectories, fracture initiation points and/or stimulation design as wellbore parameters change or are clarified or adjusted. In either case, the results of the dynamic calculations may be utilized to alter a previously implemented well placement or stimulation plan.

Accordingly, an exemplary methodology of the present invention provides a computer-implemented method to determine a wellbore design, the method comprising modeling subsurface strata of a geological formation, analyzing a vertical column of the subsurface strata in order to determine a true vertical stratigraphic depth (“TVSD”) of the subsurface strata, modeling fracture growth behavior for one or more fracture initiation points along the TVSD and determining the wellbore design based upon the modeled fracture growth behavior for the one or more fracture initiation points along the TVSD. In another exemplary methodology, determining the wellbore design further comprises determining the wellbore design for a horizontal or high angle wellbore. In yet another, modeling fracture growth behavior further comprises determining a position of the one or more fracture initiation points along the TVSD. In another, determining the wellbore design further comprises determining at least one of a wellbore trajectory or fracture stimulation design.

In yet another exemplary methodology, determining the wellbore design further comprises determining at least one of a location of one or more fracture initiation points along the wellbore, fracture injection rates, fracture fluid types or proppant types. In another, the methodology further comprises determining a location of a high quality reservoir section within the subsurface strata and determining optimal placement of the wellbore along the high quality reservoir section. In yet another, modeling the fracture growth behavior of the one or more fracture initiation points further comprises modeling at least one of a fracture length, fracture height, fracture weight, or proppant conductivity of the one or more fracture initiation points. In another, determining the wellbore design further comprises detecting an alteration of the wellbore design and re-modeling the wellbore design based upon the alteration. Yet another methodology further comprises generating an alert indicating a danger situation associated with the wellbore design. In yet another, the well design is utilized to drill or stimulate the wellbore.

An exemplary embodiment of the present invention provides a system comprising processing circuitry to determine a wellbore design, the processing circuitry performing the method comprising modeling subsurface strata of a geological formation, analyzing a vertical column of the subsurface strata in order to determine a true vertical stratigraphic depth (“TVSD”) of the subsurface strata, modeling fracture growth behavior for one or more fracture initiation points along the TVSD, and determining the wellbore design based upon the modeled fracture growth behavior for the one or more fracture initiation points along the TVSD. In another, determining the wellbore design further comprises determining the wellbore design for a horizontal or high angle wellbore. In yet another, modeling fracture growth behavior further comprises determining a position of the one or more fracture initiation points along the TVSD. In another, determining the wellbore design further comprises determining at least one of a wellbore trajectory or fracture stimulation design.

In yet another exemplary embodiment, determining the wellbore design further comprises determining at least one of a location of one or more fracture initiation points along the wellbore, fracture injection rates, fracture fluid types or proppant types. Another further comprises determining a location of a high quality reservoir section within the subsurface strata and determining optimal placement of the wellbore along the high quality reservoir section. In yet another, modeling the fracture growth behavior of the one or more fracture initiation points further comprises modeling at least one of a fracture length, fracture height, fracture weight, or proppant conductivity of the one or more fracture initiation points. In another, determining the wellbore design further comprises detecting an alteration of the wellbore design and re-modeling the wellbore design based upon the alteration. Yet another further comprises generating an alert indicating a danger situation associated with the wellbore design. In another, the well design is utilized to drill or stimulate the wellbore.

Yet another exemplary embodiment of the present invention provides a system to determine a well design, the system comprising a processor and a memory operably connected to the processor, the memory comprising software instructions stored thereon that, when executed by the processor, causes the processor to perform a method comprising modeling subsurface strata of a geological formation, analyzing a vertical column of the subsurface strata in order to determine a true vertical stratigraphic depth (“TVSD”) of the subsurface strata, modeling fracture growth behavior for one or more fracture initiation points along the TVSD, and determining the wellbore design based upon the modeled fracture growth behavior for the one or more fracture initiation points along the TVSD.

In addition to the foregoing, a computer program product embodying instructions to execute the steps described herein are also envisioned. Accordingly, exemplary embodiments of the present invention provide a computer program product comprising instructions to determine a well design, the instructions which, when executed by at least one processor, causes the processor to perform a method comprising modeling subsurface strata of a geological formation, analyzing a vertical column of the subsurface strata in order to determine a true vertical stratigraphic depth (“TVSD”) of the subsurface strata, modeling fracture growth behavior for one or more fracture initiation points along the TVSD, and determining the wellbore design based upon the modeled fracture growth behavior for the one or more fracture initiation points along the TVSD. In another exemplary embodiment, modeling fracture growth behavior further comprises determining a position of the one or more fracture initiation points along the TVSD. In another, determining the wellbore design further comprises determining at least one of a wellbore trajectory or fracture stimulation design. In yet another, determining the wellbore design further comprises determining at least one of a location of one or more fracture initiation points along the wellbore, fracture injection rates, fracture fluid types or proppant types.

Yet another exemplary embodiment further comprises determining a location of a high quality reservoir section within the subsurface strata and determining optimal placement of the wellbore along the high quality reservoir section. In another, modeling the fracture growth behavior of the one or more fracture initiation points further comprises modeling at least one of a fracture length, fracture height, fracture weight, or proppant conductivity of the one or more fracture initiation points. In yet another, determining the wellbore design further comprises detecting an alteration of the wellbore design and re-modeling the wellbore design based upon the alteration. In yet another, determining the wellbore design further comprises determining the wellbore design for a horizontal or high angle wellbore. In yet another, the well design is utilized to drill or stimulate the wellbore.

Although various embodiments and methodologies have been shown and described, the invention is not limited to such embodiments and methodologies and will be understood to include all modifications and variations as would be apparent to one skilled in the art. Therefore, it should be understood that the invention is not intended to be limited to the particular forms disclosed. Rather, the intention is to cover all modifications, equivalents and alternatives falling within the spirit and scope of the invention as defined by the appended claims.