Impact of Liquid Loading in Hydraulic Fractures on Well Productivity

Abstract

This article, written by JPT Technology Editor Chris Carpenter, contains highlights of paper SPE 163837, ’Impact of Liquid Loading in Hydraulic Fractures on Well Productivity,’ by Samarth Agrawal and Mukul M. Sharma, SPE, The University of Texas at Austin, prepared for the 2013 SPE Hydraulic Fracturing Technology Conference, The Woodlands, Texas, USA, 4-6 February. The paper has not been peer reviewed. One of the major challenges in fracturing low-permeability gas formations is the loss of well productivity caused by fluid entrapment in the matrix or fracture. Studies have suggested that this water is trapped in the rock matrix near the fracture face and remains trapped because of the high capillary pressure in the matrix. This study shows that, in regard to hydraulic fractures in horizontal wells, the fluid may also be trapped within the fracture itself and may affect the cleanup as well as productivity.  Introduction The loss of fracturing fluid and its impact on the productivity of hydraulically fractured wells have been studied for many years. Conventional wisdom suggests that the liquid is trapped at the fracture face because of capillary effects. This reduces the relative permeability of the hydrocarbon phase during flowback. Most studies published thus far on the subject ignored the accumulation of liquid in the fracture itself and the effect of gravity and fluid segregation in the fracture. In this study, we show that liquid accumulation in the fracture itself can be significant and that this fluid saturation is coupled with the fluid saturation in the matrix, leading to a very different cleanup profile and time scale for cleanup. A 3D reservoir simulator was used to investigate liquid loading in hydraulic fractures in a horizontal well. Generally, hydraulic fractures in horizontal wells range from tens to hundreds of feet in height. If liquid loading takes place in a certain section of the fracture, it will impair the flow of gas there. This will lead to a reduction in the effective producing fracture area, even if the drawdown is greater than the capillary pressure.  Liquid Loading Inside the Fracture. The desired lift velocity for unloading liquid and the available gas velocity in a fracture differ by almost two orders of magnitude. It is, therefore, very like-ly that the lower portions of fractures will be filled with liquid when production is initiated. This suggests that concerning load recovery from hydraulically fractured horizontal wells, even if the drawdown is able to overcome the capillary pressures, the inflow gas velocity may not be high enough to lift the liquid against gravity into the wellbore (Fig. 1). Liquid loaded inside the fracture in this way will affect the productivity of the well and the cleanup of the matrix. Understanding the conditions for liquid loading within the fracture will help identify remedial measures, which may be significantly different from remedial measures for reducing liquid blocking at the fracture face.