How to Maximize the Value of the Lajas Tight Gas Play by Dynamic Modeling

Abstract

The Lajas formation in the Neuquén Basin, Argentina, has been identified as a key opportunity to supply the gas requirements of the Argentine economy. A number of fields are currently being developed in this formation with an ongoing exploration program likely to yield more discoveries. Maximizing the value of existing and new assets was the task at hand. To optimize the development, dynamic models were needed to produce forecasts for different development scenarios. One of the main issues to solve was how to represent in commercial dynamic software the hydraulic fractures and their interaction with a low permeability formation. The optimum approach to model induced fractures had to be identified. Additionally, flow tests of wells were infrequent and often gave contradictory results. Hence we explored a number of different options for controlling the history match and forecast such as controlling by gas rate, tubing head pressure and back pressure through the choke. We concluded that dual porosity modeling of the fractures offered an acceptable balance between computational overhead, absolute accuracy and flexibility. The main parameters adjusted to achieve the history match were the fractures half length, height, volume and conductivity/permeability that ruled the early behavior of the wells and the matrix permeability that conditioned their longer term productivity. Controlling the wells in the history match was found to be best achieved by control through the choke and line pressure. Tubing head pressure as well as gas and water simulated rates were cross checked against historical data. The vertical lift performance modeling of the wells was also found to be critical to achieve the history match. The pressure drop in the wells was modelled by lift curves from the well head to the first perforation and by segments from there onwards to understand their liquid loading. All this had to be taken into account due to the fact that wells were impacted by tubing, choke and line pressure changes through their production history. It was possible to optimize Lajas gas development by applying an integrated modelling methodology linking geology, reservoir and production engineering. The model helped justify new infill locations and estimate the difference in productivity between different Lajas geological sequences. The dynamic model results were compared with the outcome of other forecasting methods such as DCA Tipe Well, RTA and layercake dynamic models.