All-Attitude Gyro While Drilling Technology Provides Accurate Surveys in High Angle East/West Directional Wellbores Delivering Reduced Costs and Increasing the Length of the Producing Zone
The accurate placement of directionally controlled wellbores is essential in order to maximize oil production while avoiding collisions with existing wells. Error models provide estimates of the positional uncertainty that can be expected when using a specific survey tool. For example, a Measurement While Drilling (MWD) tool will have a different ellipsoid of uncertainty when compared to a Gyro While Drilling (GWD) or a continuous gyro tool. Whichever survey tool is chosen, the uncertainty in the calculated wellbore position is dependent on the trajectory and latitude of the planned wellbore. Many drilling projects have been designed assuming specific survey instruments and favorable drilling directions. However, these assumptions are often not fulfilled due to existing wellbores, environmental safety concerns, land management issues, drilling costs and survey tools available. Different azimuthal corrections and methods of surveying have been deployed to increase confidence in the wellbore placement when drilling wells in east or west directions at high inclinations. MWD surveys with magnetic interference corrections and rate-gyro surveying on wireline are two examples of these methods. Previous GWD technology was limited to 70 degrees of inclination and was not an option for high angle and horizontal wells. With the development of an all-attitude GWD tool, it is now possible to provide accurate gyroscopic surveys at all inclinations and all directions during the drilling process in real time.
This paper describes a case study in which the all-attitude GWD tool was utilized to achieve tighter control of well trajectories drilled predominantly in an easterly direction in close proximity to a number of existing wellbores. This approach allowed a significant reduction in costs since it became possible to drill all the wells from an existing pad and so avoid land management and environmental concerns initially associated with the project. Further, the accuracy of an all-attitude GWD tool allowed the operator to drill safely through an additional 1,000 feet of geological pay zone, a result that could not have been achieved safely using MWD surveys alone.