Optimization Strategies for Hydraulic Fractures in High Permeability Reservoirs

Abstract

Abstract High permeability fracturing, commonly referred to as a frac&pack treatment, is becoming an increasingly popular completion option for both well productivity improvement and sand control in poorly consolidated formations. This paper presents an efficient and effective economic optimization scheme for hydraulic fractures in high permeability formations. The optimization scheme incorporates global optimization algorithms that simultaneously optimize all of the treatment parameters, including fracture dimensions, while accounting for the required constraints. The scheme is not dependent on specific fracture geometry or production prediction models, and the optimization algorithms are more efficient than the approaches currently used. Parametric studies were conducted, and some general trends and guidelines were observed. Field data from frac&pack treatments were reviewed and compared to the findings of this research. A review of field data indicates that the results of our optimization scheme are realistic, confirming some of the conclusions derived from the parametric studies and suggesting that this approach can be a useful tool for designing fracture treatments in high permeability reservoirs. Introduction Traditionally, hydraulic fracturing has been used predominantly for the stimulation of low permeability reservoirs. The excessive fluid leakoff expected with high permeability formations and difficulties arising from the unconsolidated sands often associated with these reservoirs were thought to preclude the successful implementation of a hydraulic fracture with sufficient conductivity to be economically viable. In recent years, techniques for successfully fracturing high-permeability and poorly consolidated reservoirs have been developed and improved, leading to an increasingly popular method for the stimulation and control of sand production in these reservoirs. The key technique that enabled the use of hydraulic fractures in high permeability reservoirs is a tip screenout (TSO). This involves arresting the lateral propagation of the created fracture; subsequent inflation and packing of the fracture provides the required width/conductivity. The treatment may thus be split into two parts:the TSO stage, andthe fracture inflation and packing (FIP) stage. The resulting fracture is much shorter and much wider than a traditional low-permeability hydraulic fracture. This two-in-one combination treatment is often called a frac&pack treatment. Similar to conventional (low permeability) fracturing, frac&pack treatments bypass near-wellbore damage, providing effective stimulation when acidizing may not be successful. By reducing the pressure drawdown and fluid flux in the reservoir, these treatments also provide effective sand control. In addition to this indirect sand control via reduction in near-wellbore pressure gradients and flow velocities, frac&packs also help control sand production in a more direct manner. This is achieved by increasing effective stresses acting on the formation, in effect compacting and stabilizing the sandface, as well as by exerting a physical filtering effect similar to conventional gravel packs. Frac&pack treatments have been shown to provide superior sand control without the loss in productivity associated with conventional sand control methods. In addition to the initial increased productivity compared to gravel packs, frac&pack treatments often experience an improvement in productivity with time whereas conventional gravel pack completions deteriorate with time. In fact, this technique has recently gained wide acceptance as an effective sand control method and several companies currently employ frac&pack treatments as the preferred completion method in certain sand-producing regions.1,2,3,4