Methods for downhole sampling of tight formations
There is provided a method of sampling a subterranean formation. The method includes the steps of creating a side bore into the wall of a well traversing the formation, sealing the wall around the side bore to provide a pressure seal between the side bore and the well, pressurizing the side bore beyond a pressure inducing formation fracture while maintaining the seal, pumping a fracturing fluid adapted to prevent a complete closure of the fracture through the side bore into the fracture, and reversing the pumping to sample formation fluid through the fracture and the side bore.
1. A method of sampling a subterranean formation, comprising the steps of
suspending a tool with side bore drilling, fluid storage and pumping capability from the surface to a desired location in a well;
creating a side bore into the wall of a well traversing said formation;
sealing said wall around the side bore to provide a pressure seal between said side bore and said well;
pressurizing the side bore beyond a pressure inducing formation fracture while maintaining said seal;
pumping a fracturing fluid adapted to prevent a complete closure of said fracture from a reservoir inside said tool through said side bore into said fracture; and
reversing the pumping to sample formation fluid through said fracture and said side bore.
2. A method in accordance with claim 1 , wherein the side bore is drilled in direction of the maximum horizontal stress.
3. A method in accordance with claim 1 , wherein the formation is uncased at the location of the side bore.
4. A method in accordance with claim 1 , wherein the formation is a low permeability formation.
5. A method in accordance with claim 1 , wherein the formation is a low permeability formation with a permeability below 100 mD.
6. A method in accordance with claim 1 , wherein the formation is a low permeability formation with a permeability below 20 mD.
7. A method in accordance with claim 1 , wherein the formation is a gas bearing shale formation of low permeability formation or tight gas formation.
8. A method in accordance with claim 1 , wherein the volume of fracturing fluid is less than 100 liters.
9. A method in accordance with claim 1 , wherein the volume of fracturing fluid is less than 20 liters.
10. A method in accordance with claim 1 , wherein fracturing fluid comprises a proppant.
11. A method in accordance with claim 10 , wherein fracturing fluid has a density sufficient to keep the proppant buoyant for the time required to position the tool fracture and inject the fracturing fluid.
12. A method in accordance with claim 1 , wherein fracturing fluid comprises a corrosive component for etching exposed surface of the fracture.