Patent Description:
The present inventive concept generally relates to systems and methods for obstacle detection and more particularly to the detection and avoidance of shallow karsts in subterranean formations.

Hydrocarbon production from subterranean formations generally involves the formation of one or more wellbores into an earthen surface and through at least a portion of the subterranean formation. The subterranean formation may include obstacles that impact and/or prevent drilling operations, and in many cases such obstacles are not visible in aerial surveys and the like. For example, in some reservoirs, dipping carbonate and evaporate outcrops facilitate meteoric recharge of saline aquifers, which through time create karst features. Karst features are a source of shallow drilling hazards, typically encountered within the first thousand feet (<NUM> foot = <NUM> meters) below ground level. Subterranean obstacles such as karst features, can cause loss of drilling fluid, wellbore instability, bit drops, and/or risk to surface equipment. <CIT> discloses prediction of shallow drilling hazards, such as karsts, using seismic refraction data. It is with these observations in mind, among others, that various aspects of the present disclosure were conceived and developed.

Implementations described and claimed herein address the foregoing problems by providing systems and methods for obstacle detection. According to the invention, surface mapping data from one or more satellite images of an area of interest corresponding to a subterranean formation is received. Surface topography data of the area of interest is received from one or more light detection and ranging (LiDAR) systems, and an airborne gravity data set and a seismic data set of the area of interest are received. A potential surface pad location is identified using at least one of the surface mapping data, the surface topography data, the airborne gravity data set, or the seismic data set. The potential surface pad location includes a surface hole for each of one or more wellbores. A resistivity survey is generated for the potential surface pad location. The resistivity survey includes at least one long line extending through the surface hole for each of the one or more wellbores and at least one short line extending through the surface hole of one of the one or more wellbores. Each short line intersects the long line at the surface hole of one of the one or more wellbores. It is determined whether one or more subsurface karst features are present within the subterranean formation disposed relative to at least one of the potential surface pad location or the one or more wellbores using the resistivity survey.

Further, while multiple implementations are disclosed, still other implementations of the presently disclosed technology will become apparent to those skilled in the art from the following detailed description, which shows and describes illustrative implementations of the presently disclosed technology. As will be realized, the presently disclosed technology is capable of modifications in various aspects, all without departing from the scope of the present invention, which is solely defined by the appended claims. Accordingly, the drawings and detailed description are to be regarded as illustrative in nature and not limiting.

Aspects of the presently disclosed technology generally involve systems and methods to detect obstacles, such as subsurface karst features, within a subterranean formation. According to the invention, surface mapping data is received from one or more satellite images of an area of interest, surface topography data of the area of interest is received from one or more light detection and ranging (LiDAR) systems, and an airborne gravity data set and a seismic data set of the area of interest are received. A potential surface pad location is identified in view of the surface mapping data, the surface topography data, the airborne gravity data set, and/or the seismic data set. The potential surface pad location can include a surface hole for each of one or more wellbores.

A resistivity survey is designed for the potential surface pad location. The resistivity survey may include at least one long line extending through the surface hole for each of the one or more wellbores and at least one short line extending through the surface hole of one of the one or more wellbores. Each short line intersects the long line substantially at the surface hole of one of the one or more wellbores. High resistivity areas, for example those exceeding approximately <NUM> Ohm per meter, can be identified within the resistivity survey as subsurface karst features, and the potential surface pad location and/or the one or more wellbores can be adjusted in view of the high resistivity areas to avoid the subsurface karst features or similar obstacles.

In some aspects, high resistivity areas with resistivity of approximately <NUM> Ohm per meter to approximately <NUM> Ohm per meter are identified as subsurface karst features filled with sediment and/or air, and high resistivity areas with resistivity of approximately <NUM> Ohm per meter to approximately <NUM>,<NUM> Ohm per meter are identified as subsurface karst features filled with air. A second potential pad location in view of the high resistivity areas may be identified, with a new resistivity survey for the second potential pad location being design. In one aspect, the long line includes a plurality of electrodes, and the plurality of electrodes may be disposed with substantially even spacing. The at least one short lines can include a plurality of electrodes disposed thereon at substantially even spacing. In one example, the potential surface pad location includes four linearly arranged proposed wellbores. The long line of the resistivity survey can extend through each of the four linearly arranged proposed wellbores and four short lines, and one of the four short lines extends through each of the four linearly arranged proposed wellbores. A distal electrode may be linearly disposed from the long line, thereby increasing a depth measurement for the resistivity survey. The distal electrode can be positioned approximately <NUM>,<NUM> feet (<NUM> meters) from an end of the long line. The distal electrode can create a pole dipole survey setting.

Overall, the presently disclosed technology is an integrated system and method for detect and avoid shallow drilling hazards, such as karst features, in subterranean formations during hydrocarbon production, through remote sensing, seismic, airborne gravity and resistivity surveys, and/or the like. As such, the presently disclosed technology increases production, avoids loss of drilling fluid, increases wellbore stability, decreases bit drops and risk to surface equipment, and/or the like. Other advantages will be apparent from the present disclosure.

Examples and various features and advantageous details thereof are explained more fully with reference to the exemplary, and therefore non-limiting, examples illustrated in the accompanying drawings and detailed in the following description. Descriptions of known starting materials and processes can be omitted so as not to unnecessarily obscure the disclosure in detail. It should be understood, however, that the detailed description and the specific examples are given by way of illustration only and not by way of limitation.

For example, a process, product, article, or apparatus that comprises a list of elements is not necessarily limited only those elements but can include other elements not expressly listed or inherent to such process, process, article, or apparatus.

The term "substantially," as used herein, is defined to be essentially conforming to the particular dimension, shape or other word that substantially modifies, such that the component need not be exact. For example, substantially cylindrical means that the object resembles a cylinder, but can have one or more deviations from a true cylinder.

Additionally, any examples or illustrations given herein are not to be regarded in any way as restrictions on, limits to, or express definitions of, any term or terms with which they are utilized. Instead these examples or illustrations are to be regarded as being described with respect to one particular example and as illustrative only. Those of ordinary skill in the art will appreciate that any term or terms with which these examples or illustrations are utilized encompass other examples as well as implementations and adaptations thereof which can or cannot be given therewith or elsewhere in the specification. Language designating such non-limiting examples and illustrations includes, but is not limited to: "for example," "for instance," "e.g.," "In some examples," and the like.

Although the terms first, second, etc. can be used herein to describe various elements, components, regions, layers and/or sections, these elements, components, regions, layers and/or sections should not be limited by these terms. These terms are only used to distinguish one element, component, region, layer or section from another. Thus, a first element, component, region, layer or section discussed below could be termed a second element, component, region, layer or section without departing from the teachings of the present inventive concept.

Generally, the systems and methods disclosed herein involve identifying, detecting, and avoiding one or more subsurface karst features within a subterranean formation. The identification and detection of one or more subsurface karst features within a subterranean formation can assist in pad placement and/or wellbore placement. Placing a pad and/or one or more wellbores above a subsurface karst can disrupt and/or prevent efficient operations by causing loss of drilling fluid, wellbore instability, bit drops, and/or risk to surface equipment. As such, the presently disclosed technology implements one or more of surface mapping (e.g. satellite imagery, LiDAR, etc.), air-borne gravity, three-dimensional seismic data, and resistivity data to collectively identify the location of possible sub-surface karsts within a formation. A pad drilling location may be positioned based on the location of possible subsurface karsts. By positioning the pad drilling location in this manner, a wellbore is positioned to avoid passing through subsurface karsts during drilling.

To begin a detailed description of example systems and methods for subsurface obstacle detection and avoidance, reference is made to <FIG>, which illustrates a diagrammatic cross-section view of an example earthen surface <NUM> and subterranean formation <NUM>. The earthen surface <NUM> can support shrubbery, equipment, and/or the like while having natural topographic features, including surface karsts <NUM>.

The subterranean formation <NUM> can be disposed below the earthen surface <NUM> and be formed of a plurality of layers of strata <NUM> (e.g. surface strata, subterranean formation, underlying strata, etc.). One or more subsurface karsts <NUM> can be formed with a saline aquifer within the subterranean formation <NUM>, thus posing drilling risks involved with formation of one or more wellbores through these locations.

The surface karsts <NUM> and/or the subsurface karsts <NUM> can be formed through the meteoric recharge of saline aquifers within the subterranean formation. The subsurface karsts <NUM> can be filled with air, sediment, water, and/or combinations thereof. Identification and detection of the subsurface karsts <NUM> through the presently disclosed technology prevents wellbore washout, drilling fluid loss, abandonment of surface wellbore locations, and/or the like. Thus, the presently disclosed technology identifies the possible locations of the subsurface karsts <NUM> using surface mapping (e.g. satellite imagery, LiDAR, etc.), air-borne gravity, three-dimensional seismic data, and/or resistivity data.

Turning to <FIG>, in one implementation, a drilling pad <NUM> is positioned on the earthen surface <NUM> based on the possible locations of the subsurface karsts <NUM>. The drilling pad <NUM> may be positioned on the earthen surface <NUM> to form a plurality of wellbores <NUM> through the earthen surface <NUM> and into the subterranean formation <NUM>.

The subsurface karsts <NUM> can vary over relatively short distances (e.g. <NUM> feet (<NUM> meters)), such that when the plurality of wellbores <NUM> are planned in straight lines spaced between approximately <NUM> feet and <NUM> feet (<NUM> meters and <NUM> meters), the plurality of wellbores <NUM> can often encounter varying substrates including competent substrate and karst breccia. As can be appreciated in <FIG>, in one example, the plurality of proposed wellbores <NUM> includes proposed wellbores <NUM> and <NUM>, which can be formed through the subterranean formation <NUM> without intersecting with any of the subsurface karsts <NUM>. However, proposed wellbores <NUM> and <NUM> of the plurality of wellbores <NUM> would pass through at least a portion of the subsurface karsts <NUM>, which may adversely affect drilling operations, such that the drilling pad <NUM> may need to be relocated to another location. Such relocations may be costly in terms of time and resources during hydrocarbon production.

As such, the identification and detection of the subsurface karsts <NUM> is generated through surface mapping, air-borne gravity, three dimensional seismic data, and resistivity logs to assist in locating the drilling pad <NUM> to prevent the plurality of proposed wellbores <NUM> from encountering one or more of the subsurface karsts <NUM>.

As can be understood from <FIG>, in one implementation, the detection of subsurface karst features utilizes surfacing mapping including high resolution satellite, aerial, and/or drone imagery. For example, <FIG> illustrates a satellite image of an earthen surface of interest in full frame and natural colors format, while <FIG> illustrates a satellite image of the earthen surface of interest in a full frame IR format. Additionally, <FIG> illustrates a satellite image having a higher spatial resolution than <FIG>. <FIG> has been image processed with a Principle Component Analysis to examine a proposed drilling location and enhance the surface karst features. In at least one example, <FIG> can be supplemented with aerial drone imagery to view proposed wellsite/pad infrastructure. A surface mapping of the proposed wellsite as provided by <FIG> can additionally include a high-resolution surface topography.

Referring to <FIG>, diagrammatic views of an example LiDAR system <NUM> is shown. The LiDAR system <NUM> can be implemented to generate very high resolution images of the proposed area of interest for drill pad/well site location.

In one implementation, the LiDAR system <NUM> can determine topography through the emission of a pulsed laser <NUM> and determination of emissions returns. As shown in <FIG>, where a passive sensor <NUM> is utilized to capture light, in some cases, vegetation and similar obstructions <NUM> prevent or otherwise limit the amount of data captured to the earth surface <NUM>. However, an active sensor <NUM> may be utilized to emit the pulsed laser <NUM>, such that it penetrates to the earth surface <NUM>. As can be understood from <FIG>, where the earth surface <NUM> is bare or contains a uniform obstacle <NUM>, only a single return is expected, while in the event of non-uniform obstacles <NUM>, such as vegetation, multiple returns can be received (e.g., caused by the top of the vegetation, intermediate vegetation, and bottom vegetation). As shown in <FIG>, in one implementation, a GNSS reference station <NUM>, a GNSS receiver <NUM>, and an inertial measurement unit <NUM> may be used to control, navigate, and otherwise operate the LiDAR system <NUM> to capture topography of a location using a laser scanner <NUM>.

<FIG> illustrates an aerial image of an example area of interest, while <FIG> illustrates a shaded LiDAR topography of the area of interest. <FIG> illustrates a 3D rendition of the point-cloud generated using LiDAR. The aerial imagery of <FIG> along with the LiDAR imagery of <FIG> can assist in the identification of surface karst features within the area of interest.

<FIG> illustrates example flight lines of an air-borne gravity data, while <FIG> illustrates a hill shaded image of example air-borne gravity data. In one implementation, the airborne gravity data <NUM> is acquired via a plurality of flight lines <NUM> flown at a predetermined altitude. The airborne gravity data <NUM> can be implemented with Curvature analysis of the ZZ tensors field data, thus providing qualitative analysis of subsurface karst features, as shown for example in <FIG>.

Turning to <FIG>, a three-dimensional (3D) seismic data set of an example area of interest is illustrated. Land seismic data may be obtained for an area of interest; however, due to acquisition settings, the seismic reflection data is too deep for karst detection. More particularly, most land seismic data observes compressional seismic data at around <NUM>,<NUM> feet (<NUM> meters), while subsurface karsts are generally present less than <NUM>,<NUM> feet (<NUM> meters) in depth. The land seismic reflection data is thus not applicable in shallow karst detection. However, velocity profiles predicted from ground roll noise along show lines and receiver lines can be utilized for karst detection as described herein. A subsurface karst feature filled with air, for example, has a very low velocity compared to very high background carbonate velocity in a subterranean formation.

During land seismic data acquisition, ground roll data may be recorded together with reflection data. The ground roll data is generally treated as noise and thus disregarded during seismic processing. The ground roll data can be processed and inverted for shear wave velocity to assist in identifying and detecting subsurface karst features. The spacing between shot lines and receiver lines in acquired seismic data is normally too large for well placement determination if the seismic line is not located close enough to the proposed wellsite and/or wellbore locations.

Accordingly, as can be appreciated in <FIG>, in one implementation, a seismic data log <NUM> is provided along one of the seismic shot lines. A proposed well <NUM> is projected over the seismic data log <NUM>. The seismic data log <NUM> illustrates an inverted ground roll data for shear wave velocity, which is generally low in the unconsolidated/reworked rock layer between <NUM> and <NUM> feet (<NUM> and <NUM> meters) of depth. Within a few hundred feet (<NUM> foot = <NUM> meters) from the proposed well <NUM>, there is a velocity anomaly <NUM> where low velocity (~<NUM> ft/s, ~ <NUM>/s) is surrounded by higher velocity (~<NUM> ft/s, - <NUM>/s). The velocity anomaly <NUM> is identified as a subsurface air-filled karst feature, and flagged as a potential drilling hazard for further evaluation by resistivity data, discussed below with respect to <FIG>, <FIG>, and <FIG>.

<FIG> illustrates a diagrammatic view of an example resistivity survey design <NUM>. While airborne gravity data, such as that illustrated in <FIG>, provides a regional view of a possible subsurface karst feature and cavern anomalies, the spatial resolution may be insufficient to determine a drilling location without risk of subsurface karst interaction. As such, the resistivity survey design <NUM> is generated accordingly.

In one implementation, the resistivity survey design <NUM> includes a quad pad determining proposed well locations <NUM> (e.g. four surface hole locations) positioned at a desired drilling location. The resolvable depth for subsurface anomalies is directly related to a length of line. Longer lines can achieve deeper penetration into the ground but at less vertical resolution. Thus, to obtain optimized inverted results, resistivity lines of the resistivity survey design <NUM> include a consistent azimuth and spacing between electrodes.

In one example, a long line <NUM> can have a plurality of electrodes (e.g., <NUM> electrodes) centered based on the proposed well locations <NUM>. The electrodes can be spaced approximately <NUM> feet (~<NUM>) apart, for example. To achieve a deeper depth of penetration, an additional electrode may be added at the end of the long line <NUM>. This electrode may be placed approximately <NUM>,<NUM> feet Z (<NUM> meters) from the line end. The pole-dipole setting generates a deeper depth of investigation, while maintaining currency throughout the entire electrode string. Short lines <NUM> may have a second plurality of electrodes (e.g., <NUM> electrodes) disposed thereon. The short lines <NUM> can be centered at proposed well locations and have electrodes spaced approximately <NUM> feet (~<NUM>) apart. The spacing between adjacent short lines <NUM> can be equal to or less than the spacing between proposed surface hole locations. In one examples, a spacing <NUM> may be approximately <NUM> feet (<NUM>), depths <NUM> and <NUM> may each be approximately <NUM> feet (~<NUM>), and lengths <NUM> and <NUM> may be approximately <NUM> feet (~<NUM>). However, other proportions are contemplated.

In some instances, high resolution aerial imagery (for example, satellite imagery obtained in <FIG>) can be implemented to assist in the layout of the resistivity lines. Impact of possible existing obstacles are further taken into account, including, but not limited to, existing drilling pads (and material thereof), roads, rock piles, facilities (e.g. metal pipes), mud and/or water pits, and the like. Surveying equipment may be utilized to establish line and positioning of each probable location, and end points of each resistivity line may be determined using GPS equipment, for example.

Turning to <FIG>, an example one dimensional resistivity profile for a wellsite is illustrated, with the resistivity profile detailing <NUM> degrees west of proposed well locations. <FIG> illustrates another example one dimensional resistivity profile for a wellsite, with the resistivity profile detailing <NUM> degrees east of proposed well locations. The resistivity profiles illustrate data collected according to a resistivity survey, such as the resistivity survey design <NUM>. In the example of <FIG>, the resistivity survey design <NUM> generating the resitivity profiles may include a long line that positions <NUM> electrodes with approximately <NUM> feet (<NUM> foot = <NUM>) of spacing between them and spacing between adjacent short lines set at approximately feet (<NUM> foot = <NUM>).

As in the illustrated in <FIG> and <FIG>, a well location is placed and encounters a subsurface karst <NUM>. The subsurface karst <NUM> can cause drilling fluid loss, thus requiring abandonment and plugging of the well. The subsurface karst <NUM> is detailed by the high resistivity feature being filled partially or completely with air. However, as can be appreciated in <FIG> and <FIG>, other well locations are positioned and arranged to prevent encounter with any high resistivity features, such as subsurface karst features. While the well location is shown in <FIG> as encountering a high resistivity feature at approximately <NUM> feet (<NUM> foot = <NUM>) in depth, this feature is not present on <FIG>, meaning that the feature is likely not to intersect the actual well location due to size of the potential karst feature and direction of the well location.

In one example, where the resistivity is <NUM> Ohm-meters or less, it may indicate a karst filled with brine water or casing effect, while a resistivity of between <NUM>-<NUM> Ohm-meters indicates background subterranean formation with no karst present. A resistivity of between <NUM>-<NUM> Ohm-meters may indicate a transitional area that is less likely to have karst. On the other hand, a resistivity of between <NUM>-<NUM> Ohm-meters indicates karst filled with sediment and partially air, and a resistivity of <NUM>-<NUM>,<NUM> Ohm-meters indicates a karst filled with air.

<FIG> and <FIG> detail how a relatively small difference in surface hole location and wellsite positioning may impact whether subsurface karst features are encountered. Significant relocation of a proposed wellsite may not be needed in response; however, strategic positioning of the well locations can prevent encountering subsurface karsts, thus requiring abandonment of one or more wellbores and determining new proposed wellsite locations.

Turning to <FIG>, an example resistivity profile <NUM> through a proposed wellsite with one or more planned wellbores is shown. The resistivity profile <NUM> can be generated by a resistivity survey design, such as detailed with respect to <FIG>, with a single long line and four short lines arranged over a proposed pad location <NUM> for one or more wellbores <NUM>.

In one implementation, a long resistivity line can be placed in an East-West direction, such that the long line passes through each of the surface locations of the one or more wellbores <NUM>. Short resistivity lines can be placed in a North-South direction, while intersecting the long resistivity line at the surface locations of the one or more wellbores <NUM>. The spacing between adjacent wellbores of the one or more wellbores <NUM> can be approximately <NUM> feet (<NUM> foot <NUM>), for example.

In at least one instance, a distal electrode can be added approximately <NUM>,<NUM> feet (<NUM> foot <NUM>) from the end of the long resistivity line. While the <FIG> illustrates a distal electrode at approximately <NUM>,<NUM> feet (<NUM> foot <NUM>), it is within the scope of this disclosure to place a distal electrode at any distance away from the end of the long resistivity line including, but not limited to, <NUM> feet, <NUM>,<NUM> feet, <NUM>,<NUM> feet (<NUM> foot <NUM>), any distance therebetween, or any other distance operable to improve the resistivity profile. The pole dipole setting can increase the depth of penetration to approximately <NUM>-<NUM> feet (<NUM> foot = <NUM>), which provides sufficient coverage for exploring karst features in a subterranean formation area.

As can be appreciated in <FIG>, the resistivity profile <NUM> details a single subsurface karst feature <NUM> on the Eastern end of the line and away from the proposed one or more wellbores <NUM>. The subsurface karst feature <NUM> has a resistivity reading exceeding <NUM>,<NUM> Ohm per meter, which indicates a likely air-filled karst feature. Thus, the proposed pad location <NUM> is appropriate as the one or more wellbores placed therein are unlikely to encounter drilling disruptions caused by subsurface karst features <NUM>.

<FIG> illustrates example operations <NUM> that may be implemented with respect to the systems and devices, as described with respect to <FIG>. While the method <NUM> is shown and described with respect to operations <NUM>-<NUM>, it is within the scope of this disclosure to implement additional operations not specifically described with respect to the operations <NUM>. Further, while operations are described sequentially, no specific order is implied nor required.

In one implementation, an operation <NUM> acquires surfacing mapping, surface karsting, and/or subsurface karsting data sets. The system can receive surface mapping using aerial images, and surface karsting data from satellite data and related imagery. The system can also receive subsurface karsting data from airborne gravity and seismic data.

An operation <NUM> identifies a potential surface drilling pad location within the area of interest. The potential surface pad location can be placed based at least in part on the surface mapping, aerial surface karsting, and/or airborne gravity subsurface karsting. An operation <NUM> defines a resistivity design for the area of interest. The resistivity design can be based at least in part on the surface mapping, aerial surface karsting, and/or airborne gravity subsurface karsting. In one implementation, the resistivity design can be determined in view of the potential surface pad location for one or more wellbores.

According to the invention, an operation <NUM> generates a resistivity survey for the area, and an operation <NUM> generates a karst assessment for the area of interest to detect and identify potential subsurface karsts present adjacent to the potential surface pad location and/or one or more potential wellbores formed at the potential surface pad location. An operation <NUM> determines whether one or more subsurface karst features are present. The one or more subsurface karst features can identified and detected to determine their location within the area of interest including whether one or more of the proposed wellbores formed from the potential surface pad location would intersect any of the one or more subsurface karst features. Additionally, the size, shape, and overall resistivity of the subsurface karst feature can further determine the placement of one or more of the wellbore locations.

If the operation <NUM> identifies any karst features, an operation <NUM> moves the proposed surface pad location. The system can determine the one or more subsurface karst features will be intersected by one or more of the proposed wellbore, thus leading to drilling operation issues. Moving the surface pad location, even small distances any one or more directions can be achieved to prevent wellbores from intersecting one or more subsurface karst features. The operation <NUM> may be repeated to generate a new resistivity survey at the newly selected surface pad location.

If the operation <NUM> identifies any karst features, an operation <NUM> leaves the proposed surface pad location despite of the presence of one or more subsurface karst features. The proposed surface pad location and the one or more proposed wellbores therewith may be arranged so that they do not intersect or interact with the identified and detected one or more subsurface karst features. In this instance, movement of the proposed surface pad location in one or more directions may increase the likelihood of intersecting one or more subsurface karsts.

Where the operation <NUM> determines that no potential karst features are present, an operation <NUM> stakes the proposed surface pad location. The proposed surface pad location can be staked and prepared for the formation of one or more wellbores therein.

In various examples, different types of karst may be identified while drilling using the presently disclosed technology, with some wellsites being relocated based on the identifications to avoid an encounter with the karst. In a series of specific examples, air-filled karst were detected during drilling with two wells being relocated in one example, air-filled karst were detected during drilling with four wells being relocated in another example, partial air-filled and air-filled karst were identified and with <NUM> wells being relocated in another example, partial air-filled and air-filled karst were identified and with <NUM> wells being relocated in another example, and sediment filled, air-filled, partial air-filled, and/or other karst types were identified in other examples where the wells were not drilled, the proposed wells were safe distances from the karst features, or the wells were drilled with caution. In this series of examples, a total of <NUM> wells were relocated and <NUM> operation days were saved.

Turning to <FIG>, example resistivity profiles for an example wellsite are illustrated. The resistivity profiles depicted in <FIG> show 3D resistivity profiles, while <FIG> illustrate 2D resistivity profiles for the example wellsite. <FIG> depicts an apparent resistivity crossplot; <FIG> shows an inverted resistivity image; <FIG> illustrates a 3D resistivity contour plot; <FIG> shows another 3D resistivity contour plot, focused on zones that are less than <NUM> ohm-meters; <FIG> shows another 3D resistivity contour plot, focused on zones that are greater than <NUM> ohm-meters; <FIG> shows another 3D resistivity contour plot, focused on zones that are between <NUM>-<NUM> ohm-meters; and <FIG> shows another view of the 3D resistivity contour plot, focused on the zones that are between <NUM>-<NUM> ohm-meters. Meanwhile, <FIG> illustrate 2D resistivity profiles for long line <NUM> and long line <NUM>, respectively, of the wellsite, and <FIG> illustrate 2D resistivity profiles for short lines <NUM>-<NUM>, respectively, of the wellsite.

<FIG> illustrate an example survey and analysis of subterranean features for another example wellsite. In this example, airborne gravity data, satellite data, topography and seismic data are utilized to select a drilling pad location and <NUM> surface hole locations (SHL). A resistivity survey is utilized to further evaluate subsurface karst at the proposal SHLs. Referring to <FIG>, airborne gravity data indicates that there is no air-born gravity anomaly present at the proposed drilling pad location <NUM>, no surface karst is detected from satellite data at the proposed drilling pad location <NUM>, and the proposed drilling pad location <NUM> has a clean surface condition based on LiDAR and areal imagery data. Turning to <FIG>, a ground resistivity survey design is depicted. In one implementation, line centers are defined by wellhead locations, with two long lines passing through wellheads and each line having <NUM> probes with <NUM> feet (<NUM> foot <NUM>) of spacing between the probes. Further, four short lines are oriented perpendicularly to the long lines at the well locations, with each short line having <NUM> probes and <NUM> feet (<NUM> foot <NUM>) of spacing between the probes. As shown in <FIG>, the resistivity data shows that the long line <NUM> indicates no karst present at locations <NUM>-<NUM>, while the short lines <NUM> and <NUM> indicate air-filled karsts and the locations <NUM> and <NUM> and the short lines <NUM> and <NUM> indicate air-filled karsts at locations <NUM> and <NUM>. <FIG> shows an updated resistivity survey following movement of locations <NUM>-<NUM> to new locations corresponding to long line <NUM>. <FIG> shows resistivity data where long line <NUM> indicates no karst at the new locations. Thus, in this example, four wells were moved and the wells were drilled without incident, successfully avoiding karsts.

Referring to <FIG>, a detailed description of an example computing system <NUM> having one or more computing units that may implement various systems and methods discussed herein is provided. It will be appreciated that specific implementations of these devices may be of differing possible specific computing architectures not all of which are specifically discussed herein but will be understood by those of ordinary skill in the art.

The computer system <NUM> may be a computing system is capable of executing a computer program product to execute a computer process. Data and program files may be input to the computer system <NUM>, which reads the files and executes the programs therein. Some of the elements of the computer system <NUM> are shown in <FIG>, including one or more hardware processors <NUM>, one or more data storage devices <NUM>, one or more memory devices <NUM>, and/or one or more ports <NUM>-<NUM>. Additionally, other elements that will be recognized by those skilled in the art may be included in the computing system <NUM> but are not explicitly depicted in <FIG> or discussed further herein. Various elements of the computer system <NUM> may communicate with one another by way of one or more communication buses, point-to-point communication paths, or other communication means not explicitly depicted in <FIG>.

The processor <NUM> may include, for example, a central processing unit (CPU), a microprocessor, a microcontroller, a digital signal processor (DSP), and/or one or more internal levels of cache. There may be one or more processors <NUM>, such that the processor <NUM> comprises a single central-processing unit, or a plurality of processing units capable of executing instructions and performing operations in parallel with each other, commonly referred to as a parallel processing environment.

The computer system <NUM> may be a conventional computer, a distributed computer, or any other type of computer, such as one or more external computers made available via a cloud computing architecture. The presently described technology is optionally implemented in software stored on the data stored device(s) <NUM>, stored on the memory device(s) <NUM>, and/or communicated via one or more of the ports <NUM>-<NUM>, thereby transforming the computer system <NUM> in <FIG> to a special purpose machine for implementing the operations described herein. Examples of the computer system <NUM> include personal computers, terminals, workstations, mobile phones, tablets, laptops, personal computers, multimedia consoles, gaming consoles, set top boxes, and the like.

The one or more data storage devices <NUM> may include any non-volatile data storage device capable of storing data generated or employed within the computing system <NUM>, such as computer executable instructions for performing a computer process, which may include instructions of both application programs and an operating system (OS) that manages the various components of the computing system <NUM>. The data storage devices <NUM> may include, without limitation, magnetic disk drives, optical disk drives, solid state drives (SSDs), flash drives, and the like. The data storage devices <NUM> may include removable data storage media, non-removable data storage media, and/or external storage devices made available via a wired or wireless network architecture with such computer program products, including one or more database management products, web server products, application server products, and/or other additional software components. Examples of removable data storage media include Compact Disc Read-Only Memory (CD-ROM), Digital Versatile Disc Read-Only Memory (DVD-ROM), magneto-optical disks, flash drives, and the like. Examples of non-removable data storage media include internal magnetic hard disks, SSDs, and the like. The one or more memory devices <NUM> may include volatile memory (e.g., dynamic random access memory (DRAM), static random access memory (SRAM), etc.) and/or non-volatile memory (e.g., read-only memory (ROM), flash memory, etc.).

Computer program products containing mechanisms to effectuate the systems and methods in accordance with the presently described technology may reside in the data storage devices <NUM> and/or the memory devices <NUM>, which may be referred to as machine-readable media. It will be appreciated that machine-readable media may include any tangible non-transitory medium that is capable of storing or encoding instructions to perform any one or more of the operations of the present disclosure for execution by a machine or that is capable of storing or encoding data structures and/or modules utilized by or associated with such instructions. Machine-readable media may include a single medium or multiple media (e.g., a centralized or distributed database, and/or associated caches and servers) that store the one or more executable instructions or data structures.

In some implementations, the computer system <NUM> includes one or more ports, such as an input/output (I/O) port <NUM> and a communication port <NUM>, for communicating with other computing, network, or vehicle devices. It will be appreciated that the ports <NUM>-<NUM> may be combined or separate and that more or fewer ports may be included in the computer system <NUM>.

The I/O port <NUM> may be connected to an I/O device, or other device, by which information is input to or output from the computing system <NUM>. Such I/O devices may include, without limitation, one or more input devices, output devices, and/or environment transducer devices.

In one implementation, the input devices convert a human-generated signal, such as, human voice, physical movement, physical touch or pressure, and/or the like, into electrical signals as input data into the computing system <NUM> via the I/O port <NUM>. Similarly, the output devices may convert electrical signals received from computing system <NUM> via the I/O port <NUM> into signals that may be sensed as output by a human, such as sound, light, and/or touch. The input device may be an alphanumeric input device, including alphanumeric and other keys for communicating information and/or command selections to the processor <NUM> via the I/O port <NUM>. The input device may be another type of user input device including, but not limited to: direction and selection control devices, such as a mouse, a trackball, cursor direction keys, a joystick, and/or a wheel; one or more sensors, such as a camera, a microphone, a positional sensor, an orientation sensor, a gravitational sensor, an inertial sensor, and/or an accelerometer; and/or a touch-sensitive display screen ("touchscreen"). The output devices may include, without limitation, a display, a touchscreen, a speaker, a tactile and/or haptic output device, and/or the like. In some implementations, the input device and the output device may be the same device, for example, in the case of a touchscreen.

The environment transducer devices convert one form of energy or signal into another for input into or output from the computing system <NUM> via the I/O port <NUM>. For example, an electrical signal generated within the computing system <NUM> may be converted to another type of signal, and/or vice-versa. In one implementation, the environment transducer devices sense characteristics or aspects of an environment local to or remote from the computing device <NUM>, such as, light, sound, temperature, pressure, magnetic field, electric field, chemical properties, physical movement, orientation, acceleration, gravity, and/or the like. Further, the environment transducer devices may generate signals to impose some effect on the environment either local to or remote from the example computing device <NUM>, such as, physical movement of some object (e.g., a mechanical actuator), heating or cooling of a substance, adding a chemical substance, and/or the like.

In one implementation, a communication port <NUM> is connected to a network by way of which the computer system <NUM> may receive network data useful in executing the methods and systems set out herein as well as transmitting information and network configuration changes determined thereby. Stated differently, the communication port <NUM> connects the computer system <NUM> to one or more communication interface devices configured to transmit and/or receive information between the computing system <NUM> and other devices by way of one or more wired or wireless communication networks or connections. Examples of such networks or connections include, without limitation, Universal Serial Bus (USB), Ethernet, Wi-Fi, Bluetooth®, Near Field Communication (NFC), Long-Term Evolution (LTE), and so on. One or more such communication interface devices may be utilized via the communication port <NUM> to communicate one or more other machines, either directly over a point-to-point communication path, over a wide area network (WAN) (e.g., the Internet), over a local area network (LAN), over a cellular (e.g., third generation (<NUM>) or fourth generation (<NUM>)) network, or over another communication means. Further, the communication port <NUM> may communicate with an antenna or other link for electromagnetic signal transmission and/or reception.

In an example implementation, surface mapping, air-borne gravity, three dimensional seismic data, and/or resistivity logs, and software and other modules and services may be embodied by instructions stored on the data storage devices <NUM> and/or the memory devices <NUM> and executed by the processor <NUM>.

The system set forth in <FIG> is but one possible example of a computer system that may employ or be configured in accordance with aspects of the present disclosure. It will be appreciated that other non-transitory tangible computer-readable storage media storing computer-executable instructions for implementing the presently disclosed technology on a computing system may be utilized.

In the present disclosure, the methods disclosed may be implemented as sets of instructions or software readable by a device. Further, it is understood that the specific order or hierarchy of steps in the methods disclosed are instances of example approaches. Based upon design preferences, it is understood that the specific order or hierarchy of steps in the method can be rearranged while remaining within the disclosed subject matter.

The described disclosure may be provided as a computer program product, or software, that may include a non-transitory machine-readable medium having stored thereon instructions, which may be used to program a computer system (or other electronic devices) to perform a process according to the present disclosure. A machine-readable medium includes any mechanism for storing information in a form (e.g., software, processing application) readable by a machine (e.g., a computer). The machine-readable medium may include, but is not limited to, magnetic storage medium, optical storage medium; magneto-optical storage medium, read only memory (ROM); random access memory (RAM); erasable programmable memory (e.g., EPROM and EEPROM); flash memory; or other types of medium suitable for storing electronic instructions.

Claim 1:
A computer-implemented method for avoiding obstacles (<NUM>) within a subterranean formation (<NUM>), the method
comprising:
receiving surface mapping data from one or more satellite images of an area of interest corresponding to the subterranean formation;
receiving surface topography data of the area of interest from one or more light detection and ranging , LIDAR, systems;
receiving an airborne gravity data set of the area of interest;
receiving a seismic data set of the area of interest;
identifying (<NUM>) a potential surface pad location using at least one of the surface mapping data, the surface topography data, the airborne gravity data set, or the seismic data set, the potential surface pad location including a surface hole for each of one or more wellbores (<NUM>);
generating (<NUM>) a resistivity survey for the potential surface pad location, the resistivity survey including at least one long line (<NUM>) extending through the surface hole for each of the one or more wellbores (<NUM>) and at least one short line (<NUM>) extending through the surface hole of one of the one or more wellbores (<NUM>), each short line intersecting the long line at the surface hole of one of the one or more wellbores (<NUM>); and
determining (<NUM>) whether one or more subsurface karst features are present within the subterranean formation disposed relative to at least one of the potential surface pad location or the one or more wellbores (<NUM>) using the resistivity survey.