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Summary A new method has been developed that provides an innovative solution to problems commonly associated with conventional land seismic surveying. “Stakeless surveying” dramatically improves operational procedures by eliminating the need for stakes and flagging while providing a higher level of positional accuracy for each seismic point. Using this technique requires some modification to receiver deployment and source navigation procedures. This technology provides multiple benefits without increasing program costs. Introduction Surveying has long been an important component of 3D seismic acquisition. While survey methods have evolved with improvements in technology, the standard technique has been to mark points with stakes and/or flagging prior to recording operations. This leads to numerous problems resulting from the time lag between surveying and recording. Problems with Conventional Methods of Seismic Surveying The 3D seismic technique on land requires locating and surveying numerous source and receiver positions on the ground. The point markers are usually required to remain on the ground for long periods of time before being utilized. This often results in missing, damaged or hard to find markers due to various circumstances including: Inclement weather conditions Livestock and/or wildlife feeding Agricultural activity Cyclic vegetation growth On lands administered by the U. S. Bureau of Land Management (BLM), source line surveying is required months ahead of seismic recording to allow time for completing an archeological assessment. In extreme cases, survey crews must revisit the project area to refresh flagging and stakes, resulting in additional costs and interfering with scheduling. In addition to these problems, there are positioning issues that impact data accuracy. Theoretically, seismic energy originates from a source point (drill hole or center of vibrator array) and is recorded at a receiver point (center of geophone array). These points are often not equivalent to the locations surveyed. Reasons for this include: Heliportable or heavily-wooded operations Weather conditions may cause the relocation of vibrator points Vibrators often have to be offset from a point so vibrator operators can see the stake (figure 1) Permit conditions may change Receiver arrays may not be properly positioned in conditions of rough terrain or heavy vegetation Several of these conditions require undesirable resurveying, increasing the likelihood of scheduling problems and data errors. After the recording phase of the project is completed, all stakes and flagging used on the program must then be retrieved and transported offsite. This method of conducting a separate survey and seismic recording effort results in two unrelated sets of data that require integration in the processing center. Stakeless Survey Method A solution to many of the issues presented is surveying simultaneously with drilling or recording operations. This eliminates the need for stakes or flagging, provides more accurate positioning of seismic points and increases productivity. By combining Global Positioning System (GPS), Geographic Information System (GIS) and navigation technology into a system for seismic acquisition, a robust solution is created. Stakeless Source Operations For vibrator operations, each unit is equipped with a GPS receiver and a computer-based navigation system.
- Energy > Oil & Gas > Upstream (1.00)
- Government > Regional Government > North America Government > United States Government (0.54)
- North America > United States > Wyoming > Green River Basin (0.99)
- North America > United States > Utah > Green River Basin (0.99)
Summary With the ever increasing complexity of land seismic acquisition and stringent regulations imposed in downstream field development, the ability to model or otherwise visualize the project area significantly contributes to the success of the project. Airborne Light Detection and Ranging (LiDAR) is an emerging technology that provides a highly accurate, high-resolution representation of the earth’s surface. It is a tool that provides valuable information of the terrain and vegetative canopy conditions. The application of products derived from LiDAR can provide significant benefits throughout the seismic acquisition and front-end processing, and field development phases of a project. Operational cost savings can be realized through source position “pre-planning”, elevation substitution, identification of drill-pad sites, planning of flow-line/pipeline placement and road access. Additionally, HSE issues are improved by pre-planning emergency response plans, minimizing the number of field crew on the ground and time in the field. LiDAR Basics LiDAR is a remote sensing technology that provides high precision geo-referenced elevation data that is used for creating digital elevation models (DEM’s) for a wide range of applications. The LiDAR system is the integration of three components: a laser scanner, a Global Positioning System (GPS receiver), and an Inertial Measurement Unit (IMU). The laser scanner, mounted onto an aircraft, emits optical pulses at a rate of 20,000-100,000 pulses per second. The light is transmitted from the aircraft to a surface and the energy is reflected back to the sensor where the travel time is recorded. The velocity of the pulse is equal to the speed of light and the two-way travel time is easily converted to distance (range). The laser is aimed at a rotating mirror, inside the aircraft, that spreads the pulses along a path perpendicular to the line of flight, generating a swath of data points. The laser scanner records the scan angle, intensity, and travel time of each pulse before the emission of the next pulse. The GPS receiver is the component of the LiDAR system that provides the absolute spatial position of the sensor. Applying a geometric principle known as 3-D trilateration, the GPS receiver can deduce its own position using the signals from 4 or more Earthorbiting satellites. There are, however, inherent errors in the GPS positions due mainly to atmospheric conditions, satellite orbits, and GPS receiver noise. These errors can be accounted for using Differential GPS (DGPS): by positioning a GPS base station over a known control point and comparing the x,y,z of this known position to the position derived from the satellite data. This solution is then applied to the airborne GPS receiver. The base station should be placed within a 25 mile radius so that errors related to DGPS positioning are mitigated. The third component is the IMU which measures the orientation of the LiDAR system by recording the attitude of the aircraft (i.e. pitch, roll, and heading) (Figure 1). The airborne LiDAR system allows for rapid acquisition of very accurate high-resolution topographic data with x,y,z point densities ranging from 1-20 points/m2, vertical and horizontal accuracies on the order of 10-30 cm (4-12 in.) and 30-50 cm (12-20 in.), respectively.
- North America > United States > Wyoming > Green River Basin (0.99)
- North America > United States > Utah > Green River Basin (0.99)