Methods, strings and tools to enhance wellbore fracturing

Abstract

A tubing string external structure forms a pathway in a cemented annulus that extends from a fluid treatment port axially away from the port and along a length of the tubing string. Wellbore treatment fluids can be injected through the tubing string and through the pathway to contact the wellbore wall along a length greater than the axial length of the port.

I claim: 
     
         1 . A wellbore tubular comprising:
 a wall having a first end, an opposite end, an inner surface and an outer surface;   a port extending through the wall, the port including an upper end wall and a lower end wall, the distance between the upper end wall and the lower end wall defining the open axial length of the port; and   an external structure carried on the outer surface, the external structure overlying at least a portion of the axial length and extending axially from the port beyond at least one of the upper end wall and the lower end wall, the external structure operable to create a pathway through hardened cement in position about the outer surface for passage of fracturing fluid from the port axially along the outer surface away from the port and toward the first end.   
     
     
         2 . The tubular of  claim 1  wherein the external structure includes one or more of a collection of fibers, a hollow member, foam, materials degradable in cemented wellbore conditions, and deformable materials to form a pathway through set cement surrounding the external structure. 
     
     
         3 . The tubular of  claim 1  wherein the external structure includes a filler that (i) prevents infiltration of a liquid cement into the external structure, (ii) forms voids in cement that enters the external structure (ii) prevents setting of cement that enters the cement diffuser. 
     
     
         4 . The tubular of  claim 1  wherein the port has an open condition wherein fluid can pass through the port from the inner surface to the outer surface and the external structure overlies the at least a portion of the axial length when the port is in the open condition. 
     
     
         5 . The tubular of  claim 1  wherein the external structure is a spiral structure wrapping helically about the outer surface. 
     
     
         6 . The tubular of  claim 1  wherein the external structure is a sleeve-type structure substantially surrounding the outer surface. 
     
     
         7 . A tubular installation in place in a borehole, the tubular installation creating an annular space between the tubular installation and a wall of the borehole, the tubular installation comprising: a tubular including a wall having an inner surface and an outer surface; a port extending through the wall, the port including an upper end wall and a lower end wall the distance between the upper end wall and the lower end wall defining the open axial length of the port and the port having an open condition wherein fluid can pass through the port from the inner surface to the outer surface; and an external structure carried on the outer surface, the external structure overlying at least a portion of the axial length of the port in the open condition and extending axially from the port beyond at least one of the upper end wall and the lower end wall. 
     
     
         8 . The tubular installation of  claim 7  further comprising cement in the annular space and wherein the external structure forms a pathway through the cement due to at least one of: (i) by substantially blocking clear access into the external structure by the cement; (ii) a chemical applied to block access of the cement into the external structure; (iii) any cement that enters the external structure is thin, porous or unstable that the cement in the external structure is relatively weak; (iv) degradation of the external structure from within the cement; and (v) deformation of the external structure within the cement. 
     
     
         9 . The tubular installation of  claim 7  wherein the external structure extends from the outer surface to a position close to the wall of the borehole. 
     
     
         10 . A method for fracturing a wellbore, the method comprising: injecting fluid through a tubing string and out through a port into a cemented annulus between the tubing string and a wellbore wall, the fluid following a pathway through the cemented annulus, the pathway extending longitudinally away from the port and outwardly from the port close to the wellbore wall; and contacting the wellbore wall with the fluid to create a fracture in the wellbore wall. 
     
     
         11 . The method of  claim 10  further comprising pumping cement to form the cemented annulus and wherein during pumping an area free of cement is formed by an external structure through which extends the pathway. 
     
     
         12 . The method of  claim 10  further comprising pumping cement to form the cemented annulus and wherein during pumping an area of weakened cement forms in an external structure through which extends the pathway. 
     
     
         13 . The method of  claim 10  wherein the pathway is formed by degradation of an external structure secured on an outer surface of the tubing string. 
     
     
         14 . The method of  claim 10  wherein the pathway is formed by deformation of an external structure secured on an outer surface of the tubing string. 
     
     
         15 . The method of  claim 10  wherein during injecting fluid through the port, an external structure secured to the tubing string provides the pathway for the injected fluids to pass through the cemented annulus. 
     
     
         16 . The method of  claim 10  wherein during injecting fluid through the port, an external structure secured to the tubing string is pushed aside. 
     
     
         17 . The method of  claim 10  wherein during injecting fluid through the port, an external structure secured to the tubing string is expelled to open the pathway. 
     
     
         18 . The method of  claim 10  wherein prior to or during injecting fluid through the port, an external structure secured to the tubing string is broken down to open the pathway. 
     
     
         19 . The method of  claim 10  wherein contacting the wellbore wall occurs at a position axially offset along the cemented annulus from the port. 
     
     
         20 . The method of  claim 10  wherein contacting the wellbore wall creates a fracture in an area containing naturally weak rock. 
     
     
         21 . The method of  claim 10  wherein contacting the wellbore wall creates both primary and secondary fractures. 
     
     
         22 . The method of  claim 10  wherein the tubing string includes an inner diameter, a bottom end and a tubular installed along the tubular string, the tubular including a wall with the port extending therethrough and a cement diffuser installed over the port and carried along with the tubular, the cement diffuser secured over the port on at least the outer diameter of the tubular overlying at least a portion of the port's axial length and extending axially from the port beyond at least one of its upper end wall and its lower end wall; pumping cement through the tubular string inner diameter, into an annular area about the tubing string and about the cement diffuser; allowing the cement to set in the annulus to provide the cemented annulus with the cement diffuser providing the pathway; and, injecting proceeds after allowing the cement to set. 
     
     
         23 . The method of  claim 22  wherein during pumping cement infiltrates voids in the cement diffuser and when allowing the cement to set, the cement in the voids sets. 
     
     
         24 . The method of  claim 22  wherein during pumping cement infiltrates voids in the cement diffuser and when allowing the cement to set, the cement in the voids is retarded from setting. 
     
     
         25 . The method of  claim 22  wherein during pumping cement fails to infiltrate voids in the cement diffuser. 
     
     
         26 . The method of  claim 22  wherein during pumping cement is deterred from infiltrating voids in the cement diffuser by the presence of a chemical in the cement diffuser. 
     
     
         27 . The method of  claim 22  wherein the pathway is a void formed by the cement diffuser in the cemented annulus and during injecting, the injected fluids pass through the void in the cemented annulus. 
     
     
         28 . The method of  claim 22  wherein the pathway is an unstable region formed by the cement diffuser in the cemented annulus and during injecting, the injected fluids pass through the unstable region in the cement annulus. 
     
     
         29 . The method of  claim 22  wherein during injecting, the cement diffuser is pushed aside. 
     
     
         30 . The method of  claim 22  wherein during injecting fluid through the port, the cement diffuser is expelled. 
     
     
         31 . The method of  claim 22  wherein during injecting fluid through the port, the cement diffuser is broken down. 
     
     
         32 . The method of  claim 22  wherein during pumping, cement is pumped through the bottom end of the tubular string into the annular area. 
     
     
         33 . The method of  claim 22  wherein the cement diffuser includes a plurality of fibers extending substantially radially out from the tubular, relative to a circular dimension of the tubular. 
     
     
         34 . The method of  claim 27  further comprising selecting the length of the plurality of fibers to touch the wellbore wall, when the tubular is installed in the wellbore.