Sedimentology and quantitative well logs petrophysical parameters, lower qishn clastic reservoir, Masila oilfield, Yemen

Abstract EN

Oil in the Masila area was first discovered in late 1990 with commerciality being declared in late 1991.

Oil production at Masila began in July 1993.

About 90% of the oil reserves were found in the Lower Qishn Clastic reservoir of the Lower Cretaceous sequence.

The Lower Cretaceous Qishn Clastic Member in Masila Block14, Republic of Yemen, a primary drilling objective, with estimated reserves of 1.1 billion barrels recoverable oil.

Masila has produced approximately 656 million barrels of oil to date.

Sedimentation took place in an elongate paleo-gulf of the Say’un–al Masila Basin, open to marine carbonates to the east.

The Qishn Clastic Member unconformably overlies mixed carbonates and clastics of the Sa’af Member.

Lower Qishn onlap resulted in deposition of brackish and tidal, estuarine to open bay or gulf deposits.

The middle portion of the lower Qishn Clastic Member shows evidence of arid non-marine sedimentation, including debris flow deposits, red beds and shaleclastic conglomerates, in turn, overlain by interfingering coastal and non-marine deposits.

The porosities determinations of the investigated area from the studied wells indicate that the porosity of the Lower Qishn Clastics are relatively high-and the permeability of this reservoir range from103 to 374 md.

The water saturation shows low values.

On the other hand, the hydrocarbon saturation is in a reverse relation i.e.

the hydrocarbon decreases, where the water saturation increases.

Different Crossplots such as RHOB / NPHI, RHOB / NPHI Matrix, and GR-RHOB GR-NPHI cross plots were determined for lithological identification of the Lower Qishn Clastic in the studied wells, which indicate that it is composed mainly of sandstone with shale and carbonates intercalations.

Such formation evaluation of the obtained petrophysical parameters have frequently proven that the formation hase high hydrocarbon saturation in this area and containing many pay zones.