The Role of Formation Damage in Hydraulic Fracturing Shale Gas Wells

Abstract

Producing natural gas from shale gas presents a unique challenge to the petroleum engineers because of the low permeability nature of this type of gas reservoirs. Large scale hydraulic fracturing operations are often required for enhancing gas well productivity. Due to the shally characteristics of the reservoir rock, the productivity of the hydraulically fractured gas wells is very vulnerable to the damage by the fracturing fluids. The damaging mechanisms have been recognized to include fluid invasion, proppant embedment, gel filter cake at the fracture face, and the gel residue in the proppant pack. The relative significances of the well damage due to different mechanisms are not clear. It is highly desirable to have an analytical method for predicting the relative importance of different types of damage and optimizing fracturing treatment accordingly. This paper presents such a model and observations from model analyses.A new mathematical model was developed in this study to predict the effects of fracture fluid filtration, proppant embedment, gel filter cake at the fracture face, and the gel residue in the proppant pack on the productivity of fractured gas wells in shale gas reservoirs. A unique feature of the new model is that it considers reservoir-fracture cross-flow in wells with long fractures and non-linear influx to wells with short fractures. Sensitivity analyses with the model show that, among the investigated four mechanisms, the fluid invasion should have the most detrimental effect, while the formation of proppant-embedment layer should have a negligible effect on the productivity of fractured wells in shale gas reservoirs.

Review of Developments in Nanotechnology Application for Formation Damage Control

“…Production of oil and gas from tight and shale formation always needs a stimulation technique to create the complex network of artificial hydraulic fractures. A large volume of proppants is pumped into the formation to enhance transportation of shale gas from the formation to the wellbore in commercial quantities. − Such production requires the complex network of artificial fractures to have sufficient conductivity to sustain the whole period of production . Unfortunately, the techniques for transporting and placing proppants in the formation to hold the fractures exhibit formation damage near the fracture surface that affects fracture packing. − Many mechanisms impair the fracture conductivity during the process of fracturing. ,, These include proppant embedment, closure stress effect, , proppant crushing, , cyclic stress, fine migration, proppant pack diagenesis, , and the blockage caused by the gel residue in the proppant pack and gel filter cake at the fracture face. , …”

Analyses of Processes, Mechanisms, and Preventive Measures of Shale-Gas Reservoir Fluid, Completion, and Formation Damage

“…The trends in production after hydraulic fracturing is strongly influenced by decrease of fracture conductivity and reservoir formation permeability by damage caused during fracturing and post-fracturing production impairment is influenced by various potential damage mechanisms involved in stimulation of unconventional-gas-wells (Shaoul et al 2011, Guo et al 2011, Bahrami et al 2012, and Li et al 2012. Jackson and Rai (2012) describe the sources of skin effects involved in hydraulically-fractured shale gas wells completion efficiency caused by various completion resistances.…”

“…Mechanical damage from the hydraulic fracturing completion damage occurs by proppantembedment layer thickness formed by proppant penetration into reservoir formation matrix as a result of increase of closure stress during production after hydraulic fracturing ( Fig. 1) depending on the proppant size distribution, concentration, and reservoir formation type and surface of hydraulically-created fracture (Guo et al 2011 andLi et al 2012). Bennion (2002) and Reiniche et al (2013) explain that the stress-induced mechanical interactions between the proppant and reservoir formation fracture surface can cause proppant embedment into the near-fracture-face formation matrix, formation grains deformation, proppant and formation grains crushing, disintegration, and fine particles generation, and subsequent pore plugging in the compacted near-fracture face formation, the near-fracture face reduced permeability region can capture the fine particles internally during production.…”