Method and system for automated adjustment of drilling mud properties

Abstract

Drilling mud properties in a mud recirculation system ( 13 ) of an oil and/or gas well drilling assembly ( 1 ) are automatically adjusted by an automated mud treating assembly ( 20,25 ) that is governed hierarchal primary and secondary optimization and control loops ( 30,31 ) that continuously keep the density, viscosity, pH and other mud properties within specifications set by a model-based tertiary optimization and control loop to ensure that the mud properties will lead to sufficient drilled cutting transport, borehole stability, drill bit hydraulics, and minimum friction torque and drag.

1 . A method for automated adjustment of drilling mud properties in a mud recirculation system of a rig for drilling an underground wellbore, the method comprising inducing hierarchal primary and secondary optimization and control loops to adjust injection rates of mud additives into a circulated mud stream flowing through an automated mud treating assembly, to continuously keep mud properties, comprising density, viscosity, pH and optionally other mud properties, within specifications set by a model-based tertiary optimization and control loop. 
     
     
         2 . The method of  claim 1 , wherein the primary optimization and control loop governs opening and closing of additive injection control valves of the automated mud treating assembly to meet injection rates of each additive set by set by the secondary optimization and control loop that is connected to the tertiary optimization and control loop that determines the appropriate ranges or setpoints for the mud properties in order to meet multiple operational objectives, such as maximizing cutting transport capabilities of the drilling mud and maintaining wellbore mechanical stability. 
     
     
         3 . The method of  claim 1 , wherein the mud properties are measured by a sensor assembly that measures the mud properties of the mud in the mud recirculation system at the rig upstream and/or downstream of the automated mud treating assembly. 
     
     
         4 . The method of  claim 3 , wherein the sensor assembly comprises an upstream sensor assembly comprising primary and secondary untreated mud flux property sensors for monitoring the properties of the untreated mud flowing from a cuttings removal system to the automated mud treating assembly, wherein the primary untreated mud flux property sensor is arranged in the mud recirculation system between the secondary untreated mud flux property sensor and the mud treating assembly. 
     
     
         5 . The method of  claim 1 , wherein:
 the primary, secondary and tertiary optimization and control loops operate at different time scales and hierarchies;   the tertiary optimization and control loop is the master of the secondary optimization and control loop and operates at the highest time scale or lower sampling rate; and   the secondary optimization and control loop is governed by the tertiary optimization and control loop and operates at the lower time scale or higher sampling rate than the tertiary optimization and control loop but higher time scale and lower sampling rate than the primary optimization and control loop which is governed by the secondary optimization and control loop.   
     
     
         6 . The method of  claim 4 , wherein the sensor assembly further comprises a downstream sensor assembly comprising primary and secondary treated mud property sensors for measuring at least one of the group consisting of: density, viscosity, pH and other properties,. of the treated mud in the mud recirculation system at the rig downstream of the mud treating assembly, wherein the primary treated mud flux property sensor is arranged in the mud recirculation system between the mud treating assembly and the secondary treated mud property sensor; and wherein:
 the primary optimization and control loop is connected to a sensor assembly that measures the actual injection rate of each additive in the automated mud treating assembly;   the secondary optimization and control loop is connected to the sensor assembly that measures the primary untreated and treated mud properties;   the tertiary optimization and control loop is connected to the primary untreated mud sensor assembly and optionally to the secondary untreated mud sensor assembly.   
     
     
         7 . The method of  claim 4 , wherein the primary treated mud flux property sensor forms part of the secondary optimization and control loop and the secondary treated mud flux property sensor forms part of the tertiary optimization and control loop. 
     
     
         8 . The method of  claim 1 , wherein the tertiary optimization and control loop comprises an optimization module that determines the ranges or the setpoints of the primary treated mud properties given the objective functions of the tertiary optimization and control loop such as ensuring sufficient cutting transport, wellbore mechanical stability and estimates of:
 a) drill string torque and drag;   b) borehole stability and permeability;   c) size, volume, weight, density and composition of drill cuttings; and   d) downhole mud velocity, pH, viscosity, density and composition.   
     
     
         9 . The method of  claim 8 , wherein the ranges of the mud property values as determined by the optimization module are included as the desired ranges to be honored by a multivariable control algorithm in the secondary control loop. 
     
     
         10 . The method of  claim 9 , wherein the multivariable control algorithm is a Model Predictive Controller (MPC) algorithm that casts the multivariable control problem as an optimal control problem with an objective function of minimizing the deviation of the primary treated mud properties from the desired ranges given the minimum and maximum amount of additives to be added at each cycle and the models between mud properties to be controlled and additives as well as the drilling and mud flux circulation rates. 
     
     
         11 . The method of  claim 10 , wherein the multivariable control algorithm is provided with models identifying mathematical relationships between the additives, mud properties and measured variations in drilling rates that affect variations in drill cuttings concentration. 
     
     
         12 . A system for automated adjustment of drilling mud properties in a mud recirculation system of a rig for drilling an underground wellbore, the system comprising hierarchal primary and secondary optimization and control loops to adjust injection rates of mud additives into a mud circulation conduit in an automated mud treating assembly, arranged to continuously keep mud properties, comprising density, viscosity, pH, within specifications set by a model-based tertiary optimization and control loop. 
     
     
         13 . The system of  claim 12 , wherein the primary optimization and control that governs opening and closing of the additive control valves of the automated mud treating assembly, to meet the injection rates of each additive set by set by the secondary optimization and control loop that is connected to the tertiary optimization and control loop that determines the appropriate ranges or setpoints for the mud properties in order to meet multiple operational objectives, such as maximizing cutting transport capabilities of the drilling mud and maintaining wellbore mechanical stability. 
     
     
         14 . The system of  claim 12 , wherein the system comprises a sensor assembly that measures the mud properties of the mud in the mud recirculation system at the rig upstream and/or downstream of the automated mud treating assembly. 
     
     
         15 . The system of  claim 12 , wherein the mud treating assembly comprises an additives and mud mixing tank, the size of which is determined by two aspects:
 the minimum residence time required by the characteristics of the drilling mud to ensure a homogeneous mixture when additives are added; and   the balance between the response time required by the secondary multivariable control loop to bring the properties of the primary untreated mud to the desired values or ranges while ensuring that the addition of the additives as the result of the controller's actions does not lead to major fluctuations in the steady state or transient values of the primary treated and secondary untreated mud properties.   
     
     
         16 . The system of  claim 12 , wherein said hierarchal primary and secondary optimization and control loops are additionally arranged to continuously keep other mud properties within specifications set by the model-based tertiary optimization and control loop. 
     
     
         17 . The method of  claim 1 , wherein additionally inducing said hierarchal primary and secondary optimization and control loops to continuously keep other mud properties within specifications set by the model-based tertiary optimization and control loop.