Directional drilling with automatic uncertainty mitigation

Abstract

A disclosed drilling system includes a drill string assembly having subsystem inputs that control ROP and other performance parameters; and a processing system that provides automated uncertainty mitigation of a model for controlling the subsystem inputs. The drilling string assembly may include a BHA subsystem and a drill string that connects the BHA to a drilling rig subsystem and a fluid circulation subsystem. The processing system operates by: obtaining a drilling system model having interaction states representing how each subsystem input impacts the subsystem; characterizing an uncertainty for each interaction state; evaluating an influence of each interaction state's uncertainty on the performance parameters; calculating a net benefit for mitigating said model uncertainties; automatically mitigating said one or more model uncertainties when the net benefit exceeds a threshold, thereby improving the model of the drilling system; and controlling the subsystem inputs based on the model.

1 . A drilling method that comprises:
 obtaining a model of a drilling system having subsystem inputs that control one or more performance parameters of the drilling system, said model having interaction states that each represent one of said subsystem input's impact on a subsystem of the drilling system;   estimating a probability distribution of a model uncertainty for each interaction state;   evaluating an influence of each interaction state's model uncertainty on each of said performance parameters;   calculating a net benefit for mitigating one or more of said model uncertainties;   automatically mitigating said one or more model uncertainties when the net benefit exceeds a threshold, thereby improving the model of the drilling system; and   controlling the drilling system based on the model.   
     
     
         2 . The method of  claim 1 , wherein the model further accounts for subsystem input uncertainties and performance parameter measurement uncertainties. 
     
     
         3 . The method of  claim 2 , wherein the model is expressible as
     x′   ij =( a   ij +Δ ij ) x   ij   +b   ij   u   j   +v   ij  
       y   i =Σ j   y   ij   +w   i =Σ j   c   ij   x   ij   +w   i  
   
       where j is the subsystem input index, u j  is the subsystem input, i is the performance parameter index, y i  is the performance parameter, x ij  is the interaction state, v ij  is the subsystem input uncertainty, Δ ij  is the interaction model uncertainty, w i  is the performance parameter measurement uncertainty, and model coefficients are a ij , b ij , and c ij . 
     
     
         4 . The method according to  claim 1 , wherein said performance parameters comprise one or more of: rate of penetration (ROP); circulation efficiency, bottomhole pressure, drilling path error, and bit wear. 
     
     
         5 . The method according to  claim 1 , wherein the subsystem inputs include one or more of: hook load, topdrive torque, rotation rate (RPM), pump rate, pump pressure, choke opening, tool face orientation, and fluid viscosity. 
     
     
         6 . The method according to  claim 1 , wherein said net benefit accounts for performance parameter degradation during a mitigation process and duration of the mitigation process. 
     
     
         7 . The method of  claim 6 , wherein said net benefit further accounts for achievable performance parameter improvements. 
     
     
         8 . The method of  claim 7 , wherein the achievable performance parameter improvements are determined based on maintaining a margin of stability. 
     
     
         9 . The method according to  claim 1 , wherein the threshold is zero. 
     
     
         10 . A drilling system that comprises:
 a drilling assembly having subsystem inputs that control one or more performance parameters of the drilling system, the drilling assembly including:
 a bottomhole assembly (BHA) subsystem with a steerable drill bit; and 
 a drill string that connects the BHA subsystem to a drilling rig subsystem and a fluid circulation subsystem; and 
   a processing system that provides automated uncertainty mitigation of a model for controlling the drilling assembly by:
 obtaining a model of the drilling system, said model having interaction states that each represent an impact of one of said subsystem inputs on one of: the BHA subsystem, the drilling rig subsystem, and the fluid circulation subsystem; 
 estimating a probability distribution of a model uncertainty for each interaction state; 
 evaluating an influence of each interaction state's model uncertainty on each of said performance parameters; 
 calculating a net benefit for mitigating one or more of said model uncertainties; 
 automatically mitigating said one or more model uncertainties when the net benefit exceeds a threshold, thereby improving the model of the drilling system; and 
 controlling the subsystem inputs based on the model. 
   
     
     
         11 . The system of  claim 10 , wherein the model further accounts for subsystem input uncertainties and performance parameter measurement uncertainties. 
     
     
         12 . The system of  claim 11 , wherein the model is expressible as
     x′   ij =( a   ij +Δ ij ) x   ij   +b   ij   u   j   +v   ij  
       y   i =Σ j   y   ij   +w   i =Σ j   c   ij   x   ij   +w   i  
   
       where j is the subsystem input index, u j  is the subsystem input, i is the performance parameter index, y i  is the performance parameter, x ij  is the interaction state, v ij  is the subsystem input uncertainty, Δ ij  is the interaction model uncertainty, w i  is the performance parameter measurement uncertainty, and model coefficients are a ij , b ij , and c ij . 
     
     
         13 . The system according to  claim 10 , wherein said performance parameters comprise one or more of: rate of penetration (ROP); circulation efficiency, bottomhole pressure, drilling path error, and bit wear. 
     
     
         14 . The system according to  claim 10 , wherein the subsystem inputs include one or more of: hook load, topdrive torque, rotation rate (RPM), pump rate, pump pressure, choke opening, tool face orientation, and fluid viscosity. 
     
     
         15 . The system according to  claim 10 , wherein said net benefit accounts for performance parameter degradation during a mitigation process and duration of the mitigation process. 
     
     
         16 . The system of  claim 15 , wherein said net benefit further accounts for achievable performance parameter improvements. 
     
     
         17 . The system of  claim 16 , wherein the achievable performance parameter improvements are determined based on maintaining a margin of stability. 
     
     
         18 . The system according to  claim 10 , wherein the threshold is zero.