In 2009 PDO started an ambitious tight and deep gas exploration programme, exploring for previously untapped reservoirs, both conventional tight gas plays as well as deep unconventional gas resources. These resources are typically in previously undrilled formations at great depths, highly overpressurized with high temperatures, and uncertain fluid fill and composition. The unique geological properties of these reservoirs require different strategies to acquire the necessary data to enable the assessment of fluid compositions, permeability and well productivity data that are essential input to development decisions.
The acquisition of formation permeability and productivity data is very challenging in these environments; the paper will demonstrate how well-testing data has been used to gather information on fluid flow characteristics and dynamic properties where hydraulic fraccing is routinely used to achieve commercial production rates.
Hydrocarbon saturation and fluid contacts tend to be highly uncertain in tight gas reservoirs, this paper demonstrates strategies to gather information on likely fluid content of reservoir zones during the exploration and appraisal stage. Acquisition of representative fluid samples for PVT purposes is also extremely challenging in these type of reservoirs and this paper will outline the success and challenges experienced to date in the North Oman Area, and illustrates examples where good quality samples have been recovered.