Application And Methods Research Of Fracture Pressure Prediction With Logging Data

The fracturing pressure of formation is the base of designing drilling, choosing drilling fluid, and deciding the depth of casing.The fracturing pressure is relative to rock’s original strength, pore pressure and earth stress. In this paper, the relation between rock’s stress and strain is analyzed. The elastic modulus can be calculated with logging data. According to empirical formula and rock’s fracture criterion, the rock’s original strength can be computed. The principle and method of predicting pore pressure with logging data is studied. And the result indicates that the full wavetrain acoustic logging data is more effective. Considering tectonic stress’ s effect, the generalized tectonic stress gene is introduced. Through analyzing the stress field around the borehole and fracture mechanism, the fracturing pressure of formation can be calculated. It includes tension fracture, shear fracture and burst fracture. Tension fracture includes natural fracture and compressive fracture. Natural fracturing pressure is the pressure when mud lost. Cavingin fracturing pressure is the bigger between shear and burst fracturing pressure.During the course of drilling, shear damage will happen around the borehole when the drilling fluid pressure is less than the cavingin fracturing pressure. At this point, plastic flow will happen in plastic rock, which conduces to borehole reduction. And collapse will happen in brittle rock, which conduces to borehole enlargement. When the natural fracturing pressure is less than the drilling fluid pressure, tensile rupture will happen around the borehole, which leads to mud loss. The maximum, minimum, and optimal mud weight can be computed with the fracturing pressure data. So good reference is provided for choosing reasonable drilling fluid density and such accident as blowout and mud loss can be prevented.In the course of exploratory development, in order to obtain industrial oil stream, hydraulic fracturing should be adopted in low porosity and permeability reservoirs. The stress intensity factor of fracture propagation and rock’s tenacity can be calculated with logging data, then the fracture height can be computed. This can provide reasonable pump pressure increment and reference value for frac construction.The methods to predict fracturing pressure and evaluate cementing quality have been applied in actual data and the results have been validated with local data. The predicting fracturing pressure is correct and the error can be controlled in small range when the logging data is enough.