Optimized coiled tubing string design and analysis for extended reach drilling

A system for optimizing coiled tubing string configurations for drilling operations, the system comprising:

• a coiled tubing string to drill a wellbore along a planned trajectory through a subsurface formation, the coiled tubing string having a non-rotatable segment and a rotatable segment, the non-rotatable segment extending from a surface of the wellbore and attaching to a downhole motor at a proximal end of the rotatable segment within the wellbore;
• a surface pump coupled to a proximal end of the coiled tubing string to inject drilling fluid into the wellbore as it is drilled along the planned trajectory;
• and
• a control system coupled to the coiled tubing string and the surface pump to perform a plurality of functions, including functions to:
• determine physical properties of the coiled tubing string, the physical properties including at least one of a weight of the coiled tubing string or a torsional yield strength of tubing material associated with each segment of the coiled tubing string;
• estimate a length of the non-rotatable segment of the coiled tubing string for drilling one or more sections of the wellbore along the planned trajectory, based on the physical properties of the coiled tubing string corresponding to the non-rotatable segment;
• calculate pressure drop values for a plurality of points of interest along the coiled tubing string excluding the downhole motor and the rotatable segment, based on a capacity of the surface pump to inject the drilling fluid into the wellbore and the estimated length of the non-rotatable segment of the coiled tubing string;
• estimate a length of the rotatable segment of the coiled tubing string within the one or more sections of the wellbore to be drilled, based on the calculated pressure drop values and the physical properties of the coiled tubing string corresponding to the rotatable segment;
• and
• control one or more operating parameters of the coiled tubing string while drilling the one or more sections of the wellbore through the subsurface formation, based on the estimated lengths of the respective non-rotatable and rotatable segments of the coiled tubing string, the operating parameters including a rotation rate of the rotatable segment and a flow rate of the drilling fluid injected by the surface pump.

A computer-readable storage medium having instructions stored therein, which when executed by a computer cause the computer to perform a plurality of functions, including functions to:

• determine physical properties of a coiled tubing string for a wellbore to be drilled along a planned trajectory through a subsurface formation, the coiled tubing string having a non-rotatable segment and a rotatable segment, the non-rotatable segment extending from a surface pump into the wellbore and attaching to a downhole motor at a proximal end of the rotatable segment within the wellbore, and the physical properties including at least one of a weight of the coiled tubing string or a torsional yield strength of tubing material associated with each segment of the coiled tubing string;
• estimate a length of the non-rotatable segment of the coiled tubing string within one or more sections of the wellbore to be drilled along the planned trajectory, based on the physical properties corresponding to the non-rotatable segment;
• calculate pressure drop values for a plurality of points of interest along the coiled tubing string excluding the downhole motor and the rotatable segment, based on a capacity of the surface pump to inject drilling fluid into the wellbore and the estimated length of the non-rotatable segment of the coiled tubing string;
• estimate a length of the rotatable segment of the coiled tubing string within the one or more sections of the wellbore to be drilled, based on the calculated pressure drop values and the physical properties of the coiled tubing string corresponding to the rotatable segment;
• and
• control one or more operating parameters of the coiled tubing string while drilling the one or more sections of the wellbore through the subsurface formation, based on the estimated lengths of the respective non-rotatable and rotatable segments of the coiled tubing string, the operating parameters including a rotation rate of the rotatable segment and a flow rate of the drilling fluid injected by the surface pump.