Method of Forming Directionally Controlled Wormholes In A Subterranean Formation

Abstract

A method for forming extended wormholes in a subsurface formation comprising locating producer wells, injection wells, and guard wells in a field; determining a flux rate for a formation-dissolving fluid such as an acid, the flux rate being dependent upon different variables including the composition of the rock matrix making up the subsurface formation and the type of acid selected; injecting a guard fluid into the subsurface formation, through at least one guard well to form designed pressure boundaries and injecting the acid into the formation at a rate to reach the determined flux rate and thereby forming an extended network of wormholes through the subsurface formation in a defined direction or plane, with or without guard wells.

What is claimed is: 
     
         1 . A method of modeling a subterranean formation, the formation having a low permeability region, and the method comprising:
 determining a lithology of a rock matrix in the subterranean formation;   determining a flux rate for a selected formation-dissolving fluid in the rock matrix;   inputting a formation parting pressure of the subterranean formation;   locating a proposed injection well in a software-based 3D model representing the subterranean formation;   locating a proposed producer well in the 3D model for the subterranean formation juxtaposed from the injection well;   locating a pair of fluid barriers in the 3D model for the subterranean formation, such that the fluid barriers are on opposing sides of the injection well, with at least one of the fluid barriers being a guard well;   running the 3D model to confirm the formation of wormholes along a plane extending between the injection well and the producer well when:
 (i) a guard fluid is injected through the at least one guard well and into the subterranean formation, thereby creating pressure boundaries; and 
 (ii) the formation-dissolving fluid is injected through the injection well and into the subterranean formation at an injection pressure that is less than a parting pressure of the rock matrix. 
   
     
     
         2 . The method of  claim 1 , wherein the wormholes comprise a network of wormholes extending substantially along the plane for a length of at least 11 feet. 
     
     
         3 . The method of  claim 1 , wherein:
 the rock matrix comprises primarily a carbonate material; and   the formation-dissolving fluid is an acid.   
     
     
         4 . The method of  claim 3 , wherein the acid comprises a hydrochloric acid in an emulsion. 
     
     
         5 . The method of  claim 2 , wherein the production well, the injection well and the at least one guard well are each situated horizontally and in the same general azimuth within the subterranean formation. 
     
     
         6 . The method of  claim 2 , wherein the pair of fluid barriers comprises (i) a pair of guard wells that receive the guard fluid; or (ii) a guard well and an impermeable layer. 
     
     
         7 . The method of  claim 6 , further comprising:
 adjusting the location of the pair of fluid barriers; and   running the 3D model again in order to change a planar orientation of propagation of wormholes in the rock matrix.   
     
     
         8 . The method of  claim 2 , further comprising:
 changing a temperature of the acid, the composition of the acid, or both;   determining a new flux rate for the acid in the rock matrix; and   running the 3D model again in order to determine a length of the propagation of wormholes in the rock matrix.   
     
     
         9 . The method of  claim 2 , wherein determining a lithology of the rock matrix comprises (i) determining a temperature of the subsurface formation, (ii) determining a permeability of the subsurface formation, (iii) determining a porosity of the subsurface formation, (iv) determining in situ pressures within the subsurface formation, or (v) combinations thereof. 
     
     
         10 . The method of  claim 9 , wherein the plane of propagation of the wormholes extends parallel to a direction of least minimum principal stress in the rock matrix or perpendicular to a direction of least minimum principal stress in the rock matrix. 
     
     
         11 . The method of  claim 9 , wherein the plane of propagation of the wormholes extends in a direction that is neither parallel to nor perpendicular to a direction of least minimum principal stress in the rock matrix.