SIMULATION OF HYDRAULIC FRACTURING OF JOINTED ROCK

摘要

This paper presents a modeling approach for three-dimensional simulation of hydraulic fracturing of jointed rock. The base for a successful computer based simulation for productive use is the ability to calculate the fractured volume with sufficient accuracy and efficiency. Especially in cases three dimensional effects have to be taken into account, the common commercial software tools in oil and gas business reaches their bounds. There is a need for an effective modeling and simulation software tool to run three dimensional problems effectively. Effective 3D hydraulic fracturing simulation does not only mean that one hydraulic fracturing process can be modeled and simulated. To optimize the hydraulic fracturing design we need a parametric model and the simulation of one design has to be highly effective because during calibration and optimization the calculation of a couple of hundred different designs becomes necessary. Therefore the balance between accuracy and efficiency is the challenge to use computer based simulation of hydraulic fracturing for productive use. Dynardo developed a 3D-hydraulic fracturing simulator and coupled the simulator with leading edge calibration and optimization algorithms to offers the software base to optimize gas production with computer simulation. With the integrated approach, an effective 3D numerical reservoir simulator is available. The input parameters of the numerical model from the best available well log and reservoir data must be calibrated from the direct diagnostics measurements to assign the correct level of importance to various mechanisms of the hydraulic fracturing. Only with this degree of diagnostic characterization of the hydraulic fracture it is possible to truly understand the controls on the evolution of the fracture network geometry of hydraulic fractures. With this approach, a predictive model for the design of hydraulic fracture can be developed for a reservoir. By use of the predictive, calibrated model, the hydraulic fracturing design can be optimized to provide the required conductivity the hydraulic fracture design to maximize the gas production. For three dimensional modeling, analysis and post processing FEM simulator ANSYS® is used. The second key component is the material library of jointed rock multiPlas, which simulates the fracturing process. The third key component is the optimization tool op-tiSLang, which is used for calibration of the reservoir simulator and finally used for optimization of gas production. The simulator was set up and verified in Barnett Shale production area. The reservoir model was characterized with 7 rock layers and up to 4 sets of joints per rock layer. With the help of optiSLang a sensitivity study of the 200 physical and fracturing design parameters was performed to identify and calibrate the important physical parameters. The calibrated mode is then used to predict and optimize the gas production rates.