A variety of magnetic ranging methods are used to determine distance and direction between a magnetic field sensor and a magnetic field source. If the sensor is in a near vertical hole, it may be difficult to orient the sensor's axes relative to known world coordinates, since no gravity high side is available. This can create difficulties calculating and applying ranging results. A magnetic azimuthal toolface may also be impaired due to magnetic interference. To address this problem, we combine and align ranging and gyro systems in one tool-string and use simultaneous gyro attitude measurements to define the orientation of a ranging system with respect to True North. We apply this technique to two distinct magnetic ranging methods. The first method consists of a solenoid based ranging system. The example shows how this method was used to drill a precisely parallel wellbore in a close proximity to a previously drilled vertical well. The second described method consists of an at-bit-while-drilling ranging system that was used to safely pass by a vertical well while drilling a horizontal well in a close proximity. The paper compares the results of alternative north orientation techniques for magnetic ranging versus the simultaneous gyro attitude referencing. The alternative techniques include a magnetic north orientation and the north orientation derived from a prior downhole survey and gravity high side tool face. The results show that the described technique can improve magnetic ranging accuracy by up to 10-fold over the previous methods. The paper provides 2D and 3D visualization and numerical analysis of the listed north orientation techniques applied to the magnetic ranging methods. Simultaneous gyro measurements can significantly improve magnetic ranging accuracy. The applications for the described technique include relief well drilling, plug and abandonment, collision avoidance/risk mitigation, civil and mining projects.

The development of heavy oil assets in Canada, and worldwide, often relies on Steam Assisted Gravity Drainage (SAGD). Directional drilling and surveying these horizontal wellbores presents a host of challenges to the service provider and operator alike. One such challenge relates to conventional surveying techniques and the cumulative errors associated with this approach. Once integrated over the length of the horizontal wellbore, downhole positional uncertainty can typically be 30 m or more in lateral uncertainty, and 5 m or more in vertical uncertainty. These errors present a number of complications in the development of the asset. To address the issue of cumulative uncertainty in horizontal wellbores, a method of absolute referencing to a surface generated magnetic signal has been developed and successfully deployed in the field. The surface installation is engineered to provide a precise location based on the measurable magnetic field for any point in a desired wellbore placement region. The surface installation consists of conductors arranged on surface above the intended well path, and the exact location of the installation is determined by way of a differential Global Positioning System (GPS) unit. While drilling, the installation is energized, and the Measurement While Drilling (MWD) tool samples the superimposed magnetic field vector. These results are transmitted to surface via standard real time telemetry, and a North, East and True Vertical Depth (TVD) position of the sensor is calculated via surface software in real time. The absolute positioning technique has been deployed on eight SAGD drilling wells at subsurface depths of 100 to 250 m, for two different operators in Northern Alberta, with encouraging results. On six of the eight wells, the calculated position of the sensor agreed with the integrated position as determined through standard MWD surveying. However, on two of the eight test wells, the absolute ranging determined position disagreed from the MWD integrated position by 10 m or more. The discrepancy observed could be accounted for by systematic errors in MWD surveying. Here we report in detail on a three well redrill program from this set. For shallow horizontal wellbores, the accuracy of the method described can be far superior to surveying techniques such as MWD or gyro at the end of the horizontal section, with estimated uncertainties that can be an order of magnitude smaller than the accumulated uncertainty associated with conventional methods. With non-cumulative uncertainty, the absolute positioning method can be used to complement SAGD drilling operations in a number of ways. Some potential uses of the technique include: no-access active wellbore twinning, vertical observation well avoidance, infill drilling, and TVD confirmation. Through these applications, it is predicted that operational costs at the rig site will be drastically reduced (via the elimination of wireline, tractor units and survey management techniques) and reservoir drainage will be better optimized by the deployment of the system.

Summary The growing problem of well-to-well fracture interactions in North American shale plays dictates the need for more accurate interlateral spacing measurements. Conventional wellbore surveying techniques, such as magnetic and gyroscopic measurements while drilling (MWD), cannot guarantee optimal placement due to growing systematic errors that dominate survey uncertainty. This uncertainty may impede optimal field stimulation modeling because the wellbore positioning data used in the analytical calculations are inaccurate. Multiple industry technical papers demonstrate a correlation between interlateral spacing and the severity of frac hits. The interlateral distance measurements are used in the calculations for optimal reservoir stimulation and frac hit modeling. With present commodity prices, the industry cannot afford suboptimal field development caused by inaccurate well placement. In this paper, we compare the conventional survey technique with a commercially proven long-distance active magnetic ranging system that supplements the traditional MWD system. We apply relevant survey error models to two exemplary well pads—an actual well pad from a West Texas shale play and a realistic, although hypothetical, example—and compare them with relative ranging uncertainty. The first example shows that MWD positional error exceeds relative ranging uncertainty while the wells are still near vertical at approximately 6,500 ft measured depth (MD). The second example shows that interlateral spacing uncertainty using active magnetic ranging can be 50% of the MWD semimajor error at the end of the curve at 10,000 ft MD [8,910 ft true vertical depth (TVD)] before the lateral section starts. The MWD uncertainty then gets larger due to systematic survey errors multiplied in the “dead reckoning” computation process. With the magnetic ranging applied while drilling, the ranging uncertainty stays practically the same throughout the whole well, enabling tenfold improvement in interlateral spacing accuracy.

The growing problem of well-to-well fracture interactions in North American shale plays dictates the need for more accurate inter-lateral spacing measurements. Conventional wellbore surveying techniques, such as magnetic or gyroscopic MWD and wireline measurements, cannot by themselves guarantee optimal placement due to systematic errors that dominate the uncertainty in well trajectory measurements. This uncertainty impedes optimal field stimulation and production modeling as the historical wellbore positioning data used in statistical analysis are inaccurate. With present commodity prices, the industry cannot afford suboptimal field development caused by inaccurate well placement. This paper is proposing the use of a commercially proven long-distance ranging system to minimize inter-well uncertainty for optimizing production development in shale plays. The solution to the conventional survey uncertainty problem is to measure relative well-to-well position using a long-distance at-bit while drilling magnetic ranging system. The system consists of a highly sensitive alternating magnetic field receiver assembly in the adjacent well and a magnetic field source in the form of a magnetic bit sub in the drilling well BHA. The bit sub includes permanent rare earth magnets and generates a sinusoidal magnetic field when it is being rotated by the flow of drilling fluid through the mud motor or when the entire drillstring is rotated. The system does not replace conventional MWD sensors and requires standard survey data for calculating ranging results. These results are available live for realtime directional drilling decision making. In this paper, we analyze the accuracy of the system in related downhole projects. The system surface test results agree with the accuracy of 5% of the distance between the drilling well and the offset well. This is a many-fold improvement in comparison to traditional surveying methods applied to a typical lateral well profile. The system has already been used on several projects of a similar nature and proved its effectiveness. The suggested methodology can identify the cause of interactions between wellbores due to proximity, which allows operators to implement measures to improve hydrocarbon recovery and mitigate financial losses from "frac hits". The described technique eliminates the major part of the uncertainty in lateral spacing and therefore allows increased accuracy for reservoir stimulation and production modeling. The concept of relative position measurements using magnetic ranging methods has been around for a long time and has helped to avoid well collisions, create twinned wellbore pairs or intercept wells in the relief well, and for complex plug and abandonment applications. The purpose of this paper is to raise the attention of the industry to the described technique so the advantages of relative well placement can be applied for a better understanding of the growing problem of "frac hits" in North American shale plays.