A Practical Hydraulic Fracturing Model Simulating Necessary Fracture Geometry, Fluid Flow and Leakoff, and Proppant Transport

Abstract

ABSTRACT Hydraulic fracturing model using various sets of fracture flow/geometry equations are available in the industry. The majority of these models assume a constant fracture height selected at the start of the design, and simulate two-dimensional fracture geometry (width and length) and one dimensional fluid flow in both the fracture and the formation. The two-dimensional fracture geometry simulation can lead to optimistic estimates of fracture lengths and the one-dimensional flow may not allow adequate representation of proppant transport and fluid loss. Highly sophisticated hydraulic fracturing models are available that simulate three-dimensional fracture height and two-dimensional fluid flow throughout the entire fracture process. These models are versatile and are recommended for highly complex, layered reservoirs where rock material properties, in-situ stress distribution, and flow properties are variable at the wellbore and also throughout the reservoir. For everyday use by the completion/production engineer, hydraulic fracturing models need to be generated that are more advanced than the "conventional" two-dimensional models but simpler in approach and less costlier than the fully three dimensional models. The hydraulic fracturing model presented in this paper can be classified as a pseudo three-dimensional fracture geometry accounting for simple two-dimensional fluid flow. Fracture height at the wellbore, width, and length are computed simultaneously. These calculated parameters are then compensated for two-dimensional fluid flow which accounts for friction pressure drop and gravity. An iteration process is set-up until a satisfactory convergence is attained. Knowledge of appropriate fracture geometry and two-dimensional fluid flow enhances the accuracy in fluid loss calculations and proppant transport. Special data required as input to this model include the in-situ stress and mechanical properties distribution in and around the pay zone. The paper presents hydraulic fracturing theory and the basis of the model under discussion. A detailed explanation of the model is also presented where field examples are used to illustrate its use and importance.