Multishot Survey: Film and Solid-State Inclination Recording, Magnetic Versus Gyro Tools, and Bottomhole Location in Deviated WCSB Wells

A multishot survey is a directional measurement technique that records the inclination and azimuth of a wellbore at many depths during a single run, producing a continuous picture of the path the hole has taken from surface to total depth. It is the multi-reading counterpart to the single-shot survey, which captures only one station per trip. The original tools were photographic: a compass and pendulum-style inclination unit were photographed by a small camera whose film advanced automatically at preset time intervals, so as the instrument was pulled or run through the drillstring it exposed a strip of frames, each frame stamped with a clock-synchronized depth. Modern multishot instruments replace film with solid-state accelerometers and magnetometers that log digitally, but the operating principle and the name have survived. The defining value of a multishot is accuracy across the whole borehole rather than at a single station: by stacking dozens of inclination and direction readings, a directional engineer can compute the true three-dimensional trajectory and, critically, the bottomhole location relative to the surface. That bottomhole position matters for hitting a geological target, for honouring lease and spacing boundaries, and for proving that a horizontal leg stayed inside the intended formation window. Magnetic multishot tools read direction from the earth's magnetic field, so they must run inside non-magnetic drill collars, usually monel, to avoid interference from the steel string, and their azimuth must later be corrected for magnetic declination and drillstring interference. Where magnetic readings are unreliable, near casing, in steel-congested fields, or at high latitude, a gyroscopic multishot is used instead because it references true north mechanically rather than magnetically. In the Western Canadian Sedimentary Basin, multishot surveys underpin the directional control of the long horizontal wells that define Montney, Duvernay, and Cardium development, and they connect directly to the concepts of inclination, azimuth, measurement while drilling, and the dogleg severity that constrains how sharply a well can be steered. Although measurement-while-drilling now provides real-time directional data on most rigs, the standalone multishot remains a definitive, independent openhole record used to verify the MWD-derived trajectory or to survey a hole where MWD was not run.

Film Strip Versus Solid-State Recording

The classic magnetic multishot used a roll of film advanced by a clock-driven mechanism that exposed one frame at each preset interval. As the tool moved through the hole, each frame photographed a compass card and an inclination pendulum, and the operator later matched frame numbers to a depth-versus-time log to assign a depth to every reading. Solid-state multishot tools have largely replaced film: triaxial accelerometers measure inclination from the gravity vector and triaxial magnetometers measure azimuth, with readings written to memory and downloaded after the run. The accuracy and density of stations improved, but the workflow concept, recording many stations and reconciling them to depth, is unchanged. The film tool is still encountered on older equipment and in training references that explain why the method is called a multishot.

Drop Survey and Go-Devil Deployment

A common way to run a magnetic multishot is the drop, or go-devil, method, where the survey instrument is dropped down the drillpipe and lands in a non-magnetic collar near the bit. The crew then pulls the string in stands, pausing at each connection so the tool records a station at a known depth before the next stand comes off. This in-string technique surveys the hole during a normal trip out, adding little rig time, which is why it remains economical in the WCSB even alongside MWD. After retrieval, the memory is downloaded, declination and interference corrections are applied, and the minimum-curvature method is used to compute the dogleg severity and bottomhole coordinates from the station list.

Related Terms

A multishot survey produces, at each station, a measured inclination and azimuth, the two angles that define hole orientation. Stacking those stations and applying the minimum-curvature calculation yields dogleg severity, the rate of trajectory change that limits how aggressively a well can be steered and how much fatigue the drillstring will see. On most modern wells the multishot complements measurement while drilling, which supplies the same angles in real time, so the two methods are best understood as independent measurements of one trajectory used to cross-check each other.

Real-World WCSB Scenario: Verifying a Duvernay Horizontal Near Fox Creek

An operator drilling a 3,000 m measured-depth Duvernay horizontal near Fox Creek runs MWD throughout the lateral, but the geosteering log suggests the toe may have drifted high out of the target shale into an overlying carbonate. To settle the question before fracturing, the operator drops a gyroscopic multishot on the trip out, surveying every stand from total depth back through the cased build section. The gyro run costs roughly 28,000 CAD plus a few hours of rig time at about 38,000 CAD per day.

The independent gyro survey confirms the MWD azimuth was biased by drillstring interference near the heel, and the as-drilled bottomhole location is 14 m updip of the MWD estimate. The corrected trajectory shows two stages would have been placed in non-reservoir rock; the operator skips those perforation clusters, saving about 220,000 CAD in completion cost on unproductive intervals.