Surface control system adaptive downhole weight on bit/torque on bit estimation and utilization

An apparatus, comprising:

• a surface differential pressure sensor configured to sense a surface differential pressure;
• and
• a controller configured to:
• receive, from a bottom hole assembly (BHA), a coefficient representing a determined relationship between a downhole differential pressure and a downhole weight on bit (WOB), the coefficient being received in response to a difference between the coefficient and a prior coefficient being greater than a threshold value, the prior coefficient comprising a relationship between a prior downhole differential pressure and a prior downhole WOB;
• implement, in an autodriller feedback loop, the coefficient;
• input the surface differential pressure from the surface differential pressure sensor into the autodriller feedback loop implementing the coefficient;
• estimate a WOB based on the surface differential pressure input into the autodriller feedback loop;
• and
• control a drill string based on the estimated WOB in the autodriller feedback loop.

A non-transitory machine-readable medium having stored thereon machine-readable instructions executable to cause a machine to perform operations comprising:

• receiving, from a bottom hole assembly (BHA), a coefficient representing a determined relationship between a downhole differential pressure and a downhole weight on bit (WOB), the coefficient being received in response to a difference between the coefficient and a prior coefficient being greater than a threshold value, the prior coefficient representing a relationship between a prior downhole differential pressure and a prior downhole WOB;
• estimating a surface WOB based on a surface differential pressure input into an autodriller feedback loop implementing the coefficient;
• determining a ratio between the surface WOB of a drill string, applied in response to a set rate of penetration (ROP), and the downhole WOB;
• determining a change value of the ratio;
• and
• adjusting the set ROP in response to the change value of the ratio becoming a negative value until the change value of the ratio reaches a zero or positive value.