Production performance of hydraulic fractures in tight gas sands, a numerical simulation approach. Journal of Petroleum Science and Engineering

Hydraulically fractured tight gas reservoirs are one of the most common unconventional gas sources being produced today, and will be a regular source of gas in the future. The extremely low permeability of tight gas sands leads to inaccuracy of conventional build-up and draw-down well test results. This is primarily due to the increased time required for transient flow in tight gas sands to reach pseudo-steady state condition. To increase accuracy, well tests for tight gas reservoirs must be run for longer periods of time which is in most cases not economically viable. The large amount of downtime required to conduct well tests in tight sands makes them far less economical than conventional reservoirs, which leads to the need for accurate simulation of tight gas reservoir well tests. This paper presents simulation results of a 3-D hydraulically fractured tight gas model created using Eclipse software. The key aims are to analyze the effect of differing fracture orientation, number and length. The focus of the simulation runs will be on the effect of hydraulic fracture orientation and length. The results will be compared to simulation runs without the abovementioned factors to determine their effects on production rates and well performance analysis. All results are plotted alongside an un-fractured tight gas scenario in order to put the hydraulic fracture performance in perspective. Key findings from this work include an approximately linear relationship between initial gas rate and the number of hydraulic fractures intersecting the wellbore. In addition, fracture length is found to have less of an impact on initial gas rate compared to number of fractures intersecting the wellbore, for comparable total fracture volumes

Hydraulic fracture productivity performance in tight gas sands, a numerical simulation approach

Hydraulically fractured tight gas reservoirs are one of the most common unconventional sources being produced today, and look to be a regular source of gas in the future. Tight gas sands by definition have extremely low permeability and porosity, and are most often uneconomical to produce without the aid of some form of reservoir stimulation. Hydraulic fracturing is one of the most common forms of commercially extracting gas from tight gas sands and is becoming increasingly popular in America, Canada and the rest of the world, with some projects in Australia.Along with the low productivity, tight gas sands are faced with other additional challenges if compared to conventional reservoirs, such as near wellbore damage due to water blocking, mechanical damage, fluid invasion and wellbore breakouts. In addition, inaccuracy of conventional build-up and draw-down well test results is common. This is primarily due to the increased time required for transient flow in tight gas sands to reach pseudo-steady state condition. To increase accuracy, well tests for tight gas reservoirs must be run for longer periods of time which is in most cases not economically viable. This leads to the need for accurate simulation of tight gas reservoir well tests or a reduction in analysis time.The primary aim of this research project is to use early time well test and production data to determine insights into hydraulic fracture productivity performance. The work is presented with reference to two published peer-reviewed papers published as lead author and one peer-reviewed paper published as co-author. The two main methods of analysis used will be Horner plot and a semi-log plot of production rate vs. log-time. Sensitivity analysis on fracture number, size and orientation with respect to the wellbore are conducted.The production and pressure buildup data is generated using commercial 3-D reservoir simulation software, Eclipse. A box model with generic tight gas properties is created with realistic hydraulic fracture and well completion simulated. Data is either compared to an unfractured tight gas sand model, or to a model with different number of fractures but comparable overall fracture volume

Evaluation of Damage Mechanisms and Skin Factor in Tight Gas Reservoirs

Tight gas reservoirs normally have production problems due to very low matrix permeability and significant damage during well drilling, completion, stimulation and production. Therefore, they may not flow gas at optimum rates without advanced production improvement techniques. The main damage mechanisms and the factors that have significant influence on total skin factor in tight gas reservoirs include mechanical damage to formation rock, plugging of natural fractures by mud solid particles invasion, relative permeability reduction around wellbore as a result of filtrate invasion, liquid leak-off into the formation during fracturing operations, water blocking, skin due to wellbore breakouts, and the damage associated with perforation. Drilling and fracturing fluids invasion mostly occurs through natural fractures and may also lead to serious permeability reduction in the rock matrix that surrounds the natural or hydraulic fractures.This study represents evaluation of different damage mechanisms in tight gas formations, and examines the factors that can have significant influence on total skin factor and well productivity. Reservoir simulation was carried out based on a typical West Australian tight gas reservoir in order to understand how well productivity is affected by each of the damage mechanisms such as natural fractures plugging, mud filtrate invasion, water blocking and perforation