Reducing Exploration and Appraisal Risk in Low-Permeability Reservoirs Using Microseismic Fracture Mapping

Abstract

Low-permeability reservoirs have been actively developed and considered economically viable for more than 30 years in North America, but their development has been limited elsewhere. In North America, significant infrastructure is already in place and drilling and completion costs are relatively low. The typical exploration and appraisal approach is to drill a relatively large number of low cost wells to assess economic viability. Outside North America, however, infrastructure is less developed, and costs are often higher. To achieve economical development in these areas, operators must assess resource viability by drilling as few wells as possible. The many-wells model has made international operators reluctant to explore low-permeability reservoirs in some areas. However, there is increasing interest in developing the vast resources held in tight gas, coalbed methane, and gas shale plays outside North America.The exploration and appraisal of low-permeability reservoirs or unconventional plays is significantly different than conventional reservoirs; exploration is more like appraisal, requiring pilot programs to test commerciality of these resource plays prior to embarking upon large-scale development (Hall 2007;Stabell 2007), including the effect of completion and stimulation optimization (Haskett and Brown 2005). One essential component of low-permeability reservoir development is hydraulic fracturing, which virtually all of these wells require. With the introduction of hydraulic fracture monitoring (HFM), we are now able to measure fracture geometry and complexity, which has led to major improvements in treatment designs, well completions, and field development strategies in North America. HFM applications were once focused on development and infill drilling, but they have recently shown significant value for exploration plays (primarily in gas shale). HFM measurements now allow operators to more efficiently evaluate the effectiveness of stimulation treatments and completion approaches in exploration and appraisal wells, reducing the number of wells required to assess the economic viability of low-permeability reservoirs.The application of HFM to exploration and appraisal programs outside North America could significantly accelerate the evaluation of low-permeability reservoirs, where selecting the appropriate hydraulic fracturing design and well completion strategy will be key to success. It could also accelerate the learning curve, which is essential to quickly reducing costs.

Enhanced natural gas recovery from low-permeable reservoirs

“…As it was established by the results of field research works and gained field experience of gas production from unconventional deposits, some amount of gas is in adsorbed state [11][12][13]. One of the possible and main ways of gas production increase from low-porous low-permeable reservoirs is gas desorption stimulation from the surface of the pore channels.…”

Modeling and Control of Proppant Distribution of Multistage Hydraulic Fracturing in Horizontal Shale Wells

“…3,4 Although multistage hydraulic fracturing has resulted in tremendous cost savings by generating simultaneously growing multiple fractures, because of the uneven proppant distribution only 30−40% of the perforation clusters participate in gas and oil production. 5,6 "Stressshadowing" phenomenon is one of the important contributing factors for the uneven proppant distribution. 7−9 Stress shadow effects refer to additional stresses exerted by an opening fracture on the surrounding rock formation and adjacent fractures.…”

“…Typically, the spacing between fractures in simultaneously growing multiple fractures is between 10 to 30 m, and the closely spaced fractures often distribute the fracturing fluid unevenly between the fractures resulting in nonuniform fracture geometry. , Although multistage hydraulic fracturing has resulted in tremendous cost savings by generating simultaneously growing multiple fractures, because of the uneven proppant distribution only 30–40% of the perforation clusters participate in gas and oil production. , “Stress-shadowing” phenomenon is one of the important contributing factors for the uneven proppant distribution. − Stress shadow effects refer to additional stresses exerted by an opening fracture on the surrounding rock formation and adjacent fractures. For simultaneously growing multiple fractures, fracturing fluids are distributed into multiple fractures based on pressure drops because of perforation friction, wellbore friction, and fracture propagation.…”

Fracture Network Connectivity — A Key To Hydraulic Fracturing Effectiveness and Microseismicity Generation

“…The extremely low permeability of the common shale plays means that simple, bi-planar hydraulic fractures (HF) do not create enough surface area to make economic wells and that stimulation of the natural fracture system is critical [1]. Numerous field microseismic data sets have shown that extreme fracture complexity may result from the interaction between a created hydraulic fracture and the pre-existing fracture network [2,3]. Consequently, operators will often alter the stimulation design, by changing injection rate, viscosity, or other parameters, in order to improve the effectiveness of the stimulation in unconventional shale plays.…”