Evaluation of the Unconventional Basement Reservoir of Kharir, Yemen: Insight from Fluid Inclusion Stratigraphy (FIS)

Girard, Jean-Pierre; Kluska, Jean-Michel; Champanhet, Jean-Michel

The main specificity of fractured basement petroleum reservoirs is that hydrocarbons essentially occur in fractures. As a consequence it is difficult to 1) make reliable predictions on the location of "sweet-spots", 2) link fracture typology and hydrocarbon content, 3) define water-up-to level or oil-water contact, and 4) evaluate volume of oil in place, unless the fracture network is precisely described. We report here the results of an extensive FIS study conducted on 23 wells in the field of Kharir, Yemen, in order to shed light on the hydrocarbon distribution and the conceptual model of the play.

The FIS technique (Fluid Inclusion Technologies, USA) consists of the bulk analysis (quadrupole mass spectrometer), following sample cleaning and crushing, of the volatile fraction present in fluid inclusions trapped in healed microfissures in minerals. It is applied to cuttings, usually along the entire drilled section of a well. Because fractured basement does not contain any source rock intervals, the measured FIS response can be entirely attributed to intervals rich in hydrocarbon fluid inclusions, representing fractures in which hydrocarbons migrated or accumulated.

Applying this approach to the Kharir field provided a unique way to acquire valuable information for exploration/production strategy, including:

- Precise definition of hydrocarbon-bearing or -migrating fractured intervals along well trajectories, - Fracture ranking according to the intensity of FIS response (weak, moderate, strong), so as to define fracture families with greater potential,
- Existence of a Water Up To (WUT) at 2200 m/msl, with a possible Oil-Water contact at about 2100-2200m/msl,
- Evidence for maximum HC accumulation limited to the ≈500 m/TVD immediately below top basement and along the structural crest (top-to-bottom charging process),
- Record of an evolution in hydrocarbon maturity, from liquid-rich to gas-rich, during charge history,
- Overall consistency in compositional signature of FIS response at field scale, suggesting a common source of hydrocarbons.

In most wells, GWD (Gas While Drilling) data are in good agreement with FIS results, confirming the validity of the approach. The knowledge derived from these results proved useful for the conceptual understanding of the play and the definition of production drilling patterns.

AAPG Search and Discovery Article #90163©2013AAPG 2013 Annual Convention and Exhibition, Pittsburgh, Pennsylvania, May 19-22, 2013