Integrated Data Analysis Reveals the Presence of Sealed Fractures in a Large Tight Gas Field

Abstract

Abstract One of the largest gas fields in the Sultanate of Oman was developed between 2010 and 2016 by drilling 26 vertical wells for commingled production from three deep tight gas sandstone stacked reservoirs. The shallower reservoir is a rich gas condensate reservoir, while the other two contain lean gas fluids. Over the last few years, the wells performance has been poorer than anticipated. An integrated study was carried out in 2016-2017 to identify the root causes of this under performance and eventually address it in a new field development plan. All subsurface and surface disciplines worked together analyzing available data in order to understand the production behaviour and complex nature of the field. One of the major findings of the integrated study was the interpreted presence of sub-seismic lineaments corresponding to possible zones of quartz sealed fractures. This was supported by seismic, core, reservoir pressure (MDT) and pressure build up data. The integrated data analysis revealed that these lineaments are having a direct impact on the field performance, as the hydrocarbon in-place volume seen by each well is dependent on the compartments defined by these lineament boundaries. A large set of lineaments were added to the dynamic model after mapping from detailed seismic work. This addition resulted in very good matches of historical production and pressure data. These updates to the reservoir model will ensure a more accurate field forecast and provide a better field development strategy. This paper will demonstrate that the presence of sealed sub-seismic fractures that may remain undetected can have a substantial impact on the performance of tight gas reservoirs. By identifying these sub-seismic elements and understanding their impact through an integrated approach, field performance can be better forecasted in order to account for the presence of these features.