Influence of salt precipitation on reservoir quality Case of Upper Triassic formation - Toual field (SE Algeria)

Toual field is located in the Triassic Province belonging to the Southeastern Saharan platform of Algeria. TAGS reservoir is the French abbreviation of the Upper Triassic Shaley Sandstone Formation. In Toual field, the lower part of TAGS reservoir is deposited in a fluvial environment, while, its upper part is typical of a shallow marine sabkha environment. TAGS is surmounted by a thin clayey Liassic Formation (about 30 m) and a very thick salty Liassic formation (above than 300 m). To predict the effect of halite on TAGS sandstones porosity and permeability we combined some conventional well log measurements (GR, DT, RHOB) in multi-dimensional cross-plots. We also took advantage of recorded unconventional well logs (Pulsed neutron decay time logs and Pressure test logs) and core lab measurements (PHIcore, Kcore and RHOcore). The analysis of the above logs and core data indicates that petrophysical properties of the upper part of TAGS reservoir are considerably affected by halite presence in sandstone as cement filling pores. The presence of similar deposits has been found harmful regarding the reservoir quality. Thus, one of our main targets in that investigation is to find out about the main source of the halite type responsible in the control of reservoir petrophysical characteristics in the TAGS reservoir. Finally we proposed possible sources of halite that exist in the investigated sandstones.