Functional Relationship between Amount of Diverting Agent and Diverting Angle in Fracturing Tight Sandstones in Sulige Gas Field

Field practices have proved that fuzzy ball diverting agent is able to control fracture strike by altering rock strengths, theoretical study on diversion of fractures is rarely seen though. The relationship between the strength of diverting agent and diverting angle is one the key factors that ensures the diverted fractures extend to the designed positions. Diverting agent plugging experiment and rock triaxial stress experiment were done on a fuzzy ball diverting agent formulation:2.0% epithecium agent+1.5% fuzz agent + 0.3% nucleating agent+0.5% filming agent. When injecting 4, 8, 10 and 12 mL fuzzy ball diverting agent, the pressure bearing capacity of the formation being plugged by the diverting agent was 10.15 MPa,12.37 MPa,16.52 MPa and 25.14 MPa, respectively. An artificial sandstone core of 75 mm in diameter was tested on triaxial stress tester before and after being plugged with the fuzzy ball diverting agent, an inflexion point was found on the radial stress-strain curve at which the strain increased from 0.0048 mm/mm to 0.0127 mm/mm. On axial stress-strain curve there was also an inflexion point at which the strain increased from 0.0143 mm/mm to 0.0186 mm/mm. These data indicate that rock strength was increased. In calculating elastic modulus by dividing stress by axial strain, and Poisson ratio by dividing transversal strain by axial strain, in was found that the incremental diverting angles measured were 24.9°, 23.2°, 37.5°, and 55.9°, respectively. Four rocks after being plugged had elastic modulus of 19.55 GPa, 16.65 GPa, 19.61 GPa and 19.77 GPa, respectively, and Poisson ratios of 0.36, 0.30, 0.46 and 0.38, respectively. Using elastic modulus and Poisson ratio as the parameters affecting diverting angle, fit the mathematical relationship between the parameters and the diverting angle of fractures with least square method. It was found that the natural logarithm of the quotient of elastic modulus/Poisson ratio was linearly related to the diverting angle. From this finding a functional relationship between injection amount of diverting agent with diverting agent has been worked out. It is understood that the injection amount of the fuzzy ball fracturing fluid is able to control the diverting angle, thereby extending the diverted fractures to the target zones.