Assessing curability in lost circulation events

Abstract

A method for characterizing a subsurface interval where drilling fluid is being lost includes receiving surface drilling values captured while drilling a wellbore through the subsurface interval. The method also includes analyzing the surface drilling values and identifying on-bottom surface drilling values and on-bottom mechanical specific energy (MSE) values. The method also includes identifying a first changepoint in the on-bottom surface drilling values. The method also includes identifying a second changepoint in the on-bottom MSE values. The method also includes determining a cause of a lost circulation event in the subsurface interval based upon the first and second changepoints.

What is claimed is: 
     
         1 . A method for characterizing a subsurface interval where drilling fluid is being lost, the method comprising:
 receiving surface drilling values captured while drilling a wellbore through the subsurface interval;   analyzing the surface drilling values and identifying on-bottom surface drilling values and on-bottom mechanical specific energy (MSE) values;   identifying a first changepoint in the on-bottom surface drilling values;   identifying a second changepoint in the on-bottom MSE values; and   determining a cause of a lost circulation event in the subsurface interval based upon the first and second changepoints.   
     
     
         2 . The method of  claim 1 , wherein the surface drilling values comprise a plurality of surface weight on bit (SWOB) values, a plurality of surface torque (STOR) values, and a plurality of standpipe pressure (SPPA) values, wherein downhole drilling values are determined based upon the surface drilling values, and wherein the downhole drilling values comprise a plurality of downhole WOB values and a plurality of downhole torque values that are based upon the SWOB values and the STOR values. 
     
     
         3 . The method of  claim 2 , wherein MSE values are determined based upon the downhole drilling values, and wherein the MSE values provide an estimate of an amount of energy to drill through a unit of rock in the subsurface interval. 
     
     
         4 . The method of  claim 1 , wherein the on-bottom surface drilling values comprise a subset of the surface drilling values that occurs while a drill bit is on-bottom in the wellbore. 
     
     
         5 . The method of  claim 4 , wherein the on-bottom MSE values comprise a subset of the MSE values that occur while the drill bit is on-bottom in the wellbore. 
     
     
         6 . The method of  claim 1 , wherein the first changepoint is greater than a first threshold, and wherein the second changepoint is greater than a second threshold. 
     
     
         7 . The method of  claim 1 , wherein the first changepoint is identified in on-bottom standpipe pressure (SPPA) measurements that comprise a subset of the surface drilling values that occur while a drill bit is on-bottom in the wellbore. 
     
     
         8 . The method of  claim 1 , further comprising:
 identifying a portion of the subsurface interval based upon the first changepoint and the second changepoint; and   displaying the portion of the subsurface interval, the cause of the lost circulation event, or both.   
     
     
         9 . The method of  claim 8 , further comprising determining whether the cause is curable. 
     
     
         10 . The method of  claim 9 , further comprising performing a lost circulation mitigation action in the wellbore adjacent to the portion of the subsurface interval in response to determining that the cause is curable. 
     
     
         11 . A computing system, comprising:
 one or more processors; and   a memory system comprising one or more non-transitory computer-readable media storing instructions that, when executed by at least one of the one or more processors, cause the computing system to perform operations, the operations comprising:
 receiving surface drilling values captured while drilling a wellbore through a subsurface interval; 
 analyzing the surface drilling values and identifying on-bottom surface drilling values and on-bottom mechanical specific energy (MSE) values; 
 identifying a first changepoint in the on-bottom surface drilling values; 
 identifying a second changepoint in the on-bottom MSE values; 
 identifying a first portion of a subsurface interval based upon the first changepoint and the second changepoint; and 
 determining a cause of a lost circulation event in the wellbore based upon the first portion of the subsurface interval. 
   
     
     
         12 . The computing system of  claim 11 , wherein the surface drilling values comprise a plurality of surface weight on bit (SWOB) values, a plurality of surface torque (STOR) values, and a plurality of standpipe pressure (SPPA) values, wherein downhole drilling values are determined based upon the surface drilling values, wherein the downhole drilling values comprise a plurality of downhole WOB values and a plurality of downhole torque values that are based upon the SWOB values and the STOR values, wherein MSE values are determined based upon the downhole drilling values, and wherein the MSE values provide an estimate of an amount of energy to drill through a unit of rock in the subsurface interval. 
     
     
         13 . The computing system of  claim 11 , wherein the operations further comprise:
 forecasting a plurality of forecasted surface drilling values based upon the surface drilling values, wherein each of the forecasted surface drilling values occurs at a same time as one of the on-bottom surface drilling values;   identifying the on-bottom surface drilling values that are lower than their corresponding forecasted surface drilling values, which represent second negative anomalies that indicate second drilling breaks that are conductive to a drilling fluid;   forecasting a plurality of forecasted MSE values based upon the on-bottom MSE values, wherein each of the forecasted MSE values occurs at a same time as one of the on-bottom MSE values; and   identifying the on-bottom MSE values that are lower than their corresponding forecasted MSE values, which represent first negative anomalies that indicate first drilling breaks.   
     
     
         14 . The computing system of  claim 13 , wherein the first portion of the subsurface interval is also based upon the on-bottom surface drilling values that are lower than their corresponding forecasted surface drilling values, and the on-bottom MSE values that are lower than their corresponding forecasted MSE values, and wherein the first portion of the subsurface interval corresponds to a first portion of a rock with mechanical properties below a predetermined mechanical property threshold. 
     
     
         15 . The computing system of  claim 14 , wherein the operations further comprise identifying a second portion of the subsurface interval based upon the first changepoint, the second changepoint, the on-bottom surface drilling values that are lower than their corresponding forecasted surface drilling values, and the on-bottom MSE values that are lower than their corresponding forecasted MSE values, wherein the second portion of the subsurface interval corresponds to a second portion of the rock that is conductive to the drilling fluid, and wherein the cause of the lost circulation event is also determined based upon the second portion of the subsurface interval. 
     
     
         16 . A non-transitory computer-readable medium storing instructions that, when executed by one or more processors of a computing system, cause the computing system to perform operations, the operations comprising:
 receiving surface drilling values captured while drilling a wellbore through a subsurface interval, wherein the surface drilling values comprise standpipe pressure (SPPA) values;   identifying on-bottom surface drilling values based upon the surface drilling values, wherein the on-bottom surface drilling values comprise on-bottom SPPA values based upon the SPPA values, which represent a subset of the SPPA values that occurs while a drill bit is on-bottom in the wellbore;   identifying on-bottom mechanical specific energy (MSE) values based upon the surface drilling values;   identifying first changepoints in the on-bottom surface drilling values that are greater than a first threshold, wherein the first changepoints are identified in the on-bottom SPPA values;   identifying second changepoints in the on-bottom MSE values that are greater than a second threshold; and   determining a cause of a lost circulation event based upon the first and second changepoints.   
     
     
         17 . The non-transitory computer-readable medium of  claim 16 , wherein the surface drilling values also comprise surface weight on bit (SWOB) values and surface torque (STOR) values, wherein downhole drilling values are determined based upon the surface drilling values, wherein the downhole drilling values comprise downhole WOB values and downhole torque values, wherein the downhole WOB values and the downhole torque values are based upon the SWOB values and the STOR values, wherein MSE values are determined based upon the downhole drilling values, wherein the MSE values are based upon the downhole WOB values and the downhole torque values, and wherein the MSE values provide an estimate of an amount of energy to drill through a unit of rock in the subsurface interval. 
     
     
         18 . The non-transitory computer-readable medium of  claim 16 , wherein the operations further comprise:
 forecasting forecasted SPPA values based upon the on-bottom SPPA values, wherein each of the forecasted SPPA values occurs at a same time as one of the on-bottom SPPA values;   identifying the on-bottom SPPA values that are lower than their corresponding forecasted SPPA values, which represent first negative anomalies that indicate first drilling breaks that are conductive to drilling fluid, wherein a first portion of the subsurface interval and a second portion of the subsurface interval are also identified based upon the on-bottom SPPA values that are lower than their corresponding forecasted SPPA values;   forecasting forecasted MSE values based upon the on-bottom MSE values, wherein each of the forecasted MSE values occurs at a same time as one of the on-bottom MSE values; and   identifying the on-bottom MSE values that are lower than their corresponding forecasted MSE values, which represent second negative anomalies that indicate second drilling breaks, wherein the first portion of the subsurface interval and the second portion of the subsurface interval are also identified based upon the on-bottom MSE values that are lower than their corresponding forecasted MSE values.   
     
     
         19 . The non-transitory computer-readable medium of  claim 16 , wherein the operations further comprise:
 identifying a first portion of the subsurface interval based upon the first changepoints and the second changepoints, wherein the first portion of the subsurface interval corresponds to a first portion of rock with mechanical properties below a predetermined mechanical property threshold;   identifying a second portion of the subsurface interval based upon the first changepoints and the second changepoints, wherein the second portion of the subsurface interval corresponds to a second portion of rock that is conductive to a drilling fluid;   determining the cause of a lost circulation event in the subsurface interval based upon the first and second portions of the subsurface interval; and   determining whether the lost circulation event is curable.   
     
     
         20 . The non-transitory computer-readable medium of  claim 19 , wherein the operations further comprise performing a wellsite action in response to determining that the cause is curable, wherein the wellsite action comprises generating and transmitting a signal that instructs or causes a physical action to occur, and wherein the physical action comprises a lost circulation mitigation action in the wellbore.