Fracture Characterization Using Directional Electromagnetic Resistivity Measurements

Abstract

A disclosed fracture characterization method includes: collecting three-dimensional resistivity measurements of a volume surrounding an open borehole; analyzing the measurements to determine parameters describing fractures in the volume; and providing a report to a user based at least in part on said parameters. A fluid with a contrasting resistivity is employed to make the fractures detectable by a directional electromagnetic logging tool in the borehole. illustrative parameters include fracture direction, height, extent, length, and thickness. The resistivity measurements can be augmented using a borehole wall image logging tool. Also disclosed are fracturing methods that include: positioning a directional electromagnetic logging tool proximate to a formation; fracturing the formation; monitoring fracture progression with said tool; and halting the fracturing when measurements by said tool indicate that a predetermined set of criteria have been satisfied.

1 . A fracture characterization method that comprises:
 collecting three-dimensional measurements of a volume surrounding an open borehole, wherein the volume includes at least one fracture filled with a fluid having a resistivity that contrasts with the formation;   analyzing the measurements to determine at least one parameter describing said fracture; and   providing a report to a user based at least in part on said parameter.   
     
     
         2 . The method of  claim 1 , wherein the at least one parameter comprises a fracture direction. 
     
     
         3 . The method of  claim 1 , wherein the at least one parameter comprises at least one dimension in the set consisting of a fracture height, a fracture extent, a fracture length, and a fracture thickness. 
     
     
         4 . The method of  claim 1 , further comprising injecting said fluid into the borehole before collecting said measurements. 
     
     
         5 . The method of  claim 1 , further comprising collecting a borehole wall image log to measure characteristics of said fracture where it intersects the borehole. 
     
     
         6 . The method of  claim 6 , wherein the three-dimensional measurements are acquired by a directional electromagnetic resistivity tool, and the borehole wall image log is acquired by an acoustic tool or a micro-resistivity tool. 
     
     
         7 . A logging assembly that comprises:
 an electromagnetic resistivity tool that acquires resistivity measurements as a function of position, orientation, and radial distance;   a borehole wall image logging tool that acquires borehole wall measurements as a function of position and orientation; and   an uphole or downhole processor that combines said resistivity and borehole wall measurements to detect fractures and create a log of at least one fracture parameter.   
     
     
         8 . The logging assembly of  claim 7 , wherein the at least one fracture parameter includes a parameter from the set comprising fracture direction, fracture height, fracture extent, fracture length, and fracture thickness. 
     
     
         9 . The logging assembly of  claim 7 , further comprising a processing system that displays said log to a user. 
     
     
         10 . A fracturing method that comprises:
 positioning a directional electromagnetic logging tool proximate to a formation;   fracturing the formation;   monitoring fracture progression with said tool; and   halting the fracturing when measurements by said tool indicate that a predetermined set of criteria have been satisfied.   
     
     
         11 . The method of  claim 10 , wherein said monitoring includes:
 collecting three-dimensional measurements of the formation with said tool while fracturing;   deriving at least one fracture dimension from said measurements; and   determining whether the at least one fracture dimension satisfies the set of criteria.   
     
     
         12 . The method of  claim 10 , wherein the set of criteria includes a minimum length subject to a maximum extent. 
     
     
         13 . The method of  claim 10 , wherein said fracturing includes injecting a fracturing fluid having a resistivity less than 10% of the formation's resistivity. 
     
     
         14 . The method of  claim 10 , wherein said fracturing includes injecting a fracturing fluid having a conductivity less than 10% of the formation's conductivity. 
     
     
         15 . The method of  claim 10 , further comprising:
 obtaining a borehole wall image log; and   combining information from the borehole wall image log with said measurements to determine at least one fracture dimension.   
     
     
         16 . A fracturing assembly that comprises;
 a fluid injection port that supplies a fluid into a borehole in a formation;   a directional electromagnetic logging tool positioned to obtain three-dimensional measurements of the formation exposed to the fluid; and   a processor that determines fracturing progress from said measurements and communicates said progress to an operator.   
     
     
         17 . The fracturing assembly of  claim 16 , wherein the port jets the fluid against the borehole wall, and wherein the port is located between antennas of the directional electromagnetic logging tool. 
     
     
         18 . The fracturing assembly of  claim 16 , wherein the directional electromagnetic tool is a wireline tool suspended through the fluid injection port. 
     
     
         19 . The fracturing assembly of  claim 16 , further comprising a borehole wall imaging tool. 
     
     
         20 . The fracturing assembly of  claim 16 , wherein the processor extracts at least one fracture dimension from said measurements, wherein the at least one fracture dimension is in a set consisting of fracture direction, fracture height, fracture extent, fracture length, and fracture thickness.